Insights into plant biomass conversion from the genome of the anaerobic thermophilic bacterium Caldicellulosiruptor bescii DSM 6725

Abstract

Caldicellulosiruptor bescii DSM 6725 utilizes various polysaccharides and grows efficiently on untreated high-lignin grasses and hardwood at an optimum temperature of ∼80°C. It is a promising anaerobic bacterium for studying high-temperature biomass conversion. Its genome contains 2666 protein-coding sequences organized into 1209 operons. Expression of 2196 genes (83%) was confirmed experimentally. At least 322 genes appear to have been obtained by lateral gene transfer (LGT). Putative functions were assigned to 364 conserved/hypothetical protein (C/HP) genes. The genome contains 171 and 88 genes related to carbohydrate transport and utilization, respectively. Growth on cellulose led to the up-regulation of 32 carbohydrate-active (CAZy), 61 sugar transport, 25 transcription factor and 234 C/HP genes. Some C/HPs were overproduced on cellulose or xylan, suggesting their involvement in polysaccharide conversion. A unique feature of the genome is enrichment with genes encoding multi-modular, multi-functional CAZy proteins organized into one large cluster, the products of which are proposed to act synergistically on different components of plant cell walls and to aid the ability of C. bescii to convert plant biomass. The high duplication of CAZy domains coupled with the ability to acquire foreign genes by LGT may have allowed the bacterium to rapidly adapt to changing plant biomass-rich environments.

Biochemical and Mutational Analyses of a Multidomain Cellulase/Mannanase from Caldicellulosiruptor bescii

“…The bacterium has been demonstrated to ferment crystalline cellulose, xylan, and insoluble extracts of the bioenergy feedstock switchgrass (12). In corroboration with this finding, within the genome of C. bescii is a large gene cluster in which nine genes were predicted to encode enzymes that either degrade cellulose or hemicellulose (12).…”

“…Recently, the complete genome sequencing of a thermophilic cellulose-and xylan-degrading bacterium (59), Caldicellulosiruptor bescii (previously classified as Anaerocellum thermophilum) (58), was accomplished (GenBank accession number CP001393) (12,30). The bacterium has been demonstrated to ferment crystalline cellulose, xylan, and insoluble extracts of the bioenergy feedstock switchgrass (12).…”

Direct conversion of plant biomass to ethanol by engineered Caldicellulosiruptor bescii

“…S2) under the transcriptional control of the C. bescii S-layer protein (Cbes2303) promoter (P S-layer ). RNA profiling has shown that S-layer protein RNA is abundant throughout growth, suggesting that the promoter may be strong and constitutive (29). A rho-independent transcription terminator derived from a region immediately downstream of Cbes2303 was fused to the end of the adhE gene ( Fig.…”

Bacterial genomes: what they teach us about cellulose degradation

“…A number of genomes have been sequenced [57], and gene expression data was obtained during growth on cellulose [58]. The cellulase sets of Caldicellulosiruptor species are similar to the A. cellulolyticus set of cellulases.…”