Carbon fixation

Event Date: 
Wednesday, October 28, 2015 - 18:00 - 18:15
Institution: 
UNSW
Title: 

Key to living in the extreme desert soils of eastern Antarctica: a chemolithotrophic lifestyle

Abstract: 

Mitchell Peninsula is located at the south of the Windmill Islands, Eastern Antarctica. It is described as a nutrient poor, extreme polar desert and limited knowledge on the microbial diversity of  the soils in this area exists. We examined the microbial taxonomic composition and metabolic potential of Mitchell Peninsula soils  using 16S metagenomics and shotgun metagenomics. We found the site to be a potential biodiversity hotspot, containing a high abundance of Candidate Phyla WPS2 and AD3. Subsequently, differential binning was used to recover 23 draft genomes, including 3 genomes from WPS-2 and two from AD3.  Further analysis of the metagenome revealed a novel Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) gene to be abundant in the bacterial community, despite a lack of evidence for photosynthesis related genes. We believe that unlike many other Antarctic regions, chemolithautrophic carbon fixation via CBB cycle is the dominant carbon fixation pathway, hence this pathway is providing the key to survival is this very dry, hostile environment. 

Event Date: 
Wednesday, March 26, 2014 - 19:00 - 20:00
Institution: 
UTS, Australia
Title: 

Feeling Hot Hot Hot: Insights on thermal regulation of microbial carbon fixation and metabolism in a warming ocean

Abstract: 

Ocean warming is expected to affect marine microbial phototrophs directly by influencing their metabolism and capacity for photosynthesis as well as indirectly through altering the supply of resources needed for growth. In turn, changes in phototrophic community composition, biomass and size structure are expected to have cascading impacts on export production, food web dynamics and fisheries yields, as well as the biogeochemical cycling of carbon and other elements. As a result, temperature is a critical parameter in coupled climate-ocean models because it influences not only the magnitude, but also the direction of future ocean productivity.
 
This seminar presents data from several recent oceanographic voyages to suggest that the statistically significant relationships found between temperature and carbon fixation of contemporary ocean microbes is confounded by the availability of co-varying light and nutrient resources, and challenges the notion that satellite-derived sea surface temperature is a suitable proxy for tracking changes in upper ocean biogeochemical function. It will also present laboratory data which demonstrates that thermal selection of photosynthetic microbes (over >100 generations) results in phenotypic trait evolution and shifts in photosynthesis:respiration. Collectively, these data show non-linearity in metabolism of photosynthetic microbes in a warming ocean, pointing to increased variability of responses and potentially less predictability in models.

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.

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