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

Abstract

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.

Proliferation of diversified clostridial species during biological soil disinfestation incorporated with plant biomass under various conditions

“…Since the incorporation of plant biomasses to the soil strongly enhanced growth of clostridial species as shown by the clone library analysis, VFAs might be produced by these anaerobic bacteria through decomposition of the biomass. These results coincided with the results of our previous study (Mowlick et al 2012). As mentioned below, we have 26 already isolated many strains of anaerobic bacteria from both B. juncea-and wheat-bran-treated soil used in this study and confirmed formation of acetate and butyrate as fermentation products for many of the isolates (data not shown).…”

“…Besides, fatty acids like acetate or butyrate produced by these bacterial groups were supposed to contribute to pathogen inactivation (Momma et al 2006). These acids were actually detected in the BSD soil (Mowlick et al 2012), and it was strongly suggested that acetate, butyrate or other substances could be the products of the clostridial groups responsible for the suppression of some soil borne pathogens. Thus, it seems that proliferation of clostridial species in BSD treated soil may be important to make the treatment more effective.…”

“…were followed as described in the previous study (Mowlick et al 2012 Luria-Bertani (LB) plates by the standard methods (Kaku et al 2005). Sequence analysis (about 600 bp) was done for a total of 96 clones from each soil sample using a sequence primer U515f (5' GTG YCA GCM GCC GCG GTAA-3') according to the Dye Terminator method using a capillary sequencer at Takara Co. Ltd.…”

“…To compare with our previous results (Mowlick et al 2012), soil was obtained from a different district of Japan and a different pathogen was used in the experiment.…”

“…In a previous report, we analyzed the bacterial communities in soil of a BSD experiment using Brassica juncea plants or wheat bran (Mowlick et al 2012). The BSD treatment with these plant biomass successfully decreased the population of the pathogen (Fusarium oxysporum f. sp.…”