Genomic and transcriptome analyses of a thermophilic bacterium Geobacillus stearothermophilus B5 isolated from compost reveal its enzymatic basis for lignocellulose degradation

Abstract

Background Composting is a special global carbon cycle which sustains various microbes engendering the cellulose degradation. Studies have obtained substantial compost microbiomes, yet the expressions and functions of these lignocellulolytic enzymes remains obscure. Thus, the discovery of thermophilic microorganisms as considerable biochemical catalysts for biofuels is becoming more and more attractive.Results A lignocellulose degrading strain isolated from thermophilic compost was identified as Geobacillus stearothermophilus B5, which could secrete considerable enzymes at the optimal temperature (60°C) and pH (7.5). One single contig of 3.37 Mbp was obtained from raw data and 3371 protein-coding genes were predicted, and the clusters of orthologous groups (COG) analysis revealed various genes with function of polymeric substrates degradation, especially for abundant CAZymes including glycoside hydrolases (GH, 29%) and glycosyl transferases (GT, 36%). Furthermore, the transcriptional responses of B5 at different temperature by using rice straw as sole carbon sources were also analyzed, based on which the mechanism of lignocellulose degradation at high temperature was revealed that B5 could resist the heat by up-regulating the heat shock proteins (HSP) and then secrete various Carbohydrate-Active enzymes (CAZymes) to realize energy balance.Conclusions The comparative whole-genome along with transcriptome analysis indicated that G. stearothermophilus B5 owned the ability of lignocellulose degradation and could be considered as a potential inoculant in composting efficiency, thus are also valuable for the lignocellulosic bioenergy industry.