Genes that contribute to biomass deconstruction by members of the genus Caldicellulosiruptor

Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic microbes so far described and have the ability to digest lignocellulosic biomass without conventional pretreatment. The cellulolytic ability of different species varies dramatically and correlates with the presence of a number of enzymes that likely play an important role in biomass deconstruction. Among them is a multimodular cellulase CelA, which contains a glycoside hydrolase family 9 endoglucanase and a glycoside hydrolase family 48 exoglucanase known to be synergistic in their activity, connected by three cellulose-binding domains via linker peptides. This architecture exploits the cellulose surface revealing a novel paradigm for cellulase activity. A deletion of celA in C. bescii had a significant effect on its ability to utilize complex biomass and has been show to be modified post-translationally in its native host. The study of another cluster of genes, that encode pectinases, revealed that these enzymes play a surprising and unpredicted role in biomass deconstruction. These genes are highly up-regulated during growth on biomass, and a deletion of this gene cluster resulted in a dramatic reduction of the ability to grow on biomass in spite of the very low pectin content in poplar and switchgrass. Glycome profiling of the mutant implicated linkages to xylan in pectin release and this type of analysis may reveal as much about plant cell wall structure as biomass deconstruction.