Characteristics of phototrophic purple bacteria isolated from a Japanese paddy soil

Phototrophic purple bacteria (PPB) were isolated from a Japanese paddy soil and their microbiological characteristics were then analyzed based on comparative morphology, chemotaxonomy, and comparison of 16S rDNA sequences. As a result, 18 strains of PPB were isolated, of which 17 strains were identified as Rhodopseudomonas palustris strains. The other was as a Rubrivivax gelatinosus strain. All the isolates showed a positive reaction in the acetylene reduction assay in the N-reduced medium. Effects of inoculation of the isolates into the soil slurries on soil acetylene-reducing activity (ARA) and methane (CH4) emissions from the slurries were examined using washed cells. The inoculated slurries showed a positive ARA reaction after 10-d incubation under illumination, unlike the control. CH4 emissions from the soil slurries 10 d after the inoculation of the isolates identified as Rps. palustris strains were significantly lower (44-62%) than those from the slurries without inoculants. These results suggest that PPB contribute to the enhancement of soil nitrogen fixation and mitigation of CH4 emissions from paddy soils.