Carbon

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, September 26, 2012 - 19:00 - 20:00
Institution: 
University of New South Wales
Title: 

Microbial methane formation and oxidation in abandoned coal mines

Abstract: 

 
Worldwide, mine gas is being used increasingly for heat and power production. About 7% of the annual methane emissions originate from coal mining. In abandoned coal mines, stable carbon and hydrogen isotopic signatures of methane indicate a mixed thermogenic and biogenic origin. The thermogenic methane is a reminder of geological processes, but its biogenic formation is still going on. Besides hard coal, possible sources for methane are large amounts of mine timber left behind after the end of mining.
Methanogenic archaea are responsible for the production of substantial amounts of methane. Mine timber and hard coal showed an in situ production of methane with isotopic signatures similar to those of the methane in the mine atmosphere. Long-term incubations of coal and timber as sole carbon sources formed methane over a period of 9 months. We directly unraveled the active methanogens mediating the methane release as well as the active bacteria potentially involved in the trophic network. Furthermore, we proved the presence of an active methanotrophic community. Directed by the methane production and oxidation, respectively, samples for DNA stable-isotope probing (SIP) coupled to subsequent quantitative PCR and DGGE analyses were taken from long term incubations over 6 months. The stable-isotope-labeled precursors of methane, [13C]acetate and H2-13CO2, and 13CH4 were fed to liquid cultures from hard coal and mine timber. Predominantly acetoclastic methanogenesis was stimulated in enrichments containing acetate and H2+CO2. The H2+CO2 was mainly used by acetogens similar to Pelobacter acetylenicus and Clostridium species forming acetate as intermediate and providing it to the methanogens. Active methanogens, closely affiliated to Methanosarcina barkeri, utilized the readily available acetate rather than the thermodynamical more favourable hydrogen. Furthermore, the activity of a distinct methane-oxidizing community is predominated of a member belonging to the type I methanotrophs similar to Methylobacter marinus that assimilated 13CH4 nearly exclusively. Thus, active methanotrophic bacteria are associated with the methanogenic microbial community that is highly adapted to the low H2 conditions found in the coal mines with acetate as the main precursor of the biogenic methane.

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