College of Architecture and Environment, Sichuan University, No. 24, South Section 1, First Ring Road, Chengdu, Sichuan, 610065, China.
Institute of New Energy and Low-Carbon Technology, Sichuan University, No. 24, South Section 1, First Ring Road, Chengdu, Sichuan, 610065, China.
Sci Rep. 2019 Nov 22;9(1):17396. doi: 10.1038/s41598-019-53849-0.
Propionate is one of the most important intermediates of anaerobic fermentation. Its oxidation performed by syntrophic propionate-oxidizing bacteria coupled with hydrogenotrophic methanogens is considered to be a rate-limiting step for methane production. However, the current understanding of SPOB is limited due to the difficulty of pure culture isolation. In the present study, two anaerobic chemostats fed with propionate as the sole carbon source were operated at different dilution rates (0.05 d and 0.15 d). The propionate- and acetate-oxidizing bacteria in the two methanogenic chemostats were investigated combining DNA-stable isotope probing (DNA-SIP) and 16S rRNA gene high-throughput sequencing. The results of DNA-SIP with C-propionate/acetate suggested that, Smithella, Syntrophobacter, Cryptanaerobacter, and unclassified Rhodospirillaceae may be putative propionate-oxidizing bacteria; unclassified Spirochaetaceae, unclassified Synergistaceae, unclassified Elusimicrobia, Mesotoga, and Gracilibacter may contribute to acetate oxidation; unclassified Syntrophaceae and Syntrophomonas may be butyrate oxidizers. By DNA-SIP, unclassified OTUs with 16S rRNA gene abundance higher than 62% of total Bacteria in the PL chemostat and 38% in the PH chemostat were revealed to be related to the degradation of propionate. These results suggest that a variety of uncultured bacteria contribute to propionate degradation during anaerobic digestion. The functions and metabolic characteristics of these bacteria require further investigation.
丙酸是厌氧发酵最重要的中间产物之一。其被同型产乙酸菌与产氢甲烷菌共代谢氧化被认为是产甲烷的限速步骤。然而，由于纯培养分离困难，目前对 SPOB 的了解有限。本研究采用以丙酸为唯一碳源的 2 个厌氧恒化器，在不同稀释率（0.05 d 和 0.15 d）下运行。通过 DNA 稳定同位素探针（DNA-SIP）和 16S rRNA 基因高通量测序结合，研究了 2 个产甲烷恒化器中的丙酸和乙酸氧化菌。用 C-丙酸/乙酸进行 DNA-SIP 的结果表明，Smithella、Syntrophobacter、Cryptanaerobacter 和未分类的红螺菌科可能是潜在的丙酸氧化菌；未分类的螺旋体科、未分类的互营菌科、未分类的 Elusimicrobia、Mesotoga 和 Gracilibacter 可能有助于乙酸氧化；未分类的产烷菌科和产烷菌属可能是丁酸氧化菌。通过 DNA-SIP，PL 恒化器中总细菌的 16S rRNA 基因丰度高于 62%，PH 恒化器中高于 38%的未分类 OTU 与丙酸的降解有关。这些结果表明，多种未培养细菌有助于厌氧消化过程中丙酸的降解。这些细菌的功能和代谢特征需要进一步研究。
