Bioinformatic analysis of glycoside hydrolases in the proteomes of mesophilic and thermophilic Actinobacteria

Petroleum fuels are finite and non-renewable and they pose a significant concern for global climate, sustainability, and international security [1]. Alternative renewable sources of energy are urgently needed to meet the current global challenges. Plants are the most abundant source of renewable carbon on Earth. Plant cell wall (lignocellulose) can be used for the production of renewable, sustainable, and environmentally -clean biofuels [2]. Lignocellulose is mainly composed of polymers of sugars (cellulose and hemicellulose) and phenolic units (lignin). While complex lignocellulose can be converted into liquid fuels thermo-chemically, biological transformation of lignocellulosic polysaccharides using microorganisms and microbial enzymes is an economical and environmentally benign process for sustainable production of biofuels [3,4]. Several microorganisms produce glycoside hydrolase enzymes such as cellulases and xylanases that break down cellulose and xylan (hemicellulose), respectively [5]. Efficient lignocellulose-degrading microorganisms and catalyticallysuperior cellulases and xylanases are of very high value in the bioconversion of lignocellulose into biofuels [6,7]. Actinobacteria are a phylum of Gram-positive bacteria that are found abundantly in soil [8]. They include some of the most prolific lignocellulose-degrading bacteria [9]. Actinobacteria include both mesophilic and thermophilic members. Many new Actinobacteria continue to be isolated and sequenced in bioprospecting studies aimed at identifying new biotechnological targets [10]. Growing number of completely sequenced genomes are being steadily deposited in public databases, which provide an expanding resource for discovering novel targets for biotechnology. Systematic bioinformatic mining of the genomes and predicted proteomes of sequenced Actinobacteria has the potential to reveal novel insights into lignocellulose-degrading enzymes for bioenergy applications [11].