| Date |
Feb 2nd, 2016 |
| Speaker |
PhD student Yohei Kumagai, Microbiology Lab., Atmosphere Ocean Institute, the University of Tokyo, Japan
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| Title |
Different adaptive strategies of photoheterotrophic and heterotrophic marine Flavobacteria
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| Abstract |
Proteorhodopsin (PR) is a photoreceptor membrane protein that acts as a light-driven proton pump and converts light
energy to proton motive force (PMF). PR-mediated H+ translocation provides sufficient PMF for ATP generation. Recent
culture-independent surveys show that PR gene occurs up to 80% of prokaryotes and expression level of PR is high in both
the RNA and the protein level in marine photic zone. Besides, PR-mediated photoheterotrophy is broadly distributed among
various groups of marine prokaryotes, in which alphaproteobacteria, gammaproteobacteria and Flavobacteria are a major
PR-possessing group in the ocean. Culture dependent studies showed that the growth rate of photoheterotrophic PR-
containing (PR+) marine Flavobacteria is stimulated by light. Moreover, recent researches revealed marine Flavobacteria
have many genes involved in anaplerotic inorganic carbon fixation and the carbon fixation activity is coupled with PR
expression. These results indicate that PR+ Flavobacteria can utilize light for both of generating energy and anabolic
processes and they are well adapted to the marine photic zone. On the other hand, it is noteworthy that heterotrophic PR-
not-containing (PR-) Flavobacteria are also widespread in photic zone. The coexistence of PR+ and PR- Flavobacteria
strongly suggests that those two groups have adopted different strategies to adapt to photic zones. To characterize the
ecophysiological differences between PR+ and PR- Flavobacteria, we sequenced 21 flavobacterial genomes and conducted
a comparative genomic analysis of 76 flavobacterial genomes containing 35 PR+ strains and 41 PR- strains. As a result, we
detect several genetic characteristics between them and the implication of these differences will be discussed in connection
with their ecophysiological features in this seminar.
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