Development of anaerobic bacterial community consisted of diverse clostridial species during biological soil disinfestation amended with plant biomass

Biological soil disinfestation (BSD) using plant biomass incorporation is an effective method and a good alternative to chemical fumigants for controlling soil-borne plant pathogens. In this study the bacterial communities in pot soil treated with three different BSD conditions (without plant biomass and with Brassica juncea L. plants or bran of wheat, Triticum aestivum L.) were analyzed using mainly molecular techniques. Earlier dropping of redox potential of both biomass-treated soils indicated rapid development of anaerobic conditions in the soil. The population of Fusarium oxysporum F. pathogen incorporated in the soil at the start was decreased considerably during the treatment, and the number of culturable anaerobic bacteria increased in both biomass-treated soils. Rather high concentrations of acetate and butyrate were detected from the biomass-treated soils. The polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis for the V3 region of 16S rRNA gene sequences revealed that the profiles of both biomass-treated soils were initially represented by similar and dominant groups, many of which were closely related to the species in the classes Clostridia and Bacilli of the phylum Firmicutes. Based on the clone library analysis, the control soil samples showed diverse bacterial groups with a few number of anaerobic clones. In contrast, for both biomass-treated libraries, clones belonging to the class Clostridia, a strictly anaerobic spore-forming bacterial group, appeared exceedingly dominant. The clostridial group detected was composed of phylogenetically diverse members, and it seemed likely that the diverse clostridial species were responsible for suppression of pathogens by making various compounds including volatile fatty acids and other compounds during anaerobic decomposition of plant biomass.