Cellulolytic activity of bacteria isolated and selected from paddy soil in Vinh Long province, Vietnam

Abstract

Importance of the work: The cellulose-degrading bacteria studied may be potential candidates to enhance the process of rice straw decomposition in rice cultivation. Objectives: To isolate and select thermotolerant bacterial isolates with cellulose–degrading activity to supplement the composting process of microbial organic fertilizer from rice straw. Materials and Methods: The cellulose-degrading ability of the bacterial isolates from the paddy soil samples was determined by staining carboxylmethylcellulose (CMC) plates with Congo red solution. The cellulose–degrading bacterial isolates were identified based on morphological and biochemical characteristics, the API 20E kit and 16S rRNA gene sequencing. Results: Overall, 28 of the 36 isolates were capable of degrading CMC with halo diameters ranging from 1.0 ± 0.0 to 10.0 ± 0.0 mm. The cellulose-degrading ability of isolate ĐRVL10 was highest at 40°C and pH 7.0. In particular, isolate ĐRVL10 had the ability to decompose cellulose at 45–55°C. The bacterial isolates had the ability to decompose rice straw after 15 d on tryptic soy broth (TSB) medium, with decomposition rates ranging from 23% to 63%, while on nutrient broth medium the range was 26%–53%. Based on the morphological and biochemical characteristics using the API 20E kit and 16S rRNA gene sequencing analysis, two bacterial isolates (ĐRVL7 and ĐRVL10) were identified as two different species in the genus Bacillus and Neobacillus, respectively. Main finding: The bacterial isolate had the ability to decompose at high temperature and also to decompose straw strongly under in vitro conditions.