Isolation and characterization of cellulolytic bacteria from Lubimbi hot springs in Binga, Zimbabwe

Abstract

Cellulolytic bacteria have gained worldwide interest due to their ability to secrete thermostable enzymes with multiple uses. In this study, cellulolytic bacteria were isolated from local hot springs on carboxymethyl cellulose (CMC) agar and screened using 0.1% Congo red. Strains LB-4, LB-6 and LB-8 were found to have high cellulolytic indices of 1.8, 2.0 and 1.5, respectively. These strains were preliminarily identified based on morphology, gram’s reaction, and biochemical characteristics. They were rod-shaped, stained blue and possibly belong to a genus of motile Bacillus. The isolates were further subjected to homology analysis of the 16S rRNA gene. BLAST search showed strains LB-4, LB-6 and LB-8 to be 99.13%, 98.26% and 98.91% identical to Bacillus subtilis, Bacillus sp., and Bacillus licheniformis in the NCBI GenBank, respectively. The cellulolytic activity of each strain was evaluated using submerged fermentation that was terminated by the dinitrosalicylic acid (DNS) method. The optimum cellulase activity of the bacteria strains were observed after 24 hr at pH 7 and 40ºC while utilizing 1% CMC as a carbon source and 1% yeast extract as a nitrogen source. It can be concluded that cellulolytic bacteria were screened and identified from Lubimbi hot springs and the cellulase activity of each strain was optimized for different fermentation conditions. These strains have potential use in the pre-treatment of crop residues for biogas production.