Derivatives of Rhodobacter capsulatus AD2 unable to grow with nitrate as sole N source were isola... more Derivatives of Rhodobacter capsulatus AD2 unable to grow with nitrate as sole N source were isolated after conjugation with a plasmld containing a cloned 3.4 kb HmdIll fragment from the endogenous plesmad of this strain These derivatives lacked the M r 74 × 106 plasmld found m the wild-type, and faded to revert to growth on mtrate Cultures of the plasrmd-eured strums also lacked dissimilatory mtrate reductase actwlty, suggesting that genes required for both asslrmlatory and dlsslmilatory nitrate reduction are located on the endogenous plasmtd 2 INTRODUCTION The photosynthetic purple non-sulphur bacterium Rhodobacter capsulatus is able to utdlse a wide range of N sources for growth [1] However, the ability to grow with nitrate as sole N source is
Despite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropoge... more Despite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropogenic stresses, the role played by endocrine disruptors (EDs) in the decline of amphibian populations remains unclear. EDs have been extensively studied in adult amphibians for their capacity to disturb reproduction by interfering with the sexual hormone axis.
Abstract Endogenous plasmids are found in most strains of Rhodobacter sphaeroides , Rhodobacter c... more Abstract Endogenous plasmids are found in most strains of Rhodobacter sphaeroides , Rhodobacter capsulatus and Rhodospirillum rubrum , but appear to be less common in other species of purple non-sulphur bacteria. They have also been found in some species of green and purple sulphur bacteria. Until recently, there was little conclusive evidence for the functions of these plasmids, and most were considered to be cryptic. The advent of whole genome sequencing has enabled predictions of possible plasmid functions that can then be tested experimentally. In addition, transcriptomic and proteomic studies in R. sphaeroides 2.4.1 have shown that plasmids play an active role in genome function and may code for essential metabolic processes. This chapter summarises experimental and genomic evidence for plasmid function in the anaerobic anoxygenic phototrophs, with particular emphasis on photosynthetic metabolism, nitrogen oxide reduction, cell wall biosynthesis and heavy metal resistance, and new experimental evidence is presented for the role of the endogenous plasmid in the R. capsulatus strains B10 and SB1003. The evolution of these plasmids will also be considered, and insights from nucleotide sequence comparisons will be combined with those from phylogenetic analysis of plasmid replication modules in the Roseobacter clade of the α- Proteobacteria , which includes aerobic anoxygenic phototrophs.
Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical a... more Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical and chemical effects on microorganisms. The aim of this study was to investigate the effect of ultrasound on the destruction of Mycobacterium strain 6PY1. Ultrasound waves (20 kHz or 612 kHz) were used to treat aqueous suspensions of Mycobacterium at different volumes, initial bacterial concentrations, and power densities. At the same power density and the same exposure time, sonication at high frequency resulted in a lower destruction of Mycobacterium sp. 6PY1 (35.5%) than sonication at low frequency (93%). The percentage of removal was not significantly affected by the volume of the irradiated suspension (150-300 ml) or the initial cell concentration (2.15 Â 10 À3-1.4 Â 10 À2 mg protein L À1). At low frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density, with a constant level reached after a certain power density. At high frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density. The mechanism of cell killing was investigated by examining the effects of OH Å radical scavengers such as sodium carbonate. At high frequency the presence of sodium carbonate suppressed the removal process. However, at low frequency the removal process was not affected, thus indicating that OH Å radicals have a negligible role in this case. The latter result was supported by ten time's H 2 O 2 production at high frequency greater than that at low frequency.
Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Genera... more Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Generally, this attraction is closely associated with herbivory and has been studied mainly under atmospheric conditions. On the other hand, the relationship between aquatic plants and insects has been little studied. To determine whether the roots of aquatic macrophytes release attractive chemical mixtures into the water, we studied the behaviour of mosquito larvae using olfactory experiments with root exudates. After testing the attraction on Culex and Aedes mosquito larvae, we chose to work with Coquillettidia species, which have a complex behaviour in nature and need to be attached to plant roots in order to obtain oxygen. This relationship is non-destructive and can be described as commensal behaviour. Commonly found compounds seemed to be involved in insect attraction since root exudates from different plants were all attractive. Moreover, chemical analysis allowed us to identify a certain number of commonly found, highly water-soluble, low-molecular-weight compounds, several of which (glycerol, uracil, thymine, uridine, thymidine) were able to induce attraction when tested individually but at concentrations substantially higher than those found in nature. However, our principal findings demonstrated that these compounds appeared to act synergistically, since a mixture of these five compounds attracted larvae at natural concentrations (0.7 nM glycerol, ,0.5 nM uracil, 0.6 nM thymine, 2.8 nM uridine, 86 nM thymidine), much lower than those found for each compound tested individually. These results provide strong evidence that a mixture of polyols (glycerol), pyrimidines (uracil, thymine), and nucleosides (uridine, thymidine) functions as an efficient attractive signal in nature for Coquillettidia larvae. We therefore show for the first time, that such commonly found compounds may play an important role in plant-insect relationships in aquatic ecosystems .
Four different mutant strains of Rhodobacter capsulatus (IR1, IR3, IR4 and JP91), a photosyntheti... more Four different mutant strains of Rhodobacter capsulatus (IR1, IR3, IR4 and JP91), a photosynthetic purple non-sulfur bacterium, were tested for their ability to produce hydrogen in a 3L volume photobioreactor coupled to a small PEM fuel cell. The four mutants, together with the wild-type strain, B10, were grown at 30°C under illumination with 30mmolL−1dl-lactate and 5mmolL−1l-glutamate as carbon and nitrogen
The photosynthetic bacterium, Rhodobacter capsulatus, produces hydrogen under nitrogenlimited, an... more The photosynthetic bacterium, Rhodobacter capsulatus, produces hydrogen under nitrogenlimited, anaerobic, photosynthetic culture conditions, using various carbon substrates. In the present study, the relationship between light intensity and hydrogen production has been modelled in order to predict both the rate of hydrogen production and the amount of hydrogen produced at a given time during batch cultures of R. capsulatus. The experimental data were obtained by investigating the effect of different light intensities (6000-50,000 lux) on hydrogen-producing cultures of R. capsulatus grown in a batch photobioreactor, using lactate as carbon and hydrogen source. The rate of hydrogen production increased with increasing light intensity in a manner that was described by a static Baly model, modified to include the square of the light intensity. In agreement with previous studies, the kinetics of substrate utilization and growth of R. capsulatus was represented by the classical Monod or Michaelis-Menten model. When combined with a dynamic Leudekong-Piret model, the amount of hydrogen produced as a function of time was effectively predicted. These results will be useful for the automatization and control of bioprocesses for the photoproduction of hydrogen.
This paper addresses the problem of estimating the states of an anaerobic photosynthetic process ... more This paper addresses the problem of estimating the states of an anaerobic photosynthetic process used for biohydrogen production by the photosynthetic bacterium Rhodobacter capsulatus. The process is described by a non-linear, time-discrete model and the state estimation is solved using an observer based on the Moving-Horizon State Estimation Method (MHSE). This approach is based on the minimization of a criterion (a non-linear function), in this case, the difference between the estimated output and the measured output of the system over a considered time horizon, where the solution is computed by using a numerical interval method. The observer was successfully applied to hydrogen production by R. capsulatus strain B10 in a batch process.
A crucial component for developing insect management strategies is the understanding of the ecolo... more A crucial component for developing insect management strategies is the understanding of the ecological parameters involved in habitat selection by proliferating species. The key ecological drivers underlying habitat selection in the mosquito Coquillettidia sp. have been investigated in natura. Vegetation analysis suggested that the most suitable habitats were ponds with a high vegetation cover maintaining a high degree of humidity in the air. The optimal biotope for Coquillettidia was associated with the presence of larval host plants such as Typha sp., Phragmites sp., and Juncus sp. Water quality was also found to be a key factor in larval habitat distribution. The presence of larvae was significantly correlated with physico-chemical factors and the optimal water characteristics were neutral pH, low salt concentration, and a relatively low level of suspended particulate matter. A significant correlation was observed between chemical cues and the Coquillettidia distribution pattern. For instance, 2,6-di-tert-butyl-p-cresol was positively correlated to larval habitat, whereas high lauric acid and heptadecanoic acid concentrations may be limiting factors. This study underlines the fact that mosquito habitat selection is driven by a complex process based on discriminating levels of several ecological factors. Multivariate analysis helps understand such processes, which is this case will assist in managing expanding populations of a species that threatens human health.
Nif-mutants of Rhodobacter capsulatus carrying mutations either in the nifR4 regulatory gene or i... more Nif-mutants of Rhodobacter capsulatus carrying mutations either in the nifR4 regulatory gene or in the nifH structural gene both outgrew the wild-type strain B10 in mixed chemostat cultures under conditions favouring nitrogenase-mediated H e production by the wild-type (ammonia as limiting nutrient, inert argon atmosphere, light as energy source), whereas under aerobic conditions in the dark, or in batch culture, the growth of Nif-mutants was not favoured. Nitrogenasemediated H e production therefore appears to be detrimental to the growth of R. capsulatus in nitrogen-limited continuous culture, as may also be the case for other nitrogen fixers. 2. INTRODUCTION Nitrogen fixation is known to be a highly energy requiring process, although the exact energy
Two mutants of Rhodobacter Capsulatus (JP91 and IR3), a photosynthetic purple non-sulfur bacteriu... more Two mutants of Rhodobacter Capsulatus (JP91 and IR3), a photosynthetic purple non-sulfur bacterium, were grown in a batch photobioreactor under illumination with 30 mmol l −1 dl-lactate and 5 mmol l −1 l-glutamate as carbon and nitrogen source, respectively. Bacterial growth was measured by monitoring the increase in absorbance at 660 nm. The photosynthetic growth processes under different cultivated temperatures are well fitted by a specific logistic model to analyze the kinetics of photosynthetic growth of two strains, thus the apparent growth rates (k) of these photosynthetic bacteria, the variations of cell dry weight (CDW) as well as their relationship with temperature are obtained. In present work, k is (0.1465 ± 0.0146), (0.2266 ± 0.0207) and (0.3963 ± 0.0257) h −1 for JP91 and (0.1117 ± 0.0122), (0.1218 ± 0.0133) and (0.2223 ± 0.0152) h −1 for IR3 at 26, 30 and 34 • C, respectively. And the difference between CDW max and CDW 0 is (0.8997 ± 0.0097), (0.8585 ± 0.0093) and (0.9241 ± 0.0099) g l −1 for JP91 and (0.8167 ± 0.0089), (0.7878 ± 0.0086) and (0.8358 ± 0.0091) g l −1 for IR3 at 26, 30 and 34 • C, respectively. Also real-time monitoring of hydrogen production rates is acquired by recording the flow rates of photohydrogen for these two strains under different temperatures. The effects of temperature on the bacteria growth, hydrogen production capability and substrate conversion efficiency are discussed based on these results. The most preferment temperature, 30 • C, showed good substrate conversion efficiency of 52.7 and 68.2% for JP91 and IR3, respectively.
Metal pollution of solid matrices, like soils, sediments and sludge, is widespread across the glo... more Metal pollution of solid matrices, like soils, sediments and sludge, is widespread across the globe, and the clean-up of these matrices presents many difficulties. The aim of this study was to develop an efficient leaching technique for metal removal from an industrial carbon sludge contaminated with Zn (8600 mg kg(-1)) and Pb (389 mg kg(-1)). To this end, the possibility of coupling processes, such as extraction with mineral acids, EDTA addition, ultrasound and bioleaching, was investigated. Lead, but not zinc, was totally removed by EDTA treatment (1200 mg L(-1), pH 6.0). Ultrasound treatment was ineffective in metal leaching at all tested pH values, either with or without EDTA addition, probably because of the reduction in size of the carbon particles and the concomitant increase in surface area available for metal binding. A ferrous-iron-oxidizing, endogenous microflora lixiviated 90% of Zn at pH 2.5 in seven days, whereas, after the addition of Acidithiobacillus ferrooxidans, 100% of Zn was removed within four days. These results indicated that the clean-up process for the metal-contaminated sludge should combine an initial chelation step with Na-EDTA (pH 6.0) for complete removal of Pb, followed by a second bioleaching step with A. ferrooxidans for total removal of Zn.
Fipronil is a recently discovered insecticide of the phenylpyrazole series. It has a highly selec... more Fipronil is a recently discovered insecticide of the phenylpyrazole series. It has a highly selective biochemical mode of action, which has led to its use in a large number of important agronomical, household, and veterinary applications. Previous studies have shown that, during exposure to light, fipronil is converted into a desulfurated derivative (desulfinyl-fipronil), which has slightly reduced insecticidal activity. In this study, the photodegradation of fipronil was studied in solution at low light intensities (sunlight or UV lamp). In addition to desulfinyl-fipronil, a large number of minor photoproducts were observed, including diversely substituted phenylpyrazole derivatives and aniline derivatives that had lost the pyrazole ring. Desulfinylfipronil itself was shown to be relatively stable under both UV light and sunlight, with only limited changes occurring in the substitution of the aromatic ring. Since this compound accumulated to levels corresponding to only 30-55% of the amount of fipronil degraded, it was concluded that one or more alternative pathways of photodegradation must be operating. On the basis of the structurally identified photoproducts, it is proposed that fipronil photodegradation occurs via at least two distinct pathways, one of which involves desulfuration at the 4-position of the pyrazole ring giving the desulfinyl derivative and the other of which involves a different modification of the 4-substituent, leading to cleavage of the pyrazole ring and the formation of aniline derivatives. The latter compounds do not accumulate to high levels and may, therefore, be degraded further. The ecological significance of these results is discussed, particularly with regard to the insecticidal activity of the photoproducts.
Seed-coating with the insecticide fipronil has been intensively used in sunflower cultivation to ... more Seed-coating with the insecticide fipronil has been intensively used in sunflower cultivation to control soil pests such as wireworms. A research project was undertaken to determine the soil distribution of fipronil and of its main phenylpyrazole metabolites. Under agronomic conditions, the quantity of fipronil in the seed-coat (437 microg/seed) decreased continuously during the cultivation period (3.9 microg day(-1) during the first two months; 0.3 microg day(-1) during the next four months). At the end of the cultivation period, 42% of all phenylpyrazole compounds remained in the seed-coat. Fipro nil was poorly mobile in soil, and at the end of the cultivation period it was mostly concentrated in the soil layer close to the seed (3240 microg kg(-1) soil). Starting from the seed-coating, a fipronil concentration gradient was measured in the soil, up to a distance of 11 cm from the seed. Degradation in the soil occurred at a moderate rate, probably due to the fact that water solubilization of the solid active ingredient present in the seed coating was rate limiting. Indeed, after 6 months of cultivation, only 51% of the fipronil seed-coating was found in the soil, about 7% having been absorbed by the sunflower plant, and 42% remaining in the seed coat. The predominant metabolites produced in the soil were sulfone-fipronil, sulfide-fipronil and amide-fipronil, which were produced at average rates of 5 microg kg(-1) soil day(-1), 3 microg kg(-1) soil day(-1), and 0.4 microg kg(-1) soil day(-1), respectively. In contrast, the photoproduct, desulfinyl-fipronil, was barely detected. All phenylpyrazole compounds were poorly mobile, except for the amide derivative, which is devoid of insecticidal activity in marked contrast to the other metabolites. Furthermore, detectable soil contamination was limited to a zone of about 11 cm around the seed.
A phenanthrene-degrading Mycobacterium sp. strain 6PY1 was grown in an aqueous/organic biphasic c... more A phenanthrene-degrading Mycobacterium sp. strain 6PY1 was grown in an aqueous/organic biphasic culture system with phenanthrene as sole carbon source. Its capacity of degradation was studied during sequential inoculum enrichments, reaching complete phenanthrene degradation at a maximim rate of 7 mg l(-1) h(-1). Water-oil emulsions and biofilm formation were observed in biphasic cultures after four successive enrichments. The factors influencing interfacial area in the emulsions were: the initial phenanthrene concentration, the initial inoculum size, and the silicone oil volume fraction. The results showed that the interfacial area was mainly dependent on the silicone oil/mineral salts medium ratio and the inoculum size.
Oxygen and substrate supply have always been considered physical constraints for the performance ... more Oxygen and substrate supply have always been considered physical constraints for the performance and operation of two-phase partitioning bioreactors (TPPB), widely used for the degradation of hydrophobic substrates. In this regard, the potential advantages of static mixers in upgrading the oxygen transfer and liquid-liquid dispersions in TPPB have been highlighted. In the present paper, the concomitant influence of static mixers on the gas-liquid mass transfer coefficient k L a and on substrate bioavailability was examined in TPPB. The static method based on conventional forms was developed to estimate the oxygen volumetric mass transfer coefficient. Over a broad range of liquid and air flow rates, the presence of static mixers was found to significantly enhance k L a relative to a mixer-free mode of operation. For identical conditions, static mixers improved the k L a threefold. In the presence of external aeration supply, the boost in the k L a was associated with an increase of 16% in the phenanthrene biodegradation rate due to bubble break up accomplished by the static mixers. On the other hand, static mixers were efficient in enhancing substrate bioavailability by improving the liquid-liquid interfacial area. This effect was reflected by a threefold increase in the degradation rate in the bioreactors with no external supply of air when equipped with static mixers.
In the present paper, the degradation of phenanthrene, a model polycyclic aromatic hydrocarbon co... more In the present paper, the degradation of phenanthrene, a model polycyclic aromatic hydrocarbon compound, by the Mycobacterium strain 6PY1 was optimized in a biphasic culture medium. The optimization and modeling were performed using the design of experiments methodology. The temperature, the silicone oil/mineral salts medium volume ratio, and the initial cell concentration, were used as the central composite design parameters. In all experiments, the phenanthrene was degraded to undetectable levels. Response surface methodology was successfully employed to derive an empirical model describing the rate and time of degradation and to deduce the optimal degradation conditions. As a result of the optimization processes, the optimal responses for the degradation rate, the volumetric degradation rate, and the 90% degradation time were estimated to be 0.172 mg h −1 , 22 mg l −1 h −1 , and 18 h, respectively.
Derivatives of Rhodobacter capsulatus AD2 unable to grow with nitrate as sole N source were isola... more Derivatives of Rhodobacter capsulatus AD2 unable to grow with nitrate as sole N source were isolated after conjugation with a plasmld containing a cloned 3.4 kb HmdIll fragment from the endogenous plesmad of this strain These derivatives lacked the M r 74 × 106 plasmld found m the wild-type, and faded to revert to growth on mtrate Cultures of the plasrmd-eured strums also lacked dissimilatory mtrate reductase actwlty, suggesting that genes required for both asslrmlatory and dlsslmilatory nitrate reduction are located on the endogenous plasmtd 2 INTRODUCTION The photosynthetic purple non-sulphur bacterium Rhodobacter capsulatus is able to utdlse a wide range of N sources for growth [1] However, the ability to grow with nitrate as sole N source is
Despite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropoge... more Despite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropogenic stresses, the role played by endocrine disruptors (EDs) in the decline of amphibian populations remains unclear. EDs have been extensively studied in adult amphibians for their capacity to disturb reproduction by interfering with the sexual hormone axis.
Abstract Endogenous plasmids are found in most strains of Rhodobacter sphaeroides , Rhodobacter c... more Abstract Endogenous plasmids are found in most strains of Rhodobacter sphaeroides , Rhodobacter capsulatus and Rhodospirillum rubrum , but appear to be less common in other species of purple non-sulphur bacteria. They have also been found in some species of green and purple sulphur bacteria. Until recently, there was little conclusive evidence for the functions of these plasmids, and most were considered to be cryptic. The advent of whole genome sequencing has enabled predictions of possible plasmid functions that can then be tested experimentally. In addition, transcriptomic and proteomic studies in R. sphaeroides 2.4.1 have shown that plasmids play an active role in genome function and may code for essential metabolic processes. This chapter summarises experimental and genomic evidence for plasmid function in the anaerobic anoxygenic phototrophs, with particular emphasis on photosynthetic metabolism, nitrogen oxide reduction, cell wall biosynthesis and heavy metal resistance, and new experimental evidence is presented for the role of the endogenous plasmid in the R. capsulatus strains B10 and SB1003. The evolution of these plasmids will also be considered, and insights from nucleotide sequence comparisons will be combined with those from phylogenetic analysis of plasmid replication modules in the Roseobacter clade of the α- Proteobacteria , which includes aerobic anoxygenic phototrophs.
Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical a... more Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical and chemical effects on microorganisms. The aim of this study was to investigate the effect of ultrasound on the destruction of Mycobacterium strain 6PY1. Ultrasound waves (20 kHz or 612 kHz) were used to treat aqueous suspensions of Mycobacterium at different volumes, initial bacterial concentrations, and power densities. At the same power density and the same exposure time, sonication at high frequency resulted in a lower destruction of Mycobacterium sp. 6PY1 (35.5%) than sonication at low frequency (93%). The percentage of removal was not significantly affected by the volume of the irradiated suspension (150-300 ml) or the initial cell concentration (2.15 Â 10 À3-1.4 Â 10 À2 mg protein L À1). At low frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density, with a constant level reached after a certain power density. At high frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density. The mechanism of cell killing was investigated by examining the effects of OH Å radical scavengers such as sodium carbonate. At high frequency the presence of sodium carbonate suppressed the removal process. However, at low frequency the removal process was not affected, thus indicating that OH Å radicals have a negligible role in this case. The latter result was supported by ten time's H 2 O 2 production at high frequency greater than that at low frequency.
Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Genera... more Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Generally, this attraction is closely associated with herbivory and has been studied mainly under atmospheric conditions. On the other hand, the relationship between aquatic plants and insects has been little studied. To determine whether the roots of aquatic macrophytes release attractive chemical mixtures into the water, we studied the behaviour of mosquito larvae using olfactory experiments with root exudates. After testing the attraction on Culex and Aedes mosquito larvae, we chose to work with Coquillettidia species, which have a complex behaviour in nature and need to be attached to plant roots in order to obtain oxygen. This relationship is non-destructive and can be described as commensal behaviour. Commonly found compounds seemed to be involved in insect attraction since root exudates from different plants were all attractive. Moreover, chemical analysis allowed us to identify a certain number of commonly found, highly water-soluble, low-molecular-weight compounds, several of which (glycerol, uracil, thymine, uridine, thymidine) were able to induce attraction when tested individually but at concentrations substantially higher than those found in nature. However, our principal findings demonstrated that these compounds appeared to act synergistically, since a mixture of these five compounds attracted larvae at natural concentrations (0.7 nM glycerol, ,0.5 nM uracil, 0.6 nM thymine, 2.8 nM uridine, 86 nM thymidine), much lower than those found for each compound tested individually. These results provide strong evidence that a mixture of polyols (glycerol), pyrimidines (uracil, thymine), and nucleosides (uridine, thymidine) functions as an efficient attractive signal in nature for Coquillettidia larvae. We therefore show for the first time, that such commonly found compounds may play an important role in plant-insect relationships in aquatic ecosystems .
Four different mutant strains of Rhodobacter capsulatus (IR1, IR3, IR4 and JP91), a photosyntheti... more Four different mutant strains of Rhodobacter capsulatus (IR1, IR3, IR4 and JP91), a photosynthetic purple non-sulfur bacterium, were tested for their ability to produce hydrogen in a 3L volume photobioreactor coupled to a small PEM fuel cell. The four mutants, together with the wild-type strain, B10, were grown at 30°C under illumination with 30mmolL−1dl-lactate and 5mmolL−1l-glutamate as carbon and nitrogen
The photosynthetic bacterium, Rhodobacter capsulatus, produces hydrogen under nitrogenlimited, an... more The photosynthetic bacterium, Rhodobacter capsulatus, produces hydrogen under nitrogenlimited, anaerobic, photosynthetic culture conditions, using various carbon substrates. In the present study, the relationship between light intensity and hydrogen production has been modelled in order to predict both the rate of hydrogen production and the amount of hydrogen produced at a given time during batch cultures of R. capsulatus. The experimental data were obtained by investigating the effect of different light intensities (6000-50,000 lux) on hydrogen-producing cultures of R. capsulatus grown in a batch photobioreactor, using lactate as carbon and hydrogen source. The rate of hydrogen production increased with increasing light intensity in a manner that was described by a static Baly model, modified to include the square of the light intensity. In agreement with previous studies, the kinetics of substrate utilization and growth of R. capsulatus was represented by the classical Monod or Michaelis-Menten model. When combined with a dynamic Leudekong-Piret model, the amount of hydrogen produced as a function of time was effectively predicted. These results will be useful for the automatization and control of bioprocesses for the photoproduction of hydrogen.
This paper addresses the problem of estimating the states of an anaerobic photosynthetic process ... more This paper addresses the problem of estimating the states of an anaerobic photosynthetic process used for biohydrogen production by the photosynthetic bacterium Rhodobacter capsulatus. The process is described by a non-linear, time-discrete model and the state estimation is solved using an observer based on the Moving-Horizon State Estimation Method (MHSE). This approach is based on the minimization of a criterion (a non-linear function), in this case, the difference between the estimated output and the measured output of the system over a considered time horizon, where the solution is computed by using a numerical interval method. The observer was successfully applied to hydrogen production by R. capsulatus strain B10 in a batch process.
A crucial component for developing insect management strategies is the understanding of the ecolo... more A crucial component for developing insect management strategies is the understanding of the ecological parameters involved in habitat selection by proliferating species. The key ecological drivers underlying habitat selection in the mosquito Coquillettidia sp. have been investigated in natura. Vegetation analysis suggested that the most suitable habitats were ponds with a high vegetation cover maintaining a high degree of humidity in the air. The optimal biotope for Coquillettidia was associated with the presence of larval host plants such as Typha sp., Phragmites sp., and Juncus sp. Water quality was also found to be a key factor in larval habitat distribution. The presence of larvae was significantly correlated with physico-chemical factors and the optimal water characteristics were neutral pH, low salt concentration, and a relatively low level of suspended particulate matter. A significant correlation was observed between chemical cues and the Coquillettidia distribution pattern. For instance, 2,6-di-tert-butyl-p-cresol was positively correlated to larval habitat, whereas high lauric acid and heptadecanoic acid concentrations may be limiting factors. This study underlines the fact that mosquito habitat selection is driven by a complex process based on discriminating levels of several ecological factors. Multivariate analysis helps understand such processes, which is this case will assist in managing expanding populations of a species that threatens human health.
Nif-mutants of Rhodobacter capsulatus carrying mutations either in the nifR4 regulatory gene or i... more Nif-mutants of Rhodobacter capsulatus carrying mutations either in the nifR4 regulatory gene or in the nifH structural gene both outgrew the wild-type strain B10 in mixed chemostat cultures under conditions favouring nitrogenase-mediated H e production by the wild-type (ammonia as limiting nutrient, inert argon atmosphere, light as energy source), whereas under aerobic conditions in the dark, or in batch culture, the growth of Nif-mutants was not favoured. Nitrogenasemediated H e production therefore appears to be detrimental to the growth of R. capsulatus in nitrogen-limited continuous culture, as may also be the case for other nitrogen fixers. 2. INTRODUCTION Nitrogen fixation is known to be a highly energy requiring process, although the exact energy
Two mutants of Rhodobacter Capsulatus (JP91 and IR3), a photosynthetic purple non-sulfur bacteriu... more Two mutants of Rhodobacter Capsulatus (JP91 and IR3), a photosynthetic purple non-sulfur bacterium, were grown in a batch photobioreactor under illumination with 30 mmol l −1 dl-lactate and 5 mmol l −1 l-glutamate as carbon and nitrogen source, respectively. Bacterial growth was measured by monitoring the increase in absorbance at 660 nm. The photosynthetic growth processes under different cultivated temperatures are well fitted by a specific logistic model to analyze the kinetics of photosynthetic growth of two strains, thus the apparent growth rates (k) of these photosynthetic bacteria, the variations of cell dry weight (CDW) as well as their relationship with temperature are obtained. In present work, k is (0.1465 ± 0.0146), (0.2266 ± 0.0207) and (0.3963 ± 0.0257) h −1 for JP91 and (0.1117 ± 0.0122), (0.1218 ± 0.0133) and (0.2223 ± 0.0152) h −1 for IR3 at 26, 30 and 34 • C, respectively. And the difference between CDW max and CDW 0 is (0.8997 ± 0.0097), (0.8585 ± 0.0093) and (0.9241 ± 0.0099) g l −1 for JP91 and (0.8167 ± 0.0089), (0.7878 ± 0.0086) and (0.8358 ± 0.0091) g l −1 for IR3 at 26, 30 and 34 • C, respectively. Also real-time monitoring of hydrogen production rates is acquired by recording the flow rates of photohydrogen for these two strains under different temperatures. The effects of temperature on the bacteria growth, hydrogen production capability and substrate conversion efficiency are discussed based on these results. The most preferment temperature, 30 • C, showed good substrate conversion efficiency of 52.7 and 68.2% for JP91 and IR3, respectively.
Metal pollution of solid matrices, like soils, sediments and sludge, is widespread across the glo... more Metal pollution of solid matrices, like soils, sediments and sludge, is widespread across the globe, and the clean-up of these matrices presents many difficulties. The aim of this study was to develop an efficient leaching technique for metal removal from an industrial carbon sludge contaminated with Zn (8600 mg kg(-1)) and Pb (389 mg kg(-1)). To this end, the possibility of coupling processes, such as extraction with mineral acids, EDTA addition, ultrasound and bioleaching, was investigated. Lead, but not zinc, was totally removed by EDTA treatment (1200 mg L(-1), pH 6.0). Ultrasound treatment was ineffective in metal leaching at all tested pH values, either with or without EDTA addition, probably because of the reduction in size of the carbon particles and the concomitant increase in surface area available for metal binding. A ferrous-iron-oxidizing, endogenous microflora lixiviated 90% of Zn at pH 2.5 in seven days, whereas, after the addition of Acidithiobacillus ferrooxidans, 100% of Zn was removed within four days. These results indicated that the clean-up process for the metal-contaminated sludge should combine an initial chelation step with Na-EDTA (pH 6.0) for complete removal of Pb, followed by a second bioleaching step with A. ferrooxidans for total removal of Zn.
Fipronil is a recently discovered insecticide of the phenylpyrazole series. It has a highly selec... more Fipronil is a recently discovered insecticide of the phenylpyrazole series. It has a highly selective biochemical mode of action, which has led to its use in a large number of important agronomical, household, and veterinary applications. Previous studies have shown that, during exposure to light, fipronil is converted into a desulfurated derivative (desulfinyl-fipronil), which has slightly reduced insecticidal activity. In this study, the photodegradation of fipronil was studied in solution at low light intensities (sunlight or UV lamp). In addition to desulfinyl-fipronil, a large number of minor photoproducts were observed, including diversely substituted phenylpyrazole derivatives and aniline derivatives that had lost the pyrazole ring. Desulfinylfipronil itself was shown to be relatively stable under both UV light and sunlight, with only limited changes occurring in the substitution of the aromatic ring. Since this compound accumulated to levels corresponding to only 30-55% of the amount of fipronil degraded, it was concluded that one or more alternative pathways of photodegradation must be operating. On the basis of the structurally identified photoproducts, it is proposed that fipronil photodegradation occurs via at least two distinct pathways, one of which involves desulfuration at the 4-position of the pyrazole ring giving the desulfinyl derivative and the other of which involves a different modification of the 4-substituent, leading to cleavage of the pyrazole ring and the formation of aniline derivatives. The latter compounds do not accumulate to high levels and may, therefore, be degraded further. The ecological significance of these results is discussed, particularly with regard to the insecticidal activity of the photoproducts.
Seed-coating with the insecticide fipronil has been intensively used in sunflower cultivation to ... more Seed-coating with the insecticide fipronil has been intensively used in sunflower cultivation to control soil pests such as wireworms. A research project was undertaken to determine the soil distribution of fipronil and of its main phenylpyrazole metabolites. Under agronomic conditions, the quantity of fipronil in the seed-coat (437 microg/seed) decreased continuously during the cultivation period (3.9 microg day(-1) during the first two months; 0.3 microg day(-1) during the next four months). At the end of the cultivation period, 42% of all phenylpyrazole compounds remained in the seed-coat. Fipro nil was poorly mobile in soil, and at the end of the cultivation period it was mostly concentrated in the soil layer close to the seed (3240 microg kg(-1) soil). Starting from the seed-coating, a fipronil concentration gradient was measured in the soil, up to a distance of 11 cm from the seed. Degradation in the soil occurred at a moderate rate, probably due to the fact that water solubilization of the solid active ingredient present in the seed coating was rate limiting. Indeed, after 6 months of cultivation, only 51% of the fipronil seed-coating was found in the soil, about 7% having been absorbed by the sunflower plant, and 42% remaining in the seed coat. The predominant metabolites produced in the soil were sulfone-fipronil, sulfide-fipronil and amide-fipronil, which were produced at average rates of 5 microg kg(-1) soil day(-1), 3 microg kg(-1) soil day(-1), and 0.4 microg kg(-1) soil day(-1), respectively. In contrast, the photoproduct, desulfinyl-fipronil, was barely detected. All phenylpyrazole compounds were poorly mobile, except for the amide derivative, which is devoid of insecticidal activity in marked contrast to the other metabolites. Furthermore, detectable soil contamination was limited to a zone of about 11 cm around the seed.
A phenanthrene-degrading Mycobacterium sp. strain 6PY1 was grown in an aqueous/organic biphasic c... more A phenanthrene-degrading Mycobacterium sp. strain 6PY1 was grown in an aqueous/organic biphasic culture system with phenanthrene as sole carbon source. Its capacity of degradation was studied during sequential inoculum enrichments, reaching complete phenanthrene degradation at a maximim rate of 7 mg l(-1) h(-1). Water-oil emulsions and biofilm formation were observed in biphasic cultures after four successive enrichments. The factors influencing interfacial area in the emulsions were: the initial phenanthrene concentration, the initial inoculum size, and the silicone oil volume fraction. The results showed that the interfacial area was mainly dependent on the silicone oil/mineral salts medium ratio and the inoculum size.
Oxygen and substrate supply have always been considered physical constraints for the performance ... more Oxygen and substrate supply have always been considered physical constraints for the performance and operation of two-phase partitioning bioreactors (TPPB), widely used for the degradation of hydrophobic substrates. In this regard, the potential advantages of static mixers in upgrading the oxygen transfer and liquid-liquid dispersions in TPPB have been highlighted. In the present paper, the concomitant influence of static mixers on the gas-liquid mass transfer coefficient k L a and on substrate bioavailability was examined in TPPB. The static method based on conventional forms was developed to estimate the oxygen volumetric mass transfer coefficient. Over a broad range of liquid and air flow rates, the presence of static mixers was found to significantly enhance k L a relative to a mixer-free mode of operation. For identical conditions, static mixers improved the k L a threefold. In the presence of external aeration supply, the boost in the k L a was associated with an increase of 16% in the phenanthrene biodegradation rate due to bubble break up accomplished by the static mixers. On the other hand, static mixers were efficient in enhancing substrate bioavailability by improving the liquid-liquid interfacial area. This effect was reflected by a threefold increase in the degradation rate in the bioreactors with no external supply of air when equipped with static mixers.
In the present paper, the degradation of phenanthrene, a model polycyclic aromatic hydrocarbon co... more In the present paper, the degradation of phenanthrene, a model polycyclic aromatic hydrocarbon compound, by the Mycobacterium strain 6PY1 was optimized in a biphasic culture medium. The optimization and modeling were performed using the design of experiments methodology. The temperature, the silicone oil/mineral salts medium volume ratio, and the initial cell concentration, were used as the central composite design parameters. In all experiments, the phenanthrene was degraded to undetectable levels. Response surface methodology was successfully employed to derive an empirical model describing the rate and time of degradation and to deduce the optimal degradation conditions. As a result of the optimization processes, the optimal responses for the degradation rate, the volumetric degradation rate, and the 90% degradation time were estimated to be 0.172 mg h −1 , 22 mg l −1 h −1 , and 18 h, respectively.
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Papers by John Willison