Papers by Wendy Williamson
Toxicon, 2015
The cyanobacterium Scytonema cf. crispum produces a range of saxitoxins. Previous studies on othe... more The cyanobacterium Scytonema cf. crispum produces a range of saxitoxins. Previous studies on other saxitoxin-producing cyanobacteria have shown that toxin production can vary throughout the growth cycle. Monitoring cyanotoxin-production in S. cf. crispum is challenging because it is metaphytic and has a very slow growth rate (ca. 6 months to reach stationary phase). In this study, a new method was developed to track growth and toxin production in S. cf. crispum. Samples were collected once a week for 131 days, and cell concentrations and saxitoxin quotas determined. Cells in the lag and exponential growth phases had significantly (P < 0.05) higher saxitoxin quotas (162 ± 37 fg cell(-1) and 139 ± 32 fg cell(-1), respectively) than the stationary phases (83 ± 19 fg cell(-1)). Extracellular saxitoxin concentrations were present at low concentrations (2-16 ng mL(-1) of culture medium) throughout the experiment. The proportion of extracellular saxitoxin to total saxitoxin decreased throughout the experiment. New knowledge on growth and saxitoxin variability will assist in improving monitoring, risk assessment and management of this species.
Water Science & Technology, 2011
This study determined whether human pathogenic viruses are present in two New Zealand surface wat... more This study determined whether human pathogenic viruses are present in two New Zealand surface waters that are used as drinking-water sources. Enteric viruses were concentrated using hollow-fibre ultrafiltration and detected using PCR for adenovirus (AdV), and reverse transcription PCR for norovirus (NOV) genogroups I-III, enterovirus, rotavirus (RoV) and hepatitis E virus (HEV). Target viruses were detected in 106/109 (97%) samples, with 67/109 (61%) samples positive for three or more viral types at any one time. AdV, NoV and ROV were detected the most frequently, and HEV the least frequently. Human NoV was not usually associated with animal NOV. Our results suggest that New Zealand would be well served by assessing the ability of drinking-water treatment plants to remove viruses from the source waters, and that this assessment could be based on the viral concentration of AdV-NoV-RoV. The long-term aim of our work is to use this information to estimate the risk of waterborne viral infection.
Soil Biological Fertility, 2004
... Wendy M. Williamson1 and David A. Wardle2 1 Landcare Research, PO Box 69, Lincoln, New Zealan... more ... Wendy M. Williamson1 and David A. Wardle2 1 Landcare Research, PO Box 69, Lincoln, New Zealand 2 Department of Animal & ... Edwards KJ, Bond PL and Banfield JF 2000 Characteristics of attachment and growth of Thiobacillus caldus on sulphide minerals: a chemotactic ...
Toxins, 2013
Studies on planktonic cyanobacteria have shown variability in cyanotoxin production, in response ... more Studies on planktonic cyanobacteria have shown variability in cyanotoxin production, in response to changes in growth phase and environmental factors. Few studies have investigated cyanotoxin regulation in benthic mat-forming species, despite increasing reports on poisoning events caused by ingestion of these organisms. In this study, a method was developed to investigate changes in cyanotoxin quota in liquid cultures of benthic mat-forming cyanobacteria. Iron and copper are important in cellular processes and are well known to affect growth and selected metabolite production in cyanobacteria and algae. The effect of iron (40-4000 μg L(-1)) and copper (2.5-250 μg L(-1)) on growth and anatoxin-a quota in Phormidium autumnale was investigated in batch culture. These concentrations were chosen to span those found in freshwater, as well as those previously reported to be toxic to cyanobacteria. Anatoxin-a concentrations varied throughout the growth curve, with a maximum quota of between...
Food and Environmental Virology, 2013
This article describes a rapid method for purifying infectious rotavirus particles from cell cult... more This article describes a rapid method for purifying infectious rotavirus particles from cell culture for environmental research. The method is based on size-exclusion chromatography using TOSOH TSKgel(®) G5000PWXL-CP with a TSKgel(®) Size Exclusion G2500PWxl guard column, set up on an AKTA Explorer10. Four peaks were identified from the chromatogram and the corresponding fractions were collected and analysed by electron microscopy, 1-step quantitative reverse transcription polymerase chain reaction (RT-PCR) and qNano measurement. Infectivity potential of the recovered virus particles was determined using cell culture. Our analysis reveals that the first fraction contains majority of the intact triple-layered infectious virions while the other three fractions contain mixtures of empty capsids and intact infectious virions. Our results also indicate that there is a gross overestimation of rotaviruses in crude extracts due to encapsidated RNA in the order of 2.3 × 10(11) particles and we note that estimates by qNano are similarly skewed (1.36 × 10(13) particle) possibly due to empty capsids and cellular debris. In summary we present a method for purification (~12 h) of rotaviruses for a more robust and accurate quantification of virus size, surface charge and particle concentration in environmental contexts.
Phycologia, 2012
ABSTRACT The recent identification of saxitoxin-producing Scytonema cf. crispum triggered a surve... more ABSTRACT The recent identification of saxitoxin-producing Scytonema cf. crispum triggered a survey of metaphyton and periphyton for Scytonema spp. in 34 high-use recreational lakes across Canterbury, New Zealand. Scytonema was observed in 10 of the lakes surveyed. Three morphospecies were identified: Scytonema cf. crispum, Scytonema cf. chiastum and Scytonema cf. fritschii. Environmental samples containing Scytonema were analysed for saxitoxins using the Jellett rapid test for paralytic shellfish poisoning, and saxitoxin variants were identified in positive samples using high-performance liquid chromatography with fluorescence detection (HPLC-FD). Cultures were established from selected sites and their phylogeny investigated using partial 16S rRNA gene sequences. These cultures were also screened for a region of sxtA, a gene involved in saxitoxin production. Cultures containing the sxtA gene were analysed for saxitoxins with HPLC-FD. Saxitoxins were only identified in cultures of S. cf. crispum and environmental samples containing this species. HPLC-FD analysis of these environmental samples and cultures identified saxitoxin and the variants gonyautoxins (GTX1-5), neosaxitoxin, decarbamoyl saxitoxin and decarbamoyl gonyautoxins (dcGTX2/3). This was the first report of these saxitoxin variants from cyanobacteria in New Zealand. All cultures of S. cf. crispum contained the sxtA gene segment. The partial 16S rRNA gene sequence of Scytonema C. Agardh ex Bornet & Flahault cultures were compared with cyanobacterial sequences from GenBank, only S. cf. fritschii clustered amongst other Scytonema species. The identification of metaphytic saxitoxin-producing S. cf. crispum highlighted a new freshwater habitat where toxic cyanobacteria may need to be monitored.
Veterinary Microbiology, 2009
Human norovirus (NoV) is reportedly the major cause of non-bacterial gastroenteritis outbreaks wo... more Human norovirus (NoV) is reportedly the major cause of non-bacterial gastroenteritis outbreaks worldwide and is commonly associated with water- and food-borne transmission via the faecal-oral route. Aside from humans, norovirus has been detected in pigs, cattle and mice. The close relatedness of some human and animal noroviruses has raised concerns about potential zoonotic transmission. Our laboratory recently reported the development of a multiplex real-time RT-PCR for the detection and genotyping of norovirus of genogroups I-III. Here we report a study of 56 faecal specimens from pigs and sheep that were collected and screened for noroviruses using this assay. Norovirus was found in 2/23 (9%) of porcine specimens (all were genogroup II) and in 8/33 (24%) of ovine specimens (all were genogroup III). Samples tested positive for norovirus were verified by conventional RT-PCR with different primer sets. Genomes of representative porcine and ovine norovirus strains underwent partial sequence analysis (343 and 2045 bases, respectively). This is the first report describing norovirus in sheep.
Soil Biology and Biochemistry, 2005
Following the creation of new land surfaces, there is an initial build-up phase, but in the prolo... more Following the creation of new land surfaces, there is an initial build-up phase, but in the prolonged absence of catastrophic disturbance an ecosystem decline phase has often been observed. While a number of studies have investigated the changes in soil biota that occur during the build-up phase, few studies have investigated how the soil food web changes during the ecosystem
Science, 2003
Although island attributes such as size and accessibility to colonizing organisms can influence c... more Although island attributes such as size and accessibility to colonizing organisms can influence community structure, the consequences of these for ecosystem functioning are little understood. A study of the suspended soils of spatially discrete epiphytes or treetop "islands" in the canopies of New Zealand rainforest trees revealed that different components of the decomposer community responded either positively or negatively to island size, as well as to the tree species that the islands occurred in. This in turn led to important differences between islands in the rates of ecosystem processes driven by the decomposer biota. This system serves as a model for better understanding how attributes of both real and habitat islands may affect key ecosystem functions through determining the community structure of organisms that drive these functions.
Oikos, 2005
... DA Wardle, WM Williamson and KI Bonner, Landcare Research, PO Box 69, Lincoln, New Zealand. D... more ... DA Wardle, WM Williamson and KI Bonner, Landcare Research, PO Box 69, Lincoln, New Zealand. DAW also at: Dept of Forest Vegetation Ecology, Swedish Univer-sity of Agricultural Sciences, SE 901-83 Umeå, Sweden ([email protected]). ...
Oikos, 2003
2003. The response of a three trophic level soil food web to the identity and diversity of plant ... more 2003. The response of a three trophic level soil food web to the identity and diversity of plant species and functional groups. -Oikos 102: 45 -56.
Oikos, 2004
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Journal of Microbiological Methods, 2006
We present the tellurite bioassay (Te-Assay) as an alternative approach for quantification of cel... more We present the tellurite bioassay (Te-Assay) as an alternative approach for quantification of cell viability. The Te-Assay was developed to pre-screen environmental samples for potential bacterial toxicants in which the reduction of tellurite to tellurium is used as a metabolic marker; black phenotype development only occurs in metabolically competent bacteria capable of reducing tellurite (TeO 3 2− ) to elemental tellurium. The black and white phenotypes equate to nonsignificant or significant impediment of normal metabolic processes, thus permitting the rapid visual assessment of the relative toxicity of environmental samples. Bacterial inocula were exposed in 96-well plates to arrays of diluted analytes or environmental samples before addition of a tellurite to assess cell health/viability. Toxicity was quantified as the analyte concentration at which a 50% reduction in blackness occurred (IC 50 ) compared to control wells containing no added analyte. No proprietary strains or reagents are required for Te-Assay, in which characterised strains or recent environmental isolates performed equally well. Strain selection was independent of tellurite-resistance provided that tellurite was reduced intracellularly by active non-growing cells.
Ground Water, 2012
This paper describes the in situ response of groundwater biofilms in an alluvial gravel aquifer s... more This paper describes the in situ response of groundwater biofilms in an alluvial gravel aquifer system on the Canterbury Plains, New Zealand. Biofilms were developed on aquifer gravel, encased in fine mesh bags and suspended in protective columns in monitoring wells for at least 20 weeks. Four sites were selected in the same groundwater system where previous analyses indicated a gradient of increasing nitrate down the hydraulic gradient from Sites 1 to 4. Measurements during the current study classified the groundwater as oligotrophic. Biofilm responses to the nutrient gradients were assessed using bioassays, with biomass determined using protein and cellular and nucleic acid staining and biofilm activity using enzyme assays for lipid, carbohydrate, phosphate metabolism, and cell viability. In general, biofilm activity decreased as nitrate levels increased from Sites 1 to 4, with the opposite relationship for carbon and phosphorus concentrations. These results showed that the groundwater system supported biofilm growth and that the upper catchment supported efficient and productive biofilms (high ratio of activity per unit biomass).
Ecology, 2008
There has been considerable recent interest in how human-induced species loss affects community a... more There has been considerable recent interest in how human-induced species loss affects community and ecosystem properties. These effects are particularly apparent when a commercially valuable species is harvested from an ecosystem, such as occurs through single-tree harvesting or selective logging of desired timber species in natural forests. In New Zealand mixed-species rain forests, single-tree harvesting of the emergent gymnosperm Dacrydium cupressinum, or rimu, has been widespread. This harvesting has been contentious in part because of possible ecological impacts of Dacrydium removal on the remainder of the forest, but many of these effects remain unexplored. We identified an area where an unintended 40-year "removal experiment" had been set up that involved selective extraction of individual Dacrydium trees. We measured aboveground and belowground variables at set distances from both individual live trees and stumps of trees harvested 40 years ago. Live trees had effects both above and below ground by affecting diversity and cover of several components of the vegetation (usually negatively), promoting soil C sequestration, enhancing ratios of soil C:P and N:P, and affecting community structure of soil microflora. These effects extended to 8 m from the tree base and were likely caused by poor-quality litter and humus produced by the trees. Measurements for the stumps revealed strong legacy effects of prior presence of trees on some properties (e.g., cover by understory herbs and ferns, soil C sequestration, soil C:P and N:P ratios), but not others (e.g., soil fungal biomass, soil N concentration). These results suggest that the legacy of prior presence of Dacrydium may remain for several decades or centuries, and certainly well over 40 years. They also demonstrate that, while large Dacrydium individuals (and their removal) may have important effects in their immediate proximity, within a forest, these effects should only be important in localized patches containing high densities of large trees. Finally, this study emphasizes that deliberate extraction of a particular tree species from a forest can exert influences both above and below ground if the removed species has a different functional role than that of the other plant species present.
Biological Invasions, 2010
Abstract Relatively few studies have considered how aboveground invasive consumers influence deco... more Abstract Relatively few studies have considered how aboveground invasive consumers influence decomposer communities. We investigated the poten-tial effects of three types of animals on the decom-poser subsystem in a floristically simple New Zealand Nothofagus forest. ...
Applied Soil Ecology, 2007
Applied and Environmental Microbiology, 2007
In this study, we developed a triplex real-time reverse transcription-PCR (RT-PCR)-based method t... more In this study, we developed a triplex real-time reverse transcription-PCR (RT-PCR)-based method that detects and distinguishes between noroviruses belonging to genogroups I, II, and III and that targets the junction between the regions of open reading frame 1 (ORF1) and ORF2. This is the first assay to include all three genogroups and the first real-time RT-PCR-based method developed for the detection of bovine noroviruses. The assay was shown to be broadly reactive against a wide spectrum of norovirus genotypes, including GI/1 through GI/7, GII/1 through GII/8, GII/10, GII/12, and GII/17, in different matrices (including fecal specimens, treated and raw sewage, source water, and treated drinking water). The assay is highly sensitive, detecting low copy numbers of plasmids that carry the target sequence. A new bovine norovirus, Bo/NLV/Norsewood/2006/NZL, was identified by this assay and was further genetically characterized. The results implicate a broad range of possible applications, including clinical diagnostics, tracing of fecal contaminants, and due to its sensitivity and broad reactivity, environmental studies.
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Papers by Wendy Williamson