Abstract
A lignocellulose-degrading strain isolated from thermophilic compost was identified as Geobacillus stearothermophilus B5, and found able to secrete considerable amounts of enzymes at optimal temperature (60 °C) and pH (7.5). One circular contig of 3.37 Mbp was assembled from raw data, and 3371 protein-coding genes were predicted. Clusters of orthologous groups (COG) analysis revealed various genes with functions in polymeric substrate degradation, especially for Carbohydrate Active enZymes (CAZymes), such as glycoside hydrolases (GHs) and glycosyl transferases (GTs). Furthermore, the transcriptional responses of B5 at different temperatures—with rice straw provided as the sole carbon source—were analyzed. The results revealed that B5 could resist high temperature by upregulating heat shock proteins (HSPs), enhancing protein synthesis, and decreasing carbon catabolism. Briefly, B5 possesses the ability of lignocellulose degradation, and might be considered a potential inoculant for improving composting efficiency.
Highlights
Lignocellulosic biomass, which composed of cellulose, hemicellulose, and lignin, are the most widely distributed and renewable organic carbon source on the earth
The Congo red assay is a qualitative assay of reducing sugars and commonly used to estimate cellulolytic activity
In Geobacillus, the recN gene has been identified as the most robust marker for assigning new bacterial strains at the species level [21], and homology search revealed that strain B5 is a member of the genus Geobacillus, showing the highest similarity (99.71%) to G. stearothermophilus DSM 458
Summary
Lignocellulosic biomass, which composed of cellulose, hemicellulose, and lignin, are the most widely distributed and renewable organic carbon source on the earth. Much composting research has focused on fungi, such as Aspergillus, Trichoderma, and Penicillium, bacteria as components of cellulase production strategies has gradually attracted more research attention, due to their resistance to environmental extremes, rapid growth, and expression of multienzyme complexes [3]. These microbes can degrade complex organic substances by secreting high levels of extracellular hydrolytic enzymes into the environment under self-heating, moist, and aerobic environments [4]. Xylanase, β-glucosidase, and protease are the key enzymes associated with the composting process, which depolymerize cellulose, hydrolyze xylan, hydrolyze glucosides, and promote N-mineralization, respectively [5]
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