Stromatolite

Event Date: 
Wednesday, January 30, 2013 - 19:00 - 19:30
Institution: 
University of NSW
Title: 

Who’s doing what? A metaproteomic survey of Southern Ocean microbes near Antarctica.

Abstract: 

The ocean around Antarctica is not just cold, it’s also dark for a large part of the winter.  This means that carbon fixation by photosynthesis is inhibited during the polar winter.  We used metaproteomics to reconstruct the ecology of microbes at the surface of the Southern Ocean near the Antarctic Peninsula, for both winter and summer seawater samples.  Metagenomics (community genomics) tells us what kinds of genes are present.  Metaproteomics goes a step further and determines which proteins (including enzymes) are actively being produced by microbes within a community.  Therefore, we can use this approach to reconstruct microbial processes used for carbon fixation, nutrient acquisition, and other metabolic pathways.  We found that ammonia-oxidising archaea were dominant at the Southern Ocean in winter, with the detected proteins indicating that they had a major role in ‘dark’ (light-independent) carbon fixation at the surface.  In summer, by contrast, these autotrophic archaea were undetectable at the ocean surface, when photosynthesis by algae was the major route of carbon fixation.  SAR11 bacteria (Pelagibacter spp.) were prevalent in both winter and summer, and detected proteins indicate that ATP-dependent uptake was important for the acquisition of nutrients by these heterotrophs, including simple organic compounds such as amino acids and taurine.  Flavobacteria (especially Polaribacter) were more prevalent in summer, and the detected proteins show that these heterotrophic bacteria use exoenzymes to target complex biomolecules (polypeptides, polysaccharides) released from decaying algae.  Overall, metaproteomics of the Southern Ocean surface has allowed us to identify the similarities and differences between winter and summer microbial communities, as well as which particular nutrients are being targeted by individual groups of bacteria and archaea.

Metagenomics has been a hot topic at JAMS in 2011. Playing to this popular theme, Thomas Jeffries of the University of Technology, Sydney opened the final meeting for the year with his metagenomic analysis of taxonomic and functional patterns in South Australia's hypersaline Coorong Lagoon. Thomas and colleagues found shifts in the abundance of cyanobacteria and Archaea linked to a salinity and nutrient gradient along the lagoon, as well as a shift in the abundance of genes related to salinity tolerance and photosynthesis. Surprisingly, despite the extreme range of environmental factors within Coorong, they found these patterns were dwarfed when the lagoon samples were placed in a global context, which showed substrate - in this case, solid or fluid - had a greater influence on taxonomic profiles. Thomas's work shows the importance of scale in the relationship between a microbial community and its environment.

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.
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