Isolation and characterization of novel cellulase genes from uncultured microorganisms in different environmental niches

Four different environmental DNA libraries were prepared from microbial consortium collected from forest soil, dung of elephant, cow rumen and rotted tree. Seven independent clones specifying cellulase activities (five endo-beta-1,4-glucanases and two beta-glucosidases) were isolated and identified. Sequence analysis of the retrieved genes revealed that the encoded products of these cellulase genes shared less than 50% identities and 70% similarities to cellulases in the databases. Domain analysis predicted that four endo-beta-1,4-glucanases conform to glycolsyl hydrolase family 5 (GHF 5) and one endo-beta-1,4-glucanase to glycosyl hydrolase family 9 (GHF 9), while both beta-glucosidases belong to glycolsyl hydrolase family 3 (GHF 3). Further sequence analysis indicated that although a solid affiliation could be made for the two endo-beta-1,4-glucanases to the typical ruminal microbe Prevotella ruminicola, the rest formed deep-branched lineages with no close relatives. The revelation of the phylogenetic novelty provided a snapshot on the great diversity of cellulases in these natural environments. (C) 2008 Elsevier GmbH. All rights reserved.