Degradation of lignocellulosic content of rice straw using aerobic cellulolytic bacteria isolated from forest soil of Bangladesh

Abstract

The present research work was conducted to enumerate and isolate aerobic cellulolytic bacteria from forest soil using carboxymethyl cellulose (CMC) as substrate. The identified isolate was further tested as potent candidate to improve the nutritional value of rice straw. The forest soil was loaded with substantial amount (2.45×107) of cellulolytic bacteria. A total of 10 cellulose degrading bacteria (CDB) were isolated, identified and monitored for their cellulolytic activity. The isolate having the highest cellulolytic index (2.5) was identified as Bacillus subtilis targeting the 16S rRNA gene which was labeled as B. subtilis strain CDB7 and investigated for nutritional improvement of rice straw. Solid state fermentation of each group was carried out at 37°C for a period of 0, 3 and 6 days in 0 (no bacterial inoculum), 1, 5 and 10% inoculum group. There were a tendency of reduction in Acid Detergent Fiber (ADF), Neutral Detergent Fiber (NDF) and lignin at concentrations of 1, 5 and 10% inoculums at every interval of fermentation. Highest reduction of ADF (4.8%), NDF (10.78%) and lignin (37.6%) were observed after 6 days of fermentation at 10, 10 and 5% inoculum group, respectively. The crude protein content was increased (5.3 ± 0.4 to 6.4± 0.3) in 10% inoculum group. Taken together, the identified isolate could be a potent candidate to degrade lignocellulosic content through breaking of lignin-cellulose bondage and to improve the nutritional value of rice straw. Key words: Rice straw, Bacillus subtilis strain CDB7, solid state fermentation, acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin.