Xylanolytic and cellulolytic enzymes extracellular characterization on organic waste degrading bacteria

Abstract

Abstract. Ochieng OR, Njagi EN, Orinda GO, Otieno MF. 2019. Xylanolytic and cellulolytic enzymes extracellular characterization on organic waste degrading bacteria. Bioteknologi 16: 62-73. The disposal of untreated municipal waste is a global problem that challenges public and environmental health. In Kenya, composting, a microbial process with minimal environmental impact, has been given very little attention as an alternative waste treatment technology. Although bacteria can easily be genetically manipulated and therefore are good candidates for industrial use, very few have been researched. Furthermore, the optimum conditions for biodegrading solid wastes are not well understood. This study aimed at extracting and characterizing the biodegradative enzymes from 15 bacterial isolates obtained from dumpsite soil. The optimum period for extracellular enzyme production, pH, temperature, and the influence of selected ions on the activities of the enzymes was studied. The isolates were grown in four different growth media, and their enzymes were purified using ammonium sulphate precipitation. The substrate utilization pattern of the individual isolates was investigated using spectroscopic methods. Most of the isolates were bacterial of the genus bacillus. All the isolates were secreting extracellular proteins into their growth media. Most isolates had optimum protein production between 48-96 hours. Enzymes produced by most isolates were acting on all three commercial substrates (CM- cellulose, xylan, and cellobiose) [P>3.23 (F=3.88)]. Cellulases, xylanases and cellobioses had activities at broad temperature ranges 27^oC ([P< 3.23 (F=0.21)], 50^oC [P<3.23 (F=0.14)] and 80^oC [P<3.23 (F=0.06)], respectively). From the study, cellulases and cellobioses were acting within a large pH range (pH 4.8) (P> 3.23 (F=3.24] and (pH 6.8) [P>3.23 (F= 6.33)], respectively, while xylanases were acting within a narrow pH range (pH 4.8) [P< 3.23 (F=1.91]). Magnesium and calcium ions had a stimulatory effect on cellulases and cellobioses, while Silver and Copper ions inhibited the enzymes. Bacillus clausii (293), Bacillus sp. NER (117) and Bacillus sp. CSS-8 strain (108) had high activities on all the substrates and biodegrades at high pH and temperature ranges and can be used to facilitate biodegradation of waste when used with the correct ion concentration.