Papers by André Rodrigues
Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology, 2009
We investigate the diversity of yeasts isolated in gardens of the leafcutter ant Atta texana. Rep... more We investigate the diversity of yeasts isolated in gardens of the leafcutter ant Atta texana. Repeated sampling of gardens from four nests over a 1-year time period showed that gardens contain a diverse assemblage of yeasts. The yeast community in gardens consisted mostly of yeasts associated with plants or soil, but community composition changed between sampling periods. In order to understand the potential disease-suppressing roles of the garden yeasts, we screened isolates for antagonistic effects against known microfungal garden contaminants. In vitro assays revealed that yeasts inhibited the mycelial growth of two strains of Escovopsis (a specialized attine garden parasite), Syncephalastrum racemosum (a fungus often growing in gardens of leafcutter lab nests), and the insect pathogen Beauveria bassiana. These garden yeasts add to the growing list of disease-suppressing microbes in attine nests that may contribute synergistically, together with actinomycetes and Burkholderia bacteria, to protect the gardens and the ants against diseases. Additionally, we suggest that garden immunity against problem fungi may therefore derive not only from the presence of disease-suppressing Pseudonocardia actinomycetes, but from an enrichment of multiple disease-suppressing microorganisms in the garden matrix.
Evolution, 2008
We reassess the coevolution between actinomycete bacteria and fungus-gardening (attine) ants. Act... more We reassess the coevolution between actinomycete bacteria and fungus-gardening (attine) ants. Actinomycete bacteria are of special interest because they are metabolic mutualists of diverse organisms (e.g., in nitrogen-fixation or antibiotic production) and because Pseudonocardia actinomycetes are thought to serve disease-suppressing functions in attine gardens. Phylogenetic information from culture-dependent and culture-independent microbial surveys reveals (1) close affinities between free-living and ant-associated Pseudonocardia, and (2) essentially no topological correspondence between ant and Pseudonocardia phylogenies, indicating frequent bacterial acquisition from environmental sources. Identity of ant-associated Pseudonocardia and isolates from soil and plants implicates these environments as sources from which attine ants acquire Pseudonocardia. Close relatives of Atta leafcutter ants have abundant Pseudonocardia, but Pseudonocardia in Atta is rare and appears at the level of environmental contamination. In contrast, actinomycete bacteria in the genera Mycobacterium and Microbacterium can be readily isolated from gardens and starter-cultures of Atta. The accumulated phylogenetic evidence is inconsistent with prevailing views of specific coevolution between Pseudonocardia, attine ants, and garden diseases. Because of frequent acquisition, current models of Pseudonocardia-disease coevolution now need to be revised. The effectiveness of Pseudonocardia antibiotics may not derive from advantages in the coevolutionary arms race with specialized garden diseases, as currently believed, but from frequent recruitment of effective microbes from environmental sources. Indeed, the exposed integumental structures that support actinomycete growth on attine ants argue for a morphological design facilitating bacterial recruitment. We review the accumulated evidence that attine ants have undergone modifications in association with actinomycete bacteria, but we find insufficient support for the reverse, modifications of the bacteria resulting from the interaction with attine ants. The defining feature of coevolution—reciprocal modification—therefore remains to be established for the attine ant-actinomycete mutualism.
Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology, 2008
Insect-associated microbes exhibit a wide range of interactions with their hosts. One example of ... more Insect-associated microbes exhibit a wide range of interactions with their hosts. One example of such interactions is the insect-driven dispersal of microorganisms, which plays an essential role in the ecology of several microbes. To study dispersal of microorganisms by leaf-cutting ants (Formicidae: Attini), we applied culture-dependent methods to identify the filamentous fungi and yeasts found in two different body parts of leaf-cutting ant gynes: the exoskeleton and the infrabuccal pocket. The gynes use the latter structure to store a pellet of the ants' symbiotic fungus during nest founding. Many filamentous fungi (n = 142) and yeasts (n = 19) were isolated from the gynes' exoskeleton. In contrast, only seven filamentous fungi and three yeasts isolates were recovered from the infrabuccal pellets, suggesting an efficient mechanism utilized by the gynes to prevent contamination of the symbiotic fungus inoculum. The genus Cladosporium prevailed (78%) among filamentous fungi whereas Aureobasidium, Candida and Cryptococcus prevailed among yeasts associated with gynes. Interestingly, Escovopsis, a specialized fungal pathogen of the leaf-cutting antfungus symbiosis, was not isolated from the body parts or from infrabuccal pellets of any gynes sampled. Our results suggest that gynes of the leafcutter ants Atta laevigata and A. capiguara do not vertically transmit any particular species of yeasts or filamentous fungi during the foundation of a new nest. Instead, fungi found in association with gynes have a cosmopolitan distribution, suggesting they are probably acquired from the environment and passively dispersed during nest foundation. The possible role of these fungi for the attine ant-microbial symbiosis is discussed.
Folia Microbiologica, 2005
A survey of the filamentous fungi other than the symbiotic one found in association withAtta sexd... more A survey of the filamentous fungi other than the symbiotic one found in association withAtta sexdens rubropilosa colonies was carried out. Different fungal species (27 taxa) were isolated a few days after treating the workers with toxic baits (sulfluramid; Mirex-S®), from 40 laboratory and 20 field nests.Syncephalastrum racemosum (54 %) andEscovopsis weberi (21 %),Trichoderma harzianum (38 %) andFusarium oxysporum (23 %) were the prevalent species in laboratory and field nests, respectively.Acremonium kiliense, Acremonium strictum, E. weberi, F. oxysporum, Fusarium solani, Moniliella suaveolens andT. harzianum were found in both nests’ groups. We revealed that many filamentous fungi can co-exist in a dormant state inside the nests of these insects and some of them appear to be tightly associated with this environment.
Microbial Ecology, 2008
Leafcutter ants (Formicidae: tribe Attini) are well-known insects that cultivate basidiomycete fu... more Leafcutter ants (Formicidae: tribe Attini) are well-known insects that cultivate basidiomycete fungi (Agaricales: Lepiotaceae) as their principal food. Fungus gardens are monocultures of a single cultivar strain, but they also harbor a diverse assemblage of additional microbes with largely unknown roles in the symbiosis. Cultivar-attacking microfungi in the genus Escovopsis are specialized parasites found only in association with attine gardens. Evolutionary theory predicts that the low genetic diversity in monocultures should render ant gardens susceptible to a wide range of diseases, and additional parasites with roles similar to that of Escovopsis are expected to exist. We profiled the diversity of cultivable microfungi found in 37 nests from ten Acromyrmex species from Southern Brazil and compared this diversity to published surveys. Our study revealed a total of 85 microfungal strains. Fusarium oxysporum and Escovopsis were the predominant species in the surveyed gardens, infecting 40.5% and 27% of the nests, respectively. No specific relationship existed regarding microfungal species and ant-host species, ant substrate preference (dicot versus grass) or nesting habit. Molecular data indicated high genetic diversity among Escovopsis isolates. In contrast to the garden parasite, F. oxysporum strains are not specific parasites of the cultivated fungus because strains isolated from attine gardens have similar counterparts found in the environment. Overall, the survey indicates that saprophytic microfungi are prevalent in South American leafcutter ants. We discuss the antagonistic potential of these microorganisms as “weeds” in the ant–fungus symbiosis.
Network Simulators are important tools in network research. As the selected topology often influe... more Network Simulators are important tools in network research. As the selected topology often influences the outcome of the simulation, realistic topologies are required to produce realistic simulation results. The topology generator presented in this document, GenSeN, was created based on the authors' knowledge from several experiences. GenSeN is a tool capable of generating realistic topologies of wireless sensor networks and, additionally, auto-configuring important characteristics of sensor nodes, such as energy parameters. The tool was validated by comparison with real deployment strategies and experiences.
Journal of Networks, 2008
Multicast potentially optimises bandwidth consumption and node resources, when several users simu... more Multicast potentially optimises bandwidth consumption and node resources, when several users simultaneously participate in a communication session. Nevertheless, contrary to the expectations, IP multicast has not experienced widespread deployment, with the exception of IPTV. On the other hand, emerging Wireless Sensor Network (WSN) applications could greatly benefit from multicast and constitute another field where multicast can be an effective and efficient technique. The questions are: do multicast advantages hold in WSN scenarios? Can we use IP Multicast functionality in WSNs? This paper discusses and evaluates the use of multicast in WSNs.
... The mobility concept in WSN is somehow complex, since it presents several external variables ... more ... The mobility concept in WSN is somehow complex, since it presents several external variables that need to be considered. The mobility perception in WSN presents several differences from current ad hoc mobile approaches. ...
Brazilian Journal of Medical and Biological Research, 1998
We investigated the effects of lead exposure during the pre-and postnatal period on the neurobeha... more We investigated the effects of lead exposure during the pre-and postnatal period on the neurobehavioral development of female Wistar rats (70-75 days of age, 120-150 g) using a protocol of lead intoxication that does not affect weight gain. Wistar rats were submitted to lead acetate intoxication by giving their dams 1.0 mM lead acetate. Control dams received deionized water. Growth and neuromotor development were assessed by monitoring daily the following parameters in 20 litters: body weight, ear unfolding, incisor eruption, eye opening, righting, palmar grasp, negative geotaxis, cliff avoidance and startle reflex. Spontaneous alternation was assessed on postnatal day 17 using a T maze. The animals' ability to equilibrate on a beaker rim was measured on postnatal day 19. Lead intoxication was confirmed by measuring renal, hepatic and cerebral lead concentration in dams and litters. Lead treatment hastened the day of appearance of the following parameters: eye opening (control: 13.5 ± 0.6, N = 88; lead: 12.9 ± 0.6, N = 72; P<0.05), startle reflex (control: 13.0 ± 0.8, N = 88; lead: 12.0 ± 0.7, N = 72; P<0.05) and negative geotaxis. On the other hand, spontaneous alternation performance was hindered in lead-exposed animals (control: 37.6 ± 19.7; lead: 57.5 ± 28.3% of alternating animals; P<0.05). These results suggest that lead exposure without concomitant undernutrition alters rat development, affecting specific subsets of motor skills.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
Nanocomposites containing polyethylene (PE) and montmorillonite clay organically modified (OMMT) ... more Nanocomposites containing polyethylene (PE) and montmorillonite clay organically modified (OMMT) with quaternary ammonium salts were obtained via direct melt intercalation. A montmorillonite sample from the Brazilian state of Paraíba was treated with four different types of quaternary ammonium salts. After the treatment, the powder was characterized by X-ray diffraction and scanning electron microscopy. The dispersion and morphologies of OMMT within PE were investigated by X-ray diffraction and transmission electron microscopy. The results revealed the formation of intercalated montmorillonite layers in the PE matrix. The thermal stability and flammability of the PE/montmorillonite clay nanocomposites were measured by thermogravimetry and horizontal burning tests for HB classification, Underwrites Laboratories (UL 94), respectively. It was shown that the samples do not degrade at the processing temperature. By adding only 3 wt.% montmorillonite, the burning rate of the nanocomposites was reduced by 17%, and, in general, the tensile test showed that the yield strength and modulus of the nanocomposites are close to the pure PE. However, for a selected salt for MMT treatment the mechanical properties of nanocomposites were improved.
Sumário: 1 Introdução; 2 Um breve painel histórico acerca direito empresarial no Brasil; 2.1 A se... more Sumário: 1 Introdução; 2 Um breve painel histórico acerca direito empresarial no Brasil; 2.1 A separação do Direito brasileiro; 2.2 Tendências unificadoras no Brasil; 3 Desmistificando questões préconcebidas; 3.1 Empresa versus estabelecimento comercial; 3.2 Empresa versus firma; 3.3 Sociedade Empresária versus sociedade simples; 3.4 Atividade fim versus atividade meio 3.5 sociedade empresaria versus empresa: sujeito de direito e objeto de direito; 4. Noções fundamentais sobre o Direito empresarial brasileiro; 4.1 Empresa: noção jurídica e econômica; 4.2 O empresário comercial; 4.3 Pessoa jurídica e exceções; Conclusão; Referencial
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Papers by André Rodrigues