KIDA Kenji Kumamoto University, Faculty of Engineering, Professor, 工学部, 教授 (00195306)
MORIMURA Shigeru Kumamoto University, Graduate School of Science and Technology, Associate Professor, 大学院・自然科学研究科, 助教授 (20230146)
|Budget Amount *help
¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 2003 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Fiscal Year 2002 : ¥2,100,000 (Direct Cost : ¥2,100,000)
Acetate conversion pathways of methanogenic consortia in acetate-fed chemostats at dilution rates of 0.025 d^<-1> and 0.6 d^<-1> were investigated using ^<13>C-labeled acetates followed by gas chromatogram mass spectrometry (GC-MS) analysis of CH_4 and CO_2 produced. Non-aceticlastic syntrophic oxidation by acetate oxidizing syntrophs and hydrogenotrophic methanogens was suggested to occupy a primary pathway in total methanogenesis at the low dilution rate. In contrast, aceticlastic cleavage of acetate by aceticlastic methanogens was suggested to occupy a primary pathway in total methanogenesis at the high dilution rate.
Phylogenetic analyses of transcripts of the methyl coenzyme M reductase gene (merA) confirmed a significant number of transcripts of the genera Methanoculleus, hydrogenotrophic methanogen, and Methanosarcina, aceticlastic methanogen, were present in the chemostats at the low and high dilution rates, respectively. The mcrA transcripts of the genus Methanosaeta, aceticlas
tic methanogen, which dominated the population, were poorly detected at the both dilution rate due to the limited diversity coverage of the primers used. These results demonstrated that dilution rate could cause a shift in the primary pathway of acetate conversion to methane in acetate-fed chemostats.
The microbial communities of methanogenic consortia in propionate-fed chemostats at dilution rates of 0.01 and 0.3 d^<-1> were investigated using fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE) and 16S rDNA clone analysis. In the domain Archaea, microorganisms closely related to the genera Methanosaeta and Methanoculleus were shown to be predominant at the low dilution rate. In the domain Bacteria, a propionate-oxidizing syntroph Syntrophobacter was shown to be predominant. At the high dilution rate, microorganisms related to the genera Methnaosaeta, Methanoculleus, Methanospirillum were dominant in the domain Archaea. In the domain Bacteria, microorganisms related to the genus Desulfotomaculum were predominant. These results indicated that the microorganisms responsible for degradation of propionate were different by the dilution rates. Less