Lignocellulolytic bacteria isolated from organic rice field soils for enzyme production using agricultural wastes: Screening, medium optimization, and co-culture

Abstract

Lignocellulolytic bacteria can degrade agricultural biomass and fungal cell walls. Organic agriculture intensively employs these microbes as biofertilizers and biocontrol agents. This study focused on isolating, screening, identifying, and optimizing enzyme production of the lignocellulolytic bacteria obtained from organic rice field soils for utilizing in organic farming. Here we have shown that the farming periods can alter the bacterial biodiversity in organic rice field soil by providing different nutrients. Paenibacillus polymyxa BTK01 and Bacillus subtilis BTK07, which were isolated from the preharvest soil, exhibited a high activity of mannanase (MNN) and xylanase (XLN). By optimizing the enzyme production, BTK01 and BTK07 were specifically productive in xylanase and mannanase, respectively, because of the induction of substrate-like carbon sources. Varying the type and concentration of nitrogen source revealed that mannanase production positively correlated to bacterial growth of both strains. Throughout the study, we used soybean meal as a nitrogen source with the nitrogen concentration of 0.144% (w/v), BTK01 was productive in xylanase when cultured in the medium comprised of 1.5% (w/v) rice straw (0.905 ± 0.016 U/mL), and BTK07 was efficient in mannanase production when cultured in the medium consisted of 1.0% (w/v) copra meal (0.440 ± 0.000 U/mL). The co-culture of BTK01 and BTK07 using the volume ratio of 1:10 could yield MNN and XLN to be 2.470 ± 0.013 and 0.906 ± 0.015 U/mL, respectively. This result demonstrates that Paenibacillus polymyxa BTK01 and Bacillus subtilis BTK07 can be useful and applicable for organic agriculture as biocontrol agents and biofertilizers.