Biology

Event Date: 
Wednesday, July 31, 2013 - 18:15 - 18:30
Institution: 
University of Technology Sydney
Title: 

The Sydney Harbour microbiome: bacterioplankton diversity and dynamics

Abstract: 

Sydney Harbour and its surrounding coast is an iconic habitat that supports a diverse ecosystem however the composition and dynamics of bacterioplankton in the system remain a major knowledge gap. The harbour and coast also provide a model system for investigating the spatiotemporal distribution of microorganisms across multiple physicochemical gradients and their response to anthropogenic input. Using next-generation DNA sequencing, we provide a comprehensive profile of microbial communities from a range of habitats inside the harbour and show strong biogeographic patterns in taxonomic composition.  Using network analysis to visualize correlations between community structure and environmental variables we have identified the key drivers of community partitioning. Combined these results lead to a more detailed understanding of the diversity and roles of bacterioplankton in Sydney Harbour and its surrounds, and provide insight into marine microbial ecology generally. 

Event Date: 
Wednesday, July 31, 2013 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Genome evolution in Blattabacterium cuenoti

Abstract: 

In addition to harbouring intestinal symbionts, some animal species also possess intracellular symbiotic microbes. The relative contributions of gut-resident and intracellular symbionts to host metabolism, and how they coevolve are not well understood. Cockroaches and the termite Mastotermes darwiniensis present a unique opportunity to examine the evolution of spatially separated symbionts, as they harbour gut symbionts and the intracellular symbiont Blattabacterium cuenoti. The genomes of B.cuenoti from M.darwiniensis and the social wood-feeding cockroach Cryptocercus punctulatus are each missing most of the pathways for the synthesis of essential amino acids found in the genomes of relatives from non-wood-feeding hosts. Hypotheses to explain this pathway degradation include: (i) feeding on microbes present in rotting wood by ancestral hosts; (ii) the evolution of high-fidelity transfer of gut microbes via social behaviour. To test these hypotheses, we sequenced the B.cuenoti genome of a third wood-feeding species, the phylogenetically distant and non-social Panesthia angustipennis.We show that host wood-feeding does not necessarily lead to degradation of essential amino acid synthesis pathways in B.cuenoti, and argue that ancestral high-fidelity transfer of gut microbes best explains their loss in strains from M.darwiniensis and C.punctulatus.
 

Event Date: 
Wednesday, June 26, 2013 - 18:15 - 18:30
Institution: 
UWS
Title: 

How to dismantle a “Trichy” parasite: Deciphering the role Tritrichomonas foetus membrane and secreted proteins play at the host-parasite interface.

Abstract: 

 
Tritrichomonas foetus is a potent veterinary pathogen, causing bovine and feline trichomoniasis. While T. foetus is well know as a venereal pathogen of cattle, it has only recently been discovered as a pathogen of cats in which it causes chronic diarrhea. T. foetus imposes significant economic losses on the beef and dairy industries worldwide. Nonetheless, despite its prevalence, T. foetus is neglected relative to other parasites of veterinary concern. There is currently no effective treatment or vaccine and prevention of infection in cattle and relies on culling infected animals. Chemotherapy in cats is limited and, depending on the country, is either not recommended or prohibited due to limited efficacy and toxicity. These extracellular parasites secrete a range of molecules that aid in tissue destruction, nutrient acquisition and immune-evasion. Proteins expressed at the host-parasite interface (i.e. secreted and membrane proteins) are critical to promoting parasite development and survival. Our central hypothesis is that these key molecules, which mediate infections caused by T. foetus, present a target for the rational design of future treatment and control strategies.

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.

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, April 24, 2013 - 19:15 - 20:00
Institution: 
University of Technology Sydney
Title: 

Observing the developing infant gut microbiome with time-series metagenomics.

Abstract: 

The human body plays host to a complex microbial ecosystem, the
development of which begins around the time of birth. Routine monitoring
of the development of microbial ecosystems in newborns (or other
environments) using metagenomic methods is currently extremely
challenging and expensive. I will describe some recent technological
advances that could enable routine sequencing and computational analysis
of hundreds of metagenomes, and demonstrate their application on samples
taken from a developing infant gut microbiome. In this study forty-five
samples were subjected to transposon-catalyzed Illumina library prep and
metagenomic sequencing on a HiSeq 2000 instrument. The resulting data
was subjected to analysis of microbial community structure using a new
approach called phylogenetic Edge Principal Component Analysis (Edge
PCA) that can identify which lineages in a phylogeny explain the
greatest degree of variation among the samples. We also investigate the
population genomics of Bacteroides thetaiotaomicron, one of the dominant
members of the gut microbial community.

Event Date: 
Wednesday, April 24, 2013 - 18:15 - 18:30
Institution: 
University of Western Sydney
Title: 

Comparative Analysis Of Saxitoxin-Producing And Non-Toxic Ecotypes Of Anabaena circinalis

Abstract: 

During bloom events, freshwater cyanobacteria often produce a variety of harmful toxins with devastating health, environmental and economic consequences. The paralytic shellfish toxins are a large group of neurotoxic alkaloids including saxitoxin (STX), which is the most potent identified to date. In Australia, STX production is strain dependent within the cyanobacterium Anabaena circinalis. The following study utilised two strains of cyanobacteria, A. circinalis AWQC131C (131C) and A. circinalis AWQC310F (310F), as model organisms; 131C is a saxitoxin-producer whilst 310F serves as a non-toxic control. We aimed to characterise 131C and 310F at the genomic and proteomic levels using genome sequencing and isobaric tags for relative and absolute quantitation (iTRAQ), respectively, in order to identify key differences in not only their secondary but, primary metabolic pathways.
 
Draft genome sequencing of 131C and 310F revealed a genome length of 4.4 Mbp and a GC content of 37%, and the number of encoded genes was predicted to be 4447 and 4443 for 131C and 310F, respectively. A scan of each genome revealed a total of 740 unique coding regions within 131C, and 651 within 310F. Interestingly, the proteomic profile of 131C was significantly different from 310F. Using iTRAQ, we found that under standard laboratory conditions, 131C was highly abundant in photosynthetic and metabolic proteins compared to the non-toxic control.  This suggests a high C:N ratio and intracellular 2-oxoglutarate concentration and may be a novel site for posttranslational regulation of STX. Overall, 131C is potentially a high energy ecotype likely to inhabit the water surface. Conversely, 310F was more abundant in molecular chaperones and proteins that neutralise reactive oxygen species, indicating activation of cellular stress response. Therefore, 310F seems to be experiencing cellular stress under laboratory conditions and in the environment, may inhabit low-light areas below the water surface.
 
In conclusion, this study has provided an insight into fundamental differences between the toxic 131C and non-toxic 310F strains of A. circinalis. These findings will provide a platform for future experiments and hopefully pave the way to identify the cellular function of STX.

Event Date: 
Wednesday, April 24, 2013 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Domesticating E. coli

Abstract: 

Adaptation of environmental bacteria to laboratory conditions can lead to modification of important traits, what we term domestication. Little is known about the rapidity and reproducibility of domestication changes, the uniformity of these changes within a species or how diverse these are in a single culture. We analysed phenotypic changes in nutrient-rich liquid media or on agar of four E. coli strains newly isolated through minimal steps from different sources. The laboratory-cultured populations showed changes in metabolism, morphotype, fitness and in phenotypes associated with the sigma factor RpoS. Domestication events and phenotypic diversity started to emerge within 2-3 days in replicate sub-cultures of the same ancestor. In some strains, increased amino acid usage and higher fitness under nutrient limitation resembled those in mutants with the GASP (Growth Advantage in Stationary Phase) phenotype. The domestication changes are not uniform across a species or even within a single domesticated population. However, some parallelism in adaptation within repeat cultures was observed. Differences in the laboratory environment also determine domestication effects, which differ between liquid and solid media or with extended stationary phase. Important lessons for the handling and storage of organisms can be based on these studies.

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