Greenhouse gases

Event Date: 
Wednesday, September 30, 2015 - 19:00 - 19:45
Institution: 
University of Southern California
Title: 

Microbial evolutionary surprises in the future ocean:  Long-term adaptation of marine nitrogen-fixing cyanobacteria to high CO2

Abstract: 

The globally-distributed marine cyanobacterium Trichodesmium plays a key role in ocean biogeochemical cycles, as it is a major source of newly fixed atmospheric nitrogen to marine food webs.  Trichodesmium N2 fixation rates have been shown to increase under expected future high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity, but its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. My lab has been carrying out a nearly decade-long experimental evolution study with Trichodesmium growing under selection by projected future elevated CO2 levels.  Unexpectedly, selection under high CO2 results in large increases in nitrogen fixation and growth rates that appear to be irreversible, even after adapted cell lines are moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained even after returning to the ancestral environment. These constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, up-regulation of cellular energetic pathways, elevated expression of non-coding intergenic DNA, and increased activity of a potentially regulatory DNA methyltransferase enzyme. Ongoing work in my lab is examining the consequences of multiple nutrient limitation interactions (iron and phosphorus) for the physiology, biochemistry and genetics of Trichodesmium adapted to growing in a more nutrient-limited, acidified future ocean environment.  
 

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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