Potential endoglucanase genes from the Red Sea Atlantis II brine pool: structure, organization and halophilic signature

Abstract

Cellulolytic enzymes have many industrial applications and play a major role in the process of biofuel production. Bioethanol is a cheap and clean alternative to non-renewable, polluting and expensive fossil fuel. Cellulases and hemicellulases act synergistically to degrade the cellulose polymer into glucose which can then be fermented by specific anaerobic organisms into ethanol. The overall manufacturing process occurs under harsh conditions such as low pH, high temperature and in the presence of elevated salt concentrations. The Atlantis II brine pool in the Red Sea is a unique habitat in terms of its diverse microbial community and physical conditions; high temperature of 68°C, almost saturating salt concentration of 270 psu, anoxia, pH 5.23 and depth of 2200 meters. Thus, finding cellulolytic enzymes from microbes adapted to these extreme conditions, whether they are cultivable or not, can contribute to cost reduction of bioethanol production. We mined 454 sequences from an Atlantis II metagenomic whole genome shotgun library for potential cellulolytic enzymes coding sequences of the Glycosyl Hydrolase 5 (GH-5) family and designed probes accordingly to screen for such genes in an Atlantis II fosmid library. We identified two positive fosmid clones that upon further sequencing and computational analysis were shown to have β-mannan hydrolyzing enzymes. They lack a CBD (cellulose binding domain) similar to non-modular cellulases from known cellulolytic microbes. They are predicted to be extracellular and secreted through the non-classical pathway. They have the 2 glutamic acid residues characteristic of the catalytic domain and possess a halophilic signature of salt adaptation.