Department of Biological Sciences, Tokyo Metropolitan University, Tokyo 192-0397, Japan.
Microbes Environ. 2012;27(3):293-9. doi: 10.1264/jsme2.me11348. Epub 2012 Mar 23.
Microbial mats containing the filamentous anoxygenic photosynthetic bacterium Chloroflexus aggregans develop at Nakabusa hot spring in Japan. Under anaerobic conditions in these mats, interspecies interaction between sulfate-reducing bacteria as sulfide producers and C. aggregans as a sulfide consumer has been proposed to constitute a sulfur cycle; however, the electron donor utilized for microbial sulfide production at Nakabusa remains to be identified. In order to determine this electron donor and its source, ex situ experimental incubation of mats was explored. In the presence of molybdate, which inhibits biological sulfate reduction, hydrogen gas was released from mat samples, indicating that this hydrogen is normally consumed as an electron donor by sulfate-reducing bacteria. Hydrogen production decreased under illumination, indicating that C. aggregans also functions as a hydrogen consumer. Small amounts of hydrogen may have also been consumed for sulfur reduction. Clone library analysis of 16S rRNA genes amplified from the mats indicated the existence of several species of hydrogen-producing fermentative bacteria. Among them, the most dominant fermenter, Fervidobacterium sp., was successfully isolated. This isolate produced hydrogen through the fermentation of organic carbon. Dispersion of microbial cells in the mats resulted in hydrogen production without the addition of molybdate, suggesting that simultaneous production and consumption of hydrogen in the mats requires dense packing of cells. We propose a cyclic electron flow within the microbial mats, i.e., electron flow occurs through three elements: S (elemental sulfur, sulfide, sulfate), C (carbon dioxide, organic carbon) and H (di-hydrogen, protons).
日本中宫温泉的丝状厌氧气光合细菌绿屈挠菌能够形成微生物席。在这些微生物席的厌氧条件下，提出硫酸盐还原菌作为硫化物的产生者与绿屈挠菌作为硫化物的消费者之间的种间相互作用构成了一个硫循环；然而，中宫温泉微生物硫化物生产所利用的电子供体仍有待确定。为了确定这种电子供体及其来源，探索了对微生物席进行的现场实验培养。在钼酸盐存在的情况下，它抑制了生物硫酸盐还原，从席样本中释放出氢气，表明这种氢气通常被硫酸盐还原菌用作电子供体消耗。在光照下，氢气的产生减少，表明绿屈挠菌也作为氢气的消费者。少量的氢气可能也被用于硫还原。从席中扩增的 16S rRNA 基因的克隆文库分析表明存在几种产氢发酵细菌。其中，最主要的发酵菌是炙热纤维菌，成功地被分离出来。该分离株通过有机碳的发酵产生氢气。微生物细胞在席中的分散导致在不添加钼酸盐的情况下产生氢气，这表明席中氢气的同时产生和消耗需要细胞的紧密堆积。我们提出了微生物席内的循环电子流，即电子流通过三个元素发生：S（单质硫、硫化物、硫酸盐）、C（二氧化碳、有机碳）和 H（二氢、质子）。
