Cost-effective xylanase production from free and immobilized Bacillus pumilus strain MK001 and its application in saccharification of Prosopis juliflora

Cultural conditions for xylanase production by an alkalophilic Bacillus pumilus strain MK001 were optimized under submerged fermentation. An initial medium pH 9.0, agitation 200 rpm, inoculum size 1.25% (v/v) and inoculum age 2 h were found to be optimal for maximum enzyme production. The bacterium secretes high levels of xylanase on agricultural residues (wheat bran 1220.0 IU ml(-1); wheat straw 900.0 IU ml(-1)) as well as on synthetic xylans (birch wood xylan 1190 IU ml(-1); oat spelt xylan 1150.0 IU ml(-1)). Among different inorganic/organic nitrogen sources tested, a combination of yeast extract and peptone (0.66% N-2 equivalent) produced maximum (1288.0 IU ml(-1)) xylanase titers. Among various amino acids. vitamins and surfactants, DL-beta-phenylalanine, niacin, and polyethylene glycol (PEG)-3330 maximally enhanced xylanase production by 136.0% (2880.0 IU ml(-1)), 79.0% (2190.0 IU ml(-1)), and 107% (2536.0 IU ml(-1)) respectively. Batch fermentation in 5-1 laboratory fermentor allowed reduction (8.0 h) in incubation period for optimal (2886.0 IU ml(-1)) xylanase production. Whole-cell immobilization of B. pumilus strain MK001 on inert supports (polyurethane foam. PUF and scotch brite, SB) was found to be superior in maximizing xylanase production (up to 4000.0 IU ml(-1)) as compared to natural supports (cotton and silk) (up to 3854.0 IU ml(-1)). Saccharification of chemically pretreated Prosopis juliflora by enzymatic cocktail (xylanase, cellulase and cellobiase) resulted in release of reducing sugars (15.5 g g(-1) saccharification efficiency of 20.0%). Fermentation of saccharified hydrolysates by Pichia stiptis resulted in an ethanol yield of 0.36g g(-1). (C) 2007 Elsevier B.V. All rights reserved.