Characterization Of Extracellular Cellulolytic And Xylolytic Enzymes From Organic Waste Degrading Bacteria

ABSTRACT

The disposal of untreated municipal wastes is a problem that challenges public and environmental health on global scale. In Kenya, the high population growth rates, urbanization and growth of the industrial sector have compounded the problem of environmental sustainability, notably, due to the large volumes of solid waste generated. The traditional dumping and land filling have been methods of choice for solid waste disposal for many municipalities; however, they lead to the pollution of the surrounding environment, have exorbitant costs associated with transporting waste and limited land resources suitable for these types of waste disposal. Despite all these limitations, 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 on. Furthermore, the optimum conditions under which they biodegrade solid wastes are not well understood. This study aimed at extracting and characterizing the biodegradative enzymes from 15 bacterial isolates obtained from dumpsite soil. Optimum period for extracellular enzyme production, pH, temperature and the influence of selected ions on the activities of the enzymes were studied. The isolates were grown in four different growth media and their enzymes 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. Majority of the isolates had optimum protein production between 48-96 hours. Enzymes produced by most isolates were acting on all the three commercial substrates (CMcellulose, xylan and cellobiose) [P>3.23 (F=3.88)]. Cellulases, xylanases and cellobiases had activities at broad temperature ranges 27oC ([P< 3.23 (F=0.21)], 50oC [P3.23 (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 stimulatory effect on cellulases and cellobiases 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.