The Genome Sequences of Cellulomonas fimi and “Cellvibrio gilvus” Reveal the Cellulolytic Strategies of Two Facultative Anaerobes, Transfer of “Cellvibrio gilvus” to the Genus Cellulomonas, and Proposal of Cellulomonas gilvus sp. nov

Abstract

Actinobacteria in the genus Cellulomonas are the only known and reported cellulolytic facultative anaerobes. To better understand the cellulolytic strategy employed by these bacteria, we sequenced the genome of the Cellulomonas fimi ATCC 484T. For comparative purposes, we also sequenced the genome of the aerobic cellulolytic “Cellvibrio gilvus” ATCC 13127T. An initial analysis of these genomes using phylogenetic and whole-genome comparison revealed that “Cellvibrio gilvus” belongs to the genus Cellulomonas. We thus propose to assign “Cellvibrio gilvus” to the genus Cellulomonas. A comparative genomics analysis between these two Cellulomonas genome sequences and the recently completed genome for Cellulomonas flavigena ATCC 482T showed that these cellulomonads do not encode cellulosomes but appear to degrade cellulose by secreting multi-domain glycoside hydrolases. Despite the minimal number of carbohydrate-active enzymes encoded by these genomes, as compared to other known cellulolytic organisms, these bacteria were found to be proficient at degrading and utilizing a diverse set of carbohydrates, including crystalline cellulose. Moreover, they also encode for proteins required for the fermentation of hexose and xylose sugars into products such as ethanol. Finally, we found relatively few significant differences between the predicted carbohydrate-active enzymes encoded by these Cellulomonas genomes, in contrast to previous studies reporting differences in physiological approaches for carbohydrate degradation. Our sequencing and analysis of these genomes sheds light onto the mechanism through which these facultative anaerobes degrade cellulose, suggesting that the sequenced cellulomonads use secreted, multidomain enzymes to degrade cellulose in a way that is distinct from known anaerobic cellulolytic strategies.

Cellulomonas sp. Isolated from Termite Gut for Saccharification and Fermentation of Agricultural Biomass

“…The genes for alcohol dehydrogenase (ADH) in C. fimi were observed to be more in number than the genes of ADHS of C. thermocellum and Z. mobilis, combined (Christopherson et al 2013). So, it was designed to study different end products, specifically the ethanol.…”

Bacterial genomes: what they teach us about cellulose degradation

“…A large number of Cellulomonas species are known for their ability to degrade cellulose, including Cellulomonas flavigena, C. fimi, Cellulomonas uda and Cellulomonas gelida [53]. In spite of their well-known ability to degrade cellulose, only two of these species have completed genomes, C. flavigena [54] and C. fimi [55]. Surprisingly, both strains possess the exact same combination of 12 potential cellulases.…”

“…C. flavigena has 11 potential cellulases with CBM domains, seven with CBM2, two with CBM2 and CBM3, and two with two CBM4 domains. The genome sequencing of Cellvibrio gilvus revealed the organism was actually a member of the cellulomonads [55]. C. gilvus, another prolific cellulose degrader, possesses a smaller set of cellulases than the other two Cellulomonas species; its genome contains nine potential cellulases: two GH5, four GH6, two GH9 and one GH48 (Supplementary Table E).…”

Cloning and Sequence Analysis of the Cellulase Genes Isolated from Two Cellulolytic Streptomycetes and Their Heterologous Expression in <i>Streptomyces lividans </i>

“…In fact, similarly to Trichoderma reesei [1] and cellulolytic actinobacteria, e.g. Thermobifida fusca [2,3] and Cellulomonas fimi [4], some streptomycetes secrete extracellular cellulases ; celA and celB genes from Streptomyces lividans 66 [5,6] and celA1 and celA2 genes from Streptomyces halstedii strain JM8 [7,8] were demonstrated to encode endoglucanases capable of hydrolyzing carboxymethyl cellulose (CMC). Meanwhile, Streptomyces reticuli produced a cellulase designated Avicelase, which shows cellulase activity to convert microcrystalline cellulose (Avicel) to cellobiose [9].…”