Biotechnological Potential of Bacterial Endoglucanase from Marine and Hypersaline Environments in Saccharification of Lignocellulosic Biomass Pre-Treated with Alkali or Ionic Liquid

Abstract In second-generation biofuel production, the recalcitrant plant biomass requires pretreatment prior to enzymatic hydrolysis. Pretreatment with alkali or ionic liquids (IL) such as 1-butyl 3-methyl immidazolium chloride ([Bmim][Cl]), are efficient but the residual salt in former, or IL in later process inhibits downstream enzymatic saccharification and thus require extensive washing. Recent studies have established IL tolerance by moderate halophilic bacteria being contributed by their general salt adaptation strategies. Objective of the present study is to examine whether the same holds true for their extracellular enzymes, and eventually select a few for future exploitation. In this direction, ten distinct endoglucanase positive (≥3 mm halo zone in congo-red cellulolytic assay) colonies were picked each from decomposed wood material of the hypersaline Sambhar Lake (SLW), in Rajasthan; and Bichitrapur (BPW) mangrove in Orissa. SLW and BPW samples had total salinities of 21.54% and 2.18%; and their isolates had optimum NaCl requirement of 10-15% and 1-5% respectively. The extracellular endoglucanase of SLW isolates were active in 5-25% NaCl but those from BPW remain active in only up to 5% NaCl. Interestingly, SLW endoglucanases also performed better in 10% and some even in 30% (v/v)[Bmim][Cl]. Endoglucanase secreted by two SLW isolates, identified by their 16S rRNA gene sequence as Salipaludibacillus sp. were effectively used for in situ enzymatic hydrolysis of both alkali and [Bmim][Cl] pretreated rice straw. However, endoglucanase from BPW isolate Salinicola sp. could hydrolyze seawater washed alkali-pretreated biomass thereby expanding their industrial applicability in coastal areas.