October 2011

Event Date: 
Wednesday, November 30, 2011 - 18:00 - 18:15
Institution: 
University of Technology Sydney
Title: 

Metagenomic insights into microbial community control: From the global to the microscale.

Abstract: 

The recent application of next-generation DNA sequencing tools has provided a wealth of new information about the diversity of microbial life, however the ecological factors which determine spatial patterns in prokaryotic gene abundance remain elusive. Using metagenomics and high-throughput sequencing of taxonomic marker genes, we have demonstrated shifts in microbial taxonomy and function along a salinity and nutrient gradient in the Coorong lagoon, South Australia. Functionally, genes showing the greatest response to physiochemical variability are related to salinity tolerance and photosynthesis. Taxonomically, Cyanobacteria and Archaea showed the greatest shifts in abundance along the gradient. Despite this variability however, the overall signature of metagenomic profiles remained remarkably conserved between sampling sites, and when compared to metagenomes from diverse habitats clustered with diverse sediment and soil habitats, regardless of salinity. This data indicates that the substrate type of the sample, fluid or porous, is a fundamental determinant of patterns in microbial community function globally, regardless of local chemical conditions. Whilst microbial community structure is determined on varying global and local scales, as demonstrated by the above data, the behaviour of microorganisms is determined on the microscale, with individual cells responding to gradients in specific nutrients in a patchy ecosystem. Using novel in situ sampling devices, and next-generation DNA sequencing techniques, our future work will focus on describing the microscale interactions between cells and nutrients in the ocean and how this relationship relates to ocean scale biogeochemical processes within the Carbon, Nitrogen and Sulfur cycles.

Event Date: 
Wednesday, November 30, 2011 - 18:15 - 18:30
Institution: 
University of Sydney
Title: 

The fungal secretome and virulence: analysis of the proteins secreted by Cryptococcus gattii strains with different virulence profiles.

Abstract: 
Cryptococcus gattii is a ubiquitous environmental yeast-like fungus capable of causing disease in a wide range of animal hosts. In humans, disease progression begins after inhalation of the infectious propagule leading to infection of the lung. The infective yeast cells can then disseminate to the central nervous system, resulting in meningoencephalitis, which can be fatal if left untreated.

Closely related strains of C. gattii exhibit significantly different degrees of virulence in the mammalian host. Fungi utilize absorbtive nutrition and produce a range of secreted degrative enzymes, and as these may invoke a host response, the fungal secretome is likely to be very important in modulating the host-pathogen interaction. In this study, we compare the secretomes of two C. gattii strains, one categorized as hypervirulent (R265) and the other exhibiting low-level virulence (R272). C. gattii was grown under conditions designed to be as similar as possible to those encountered in vivo. Secreted proteins were captured from the culture supernatant by re-circulating across ProteominerTM beads using a closed peristaltic pump system. Concentrated protein was analysed via 1D nanoLC-MS/MS. A total of 27 proteins were identified with only four protein identifications being shared by both strains. The secretome of R265 primarily included uncharacterized proteins containing catalytic cores with roles in carbohydrate degradation as well as the antioxidant superoxide dismutase and a GTPase. R272 secreted a more diverse set of proteins including enolase and transaldolase, enzymes canonically involved in glycolysis and the pentose phosphate pathway respectively, but both also described as fungal allergens that bind IgE.

This work indicates that very different cohorts of proteins are secreted by closely related strains of C. gattii exhibiting different levels of virulence. By enhancing our understanding of the fungal secretome and unraveling these differences it may suggest novel therapeutic strategies or help devise diagnostic markers predicting for disease progression.
Event Date: 
Wednesday, November 30, 2011 - 19:15 - 20:00
Institution: 
UNSW
Title: 

Rocking the cradle of life: Functional complexity of modern stromatolites.

Abstract: 
One of the major challenges in science is to identify modern living systems that present unique opportunities to address fundamental questions in diverse fields ranging from microbiology, geology, evolution, chemical biology, functional genomics, and biotechnology. The living stromatolites of Shark Bay on the western coast of Australia represent such a system. The overarching aim of our research program is to comprehensively characterise the functional complexity of modern stromatolites, in particular the diversity, biogeochemistry, and key interactions of the microorganisms forming the Shark Bay stromatolites. Understanding modern stromatolite systems is of fundamental significance to shed light on the evolution of early microbial life and the impacts of these ecosystems on both past and present global nutrient cycling.

Shark Bay is notable for its living marine stromatolites, and is listed as a World Heritage Site. In addition to their established evolutionary significance, these stromatolites, located in a hypersaline environment, are an ideal biological system for studying survival strategies of microorganisms to a range of stresses and their metabolic cooperation with other microorganisms. To further our understanding of these geobiological structures, detailed analyses of associated microbial communities and their functional characteristics are crucial.

This presentation will summarise the platform of our work over the last several years, focusing on recent discoveries and how these have led to new research directions employing a range of cutting edge technologies. This includes a comprehensive study elucidating major microbial populations, novel organism characterisation, signature lipid profiles, adaptive mechanisms of novel stromatolite isolates, creating a detailed biogeochemical profile of living stromatolites, whole genome analyses, and mechanisms of communication in these systems.

Finally, from an educational perspective, an interactive virtual field trip is being developed that will be an invaluable tool for both future research and conservation. Through the application of a rational and integrated approach, this research has provided valuable insights into these evolutionally significant biological systems. We now know who the key microbial players are, and can use this knowledge to examine specific functional characteristics to take the research to the next level, utilising the new suite of techniques now revolutionising the field of environmental microbiology.

  1. Allen MA, et al. (2010) Lipid biomarkers in Hamelin Pool microbial mats and stromatolites. Org Geochem 41, 1207-1218.
  2. Leuko S, et al. (2011) Molecular assessment of UVC radiation-induced DNA damage repair in the stromatolitic halophilic archaeon, Halococcus hamelinensis. J Photochem Photobiol B: Biology 102, 140–145.
  3. Goh F, et al. (2011) Osmoadaptive strategies of the archaeon Halococcus hamelinensis isolated from a hypersaline stromatolite environment. Astrobiology 11, 529-536.

A keen crowd of about 35 braved the rain to attend the September JAMS, which this month was held within the more spacious setting of the 4th floor at the Australian Museum. This month’s presentations all had a marine flavour, with the audience enjoying three entertaining talks focussed on the community dynamics and biogeochemical capabilities of marine microorganisms.