May 2013

Event Date: 
Wednesday, May 29, 2013 - 19:00 - 19:45
Institution: 
CSIRO
Title: 

Sediment Biobarriers for Chlorinated Aliphatic Hydrocarbons in Groundwater Reaching Surface Water

Abstract: 

 
This study explored the potential of eutrophic river sediments to attenuate the infiltration of chlorinated aliphatic hydrocarbon (CAH)-polluted groundwater discharging into the Zenne River near Brussels, Belgium. Active biotic reductive dechlorination of CAHs in the riverbed was suggested by a high dechlorination activity in batch- and column biodegradation tests performed with sediment samples, and by the detection of dechlorination products in sediment pore water. Halorespiring Dehalococcoides spp. were present in large numbers in the riverbed as shown by quantification of their 16S rRNA and reductive dehalogenase genes. By using DGGE-fingerprint analysis of relevant nucleic acid markers, it was shown that the Zenne River sediments were inhabited by a metabolically diverse bacterial community. A large diversity of sulfate-reducing bacteria, Geobacteraceae and methanogens, which potentially compete with halorespiring bacteria for electron resources, was identified. The high organic carbon level in the top of the riverbed, originating from organic matter deposition from the eutrophic surface water, resulted in a homogeneous microbial community structure that differed from the microbial community structure of the sediment underneath this layer. Monitoring of CAH concentrations and stable isotope ratios of the CAHs (δ13C) and the water (δ2H and δ18O), allowed to identify different biotic and abiotic CAH attenuation processes and to delineate their spatial distribution in the riverbed. Reductive dechlorination of the CAHs was the most widespread attenuation process, followed by dilution by unpolluted groundwater discharge and by surface water-mixing. During a 21-month period, the extent of reductive dechlorination ranged from 27 to 89% and differed spatially but was remarkably stable over time, whereas the extent of abiotic CAH attenuation ranged from 6 to 94%, showed large temporal variations, and was often the main process contributing to the reduction of CAH discharge into the river. Although CAHs were never detected in the surface water, CAHs were not completely removed from the discharging groundwater at specific locations in the riverbed with high groundwater influx rates. Therefore, it was concluded that an increase in the extent of biotransformation in the riverbed is needed for acceptance of the Zenne biobarrier as a viable remedial option for attenuation of discharging CAH-polluted groundwater.

Event Date: 
Wednesday, May 29, 2013 - 18:15 - 18:30
Institution: 
Macquarie University
Title: 

Dissemination of antibiotic resistance determinants via sewage discharge from Davis Station, Antarctica

Abstract: 

Discharge of untreated or macerated sewage presents a significant risk to Antarctic marine ecosystems by introducing non-native microorganisms that potentially impact microbial communities and threaten health of Antarctic wildlife. Despite these risks, disposal of essentially untreated sewage continues in the Antarctic and sub-Antarctic. As part of an environmental impact assessment of the Davis Station, we investigated carriage of antibiotic resistance determinants in Escherichia coli isolates from marine water and sediments, marine invertebrates (Laturnula and Abatus), birds and mammals within 10 km of the Davis sewage outfall. Class 1 integrons typical of human pathogens and commensals were detected in 12% of E. coli isolates. E. coli carrying these integrons were primarily isolated from the near shore marine water column and the filter feeding mollusc Laturnula. Class 1 integrons were not detected in E. coli isolated from seal (Miroungaleonina, Leptonychotes weddellii) or penguin (Pygoscelis adeliae) feces. However, isolation of E. coli from these vertebrates’ faeces was also low. Consequently, sewage disposal is introducing non-native microorganisms and associated resistance genes into the Antarctic environment. The impact of this “gene pollution” on the diversity and evolution of native Antarctic microbial communities is unknown. 

 

Event Date: 
Wednesday, May 29, 2013 - 18:00 - 18:15
Institution: 
CSIRO
Title: 

Genotypic associations of Borrelia burgdorferi in mammalian and avian hosts

Abstract: 

Borrelia burgdorferi s. s., the bacterium that causes Lyme disease in North America, occurs as multiple co-circulating genotypes of the ospC gene, an important antigenic outer surface protein C. The diversity of ospC genotypes is thought to arise from fairly specific associations between genotypes and vertebrate hosts, such that different host species act as different “ecological niches” for the pathogen. To evaluate the degree of specificity of B. burgdorferi-host associations, we sampled genotypes of bacteria transmitted to ticks by several mammalian and avian host species. We also examined how the subset of genotypes known to infect humans, considered as human-invasive strains (HIS), is distributed among host species and higher taxonomic levels (birds, shrews, rodents). We adapted a patch occupancy model used for species detection to test for the occurrence probabilities (ψ) and transmission efficiencies (ε) associated with each ospC type. We found that the frequency of specific ospC genotypes varied among host species, demonstrating some support for the niche concept. Indeed, examination of all ospC types concurrently indicated that the ospC frequencies associated with birds and rodents were more similar within the taxonomic group than between groups based on principal components analysis. Conversely, HIS frequencies were more similar across all host species than within a host taxonomic level, implying weaker support for the niche concept. The occupancy model suggests that HIS types occurred more frequently than non-HIS types, but that HIS types generally had lower transmission efficiencies (from hosts to ticks). In several cases, rare genotypes had higher transmission efficiencies, suggesting an evolutionary trade-off between transmission efficiency and maintenance within the host. Our study highlights the importance of American robins (Turdus migratorius) and short-tailed shrews (Blarina brevicauda) in contributing large proportions of HIS types, and offers a novel way of examining occurrence and transmission efficiencies of ospC types within tick vectors, using a likelihood approach.