Phylogenetic, Microbiological, and Glycoside Hydrolase Diversities within the Extremely Thermophilic, Plant Biomass-Degrading Genus Caldicellulosiruptor

Abstract

Phylogenetic, microbiological, and comparative genomic analyses were used to examine the diversity among members of the genus Caldicellulosiruptor, with an eye toward the capacity of these extremely thermophilic bacteria to degrade the complex carbohydrate content of plant biomass. Seven species from this genus (C. saccharolyticus, C. bescii, C. hydrothermalis, C. owensensis, C. kronotskyensis, C. lactoaceticus, and C. kristjanssonii) were compared on the basis of 16S rRNA gene phylogeny and cross-species DNA-DNA hybridization to a whole-genome C. saccharolyticus oligonucleotide microarray, revealing that C. saccharolyticus was the most divergent within this group. Growth physiology of the seven Caldicellulosiruptor species on a range of carbohydrates showed that, while all could be cultivated on acid-pretreated switchgrass, only C. saccharolyticus, C. bescii, C. kronotskyensis, and C. lactoaceticus were capable of hydrolyzing Whatman no. 1 filter paper. Twodimensional gel electrophoresis of the secretomes from cells grown on microcrystalline cellulose revealed that the cellulolytic species also had diverse secretome fingerprints. The C. saccharolyticus secretome contained a prominent S-layer protein that appears in the cellulolytic Caldicellulosiruptor species, suggesting a possible role in cell-substrate interactions. Growth physiology also correlated with glycoside hydrolase (GH) and carbohydrate-binding module (CBM) inventories for the seven bacteria, as deduced from draft genome sequence information. These inventories indicated that the absence of a single GH and CBM family was responsible for diminished cellulolytic capacity. Overall, the genus Caldicellulosiruptor appears to contain more genomic and physiological diversity than previously reported, and this argues for continued efforts to isolate new members from high-temperature terrestrial biotopes.

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

“…Caldicellulosiruptor bescii is one of the few thermophilic bacteria reported to degrade crystalline cellulose (4,59). It is of interest, therefore, to understand the strategy and the enzymes used by this bacterium for this purpose, as the knowledge could be of industrial importance.…”

Identification and characterization of a multidomain hyperthermophilic cellulase from an archaeal enrichment

“…This limitation may give rise to more symbiotic relationships during cellulolytic growth at high temperatures. No archaeal cellulases from D. fermentans have been characterized to date but recently secretome and genome analysis showed several GHs coded by the bacterium C. bescii 21 . Given the limited success in finding single hyperthermophiles that can grow on crystalline cellulose, the discovery of hyperthermophilic cellulases may necessitate the broader application of enrichment driven metagenomics.…”

Complete Genome Sequences for the Anaerobic, Extremely Thermophilic Plant Biomass-Degrading Bacteria Caldicellulosiruptor hydrothermalis , Caldicellulosiruptor kristjanssonii , Caldicellulosiruptor kronotskyensis , Caldicellulosiruptor owensensis , and Caldicellulosiruptor lactoaceticus

“…With optimal growth temperatures ranging from 70 to 78°C, the genus Caldicellulosiruptor contains the most thermophilic microorganisms capable of biological cellulose hydrolysis known. While 16S rRNA phylogeny indicates a very close relationship within the eight species studied thus far (94.8% to 99.4% identity), microbiological analysis indicated that the genus is more physiologically divergent than previously thought (2). Three complete genome sequences are currently available for this genus, those of C. saccharolyticus (19), C. bescii (12), and C. obsidiansis (5), all of which are capable of crystalline cellulose hydrolysis.…”