Oral administration of hydrogen water ameliorates Parkinson’s disease (PD) in rats, mice, and humans. We previously reported that the number of putative hydrogen-producing bacteria in intestinal microbiota is low in PD compared to controls. We also reported that the amount of hydrogen produced by ingestion of lactulose is low in PD patients. The decreased hydrogen production by intestinal microbiota may be associated with the development and progression of PD. We measured the amount of hydrogen production using gas chromatography by seven bacterial strains, which represented seven major intestinal bacterial groups/genera/species. Blautia coccoides and Clostridium leptum produced the largest amount of hydrogen. Escherichia coli and Bacteroides fragilis constituted the second group that produced hydrogen 34- to 93-fold lower than B. coccoides. Bifidobacterium pseudocatenulatum and Atopobium parvulum constituted the third group that produced hydrogen 559- to 2164-fold lower than B. coccoides. Lactobacillus casei produced no detectable hydrogen. Assuming that taxonomically neighboring strains have similar hydrogen production, we simulated hydrogen production using intestinal microbiota that we previously reported, and found that PD patients produce a 2.2-fold lower amount of intestinal hydrogen compared to controls. The lower amount of intestinal hydrogen production in PD was also simulated in cohorts of two other countries. The number of hydrogen-producing intestinal bacteria may be associated with the development and progression of PD. Further studies are required to prove its beneficial effect.

Hydrogen (H2) is one of the most important intermediates in the anaerobic decomposition of organic matter. Although the microorganisms consuming H2 in anaerobic environments have been well documented, those producing H2 are not well known. In this study, we elucidated potential members of H2‐producing bacteria in a paddy field soil using clone library analysis of [FeFe]‐hydrogenase genes. The [FeFe]‐hydrogenase is an enzyme involved in H2 metabolism, especially in H2 production. A suitable primer set was selected based on the preliminary clone library analysis performed using three primer sets designed for the [FeFe]‐hydrogenase genes. Soil collected in flooded and drained periods was used to examine the dominant [FeFe]‐hydrogenase genes in the paddy soil bacteria. In total, 115 and 108 clones were analyzed from the flooded and drained paddy field soils, respectively. Homology and phylogenetic analysis of the clones showed the presence of diverse [FeFe]‐hydrogenase genes mainly related to Firmicutes, Deltaproteobacteria, and Chloroflexi. Predominance of Deltaproteobacteria and Chloroflexi suggests that the distinct bacterial community possessed [FeFe]‐hydrogenase genes in the paddy field soil. Our study revealed the potential members of H2‐producing bacteria in the paddy field soil based on their genetic diversity and the distinctiveness of the [FeFe]‐hydrogenase genes.

The transcription patterns of [FeFe]-hydrogenase genes (hydA), which encode the enzymes responsible for H2 production, were investigated during rice straw decomposition in paddy soil using molecular biological techniques. Paddy soil amended with and without rice straw was incubated under anoxic conditions. RNA was extracted from the soil, and three clone libraries of hydA were constructed using RNAs obtained from samples in the initial phase of rice straw decomposition (day 1 with rice straw), methanogenic phase of rice straw decomposition (day 14 with rice straw), and under a non-amended condition (day 14 without rice straw). hydA genes related to Proteobacteria, Firmicutes, Bacteroidetes, Chloroflexi, and Thermotogae were mainly transcribed in paddy soil samples; however, their proportions markedly differed among the libraries. Deltaproteobacteria-related hydA genes were predominantly transcribed on day 1 with rice straw, while various types of hydA genes related to several phyla were transcribed on day 14 with rice straw. Although the diversity of transcribed hydA was significantly higher in the library on day 14 with rice straw than the other two libraries, the composition of hydA transcripts in the library was similar to that in the library on day 14 without rice straw. These results indicate that the composition of active H2 producers and/or H2 metabolic patterns dynamically change during rice straw decomposition in paddy soil.

Changes in the relative abundances of the transcripts of hydA gene paralogs for [FeFe]-hydrogenase in Clostridium sp. strain H2 and Desulfovibrio sp. strain A1 isolated from paddy field soil were analyzed during H 2 production. Strains H2 and A1 had at least five and two phylogenetically different hydA genes, respectively. The relative abundances of their hydA transcripts differed among the paralogs and H 2 production activity changed in a manner that depended on the growth phase and conditions. Increases or decreases in the relative abundances of the transcripts of two out of five hydA genes in strain H2 correlated with changes in H 2 production rates, whereas those of the others remained unchanged or decreased. In strain A1, the relative abundances of the transcripts of two hydA genes differed between monoculture, sulfate-reducing, and syntrophic, methanogenic conditions. The relative abundance of the transcripts of one hydA gene, predicted to encode a cytosolic [FeFe]-hydrogenase, was higher under syntrophic, methanogenic conditions than sulfate-reducing conditions, while that of the transcripts of the other hydA gene decreased with time under both conditions. This study showed that the transcription of the hydA gene during growth with active H 2 production was differently regulated among the paralogs in H 2 producers isolated from paddy field soil.