| Budget Amount *help |
¥16,740,000 (Direct Cost: ¥15,300,000、Indirect Cost: ¥1,440,000)
Fiscal Year 2007: ¥6,240,000 (Direct Cost: ¥4,800,000、Indirect Cost: ¥1,440,000)
Fiscal Year 2006: ¥10,500,000 (Direct Cost: ¥10,500,000)
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| Research Abstract |
Carbonyl sulfide (COS) is the most abundant sulfur compound in the atmosphere, with its tropospheric mixing ratios reported to be around 500 pptv. COS is regarded as a dominant source of stratospheric sulfate aerosol, which influences the earth's radiation budget, and then the climate. Therefore, attention is being focused on both sources and sinks of COS. Although sail microorganisms are known to play a role as a sink for atmospheric COS, little information is available on the quantification of microorganisms responsible for the COS degradation.
COS added to the liquid culture is abiotically degraded to carbon dioxide and hydrogen sulfide during incubation period, and co-metabolic transformation might be significant in the case of consumption of atmospheric trace gas. Therefore, MPN was diverted as follows: we counted MPN of chemoorganotrophic microorganisms first, then presence of the COS-degrading microbes were confirmed by using the culture of the MPN. COS gas was added to each cult
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ure after 1-2 week's incubation of MPN for chemoorganotrophs, and COS decrease was monitored by FPD-GC.
Densities of chemoorganotrophs and COS degraders were 1.0 x 10^7 and 3.5 x 10^6 MPN/g d. w., respectively, in a forest soil which degraded 30 ppmv of COS in one hour, indicating that COS degraders accounted for the large part of chemooarganotrophic microorganisms. Comparative 16S rRNA gene sequence analysis indicated that these isolates belonged to the genera Mycobacterium, Williamsia and Cupriavidus. For example, Mycobacterium sp. strain THI401, grown on PYG agar medium, was able to degrade an initial 30 ppmv COS within one hour, while 60% of the initial COS was decreased by abiotic conversion in 30 hours. Considering natural COS flux between sail and the atmosphere, COS degradation by these bacteria was confirmed at an ambient level of 500 pptv using sterilized soil to cultivate the bacterium: Strain THI401 degraded COS from an initial level of 530 pptv to a level of 330 pptv in 30 hours. These results provide experimental evidence of microbial activity in soil as a sink for atmospheric COS. By using crude extract of strain THI401, COS hydrolase was purified to 17 fold of the original by column chromatography. COS hydrolase has been purified from Thiobacillus thioparus THI115, a chemolithoautotrophic COS degrading bacterium. Cloning of the gene was conducted based on the amino acid sequence data of N-terminal COS hydrolase, and open reading flame of 660 by was determined. COS hydrolase is found to be encoded by a single gene in strain THI115. Less
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