Cellulose from plant cell wall components can be broken down by specialized enzymes, which are primarily found in cellulolytic microorganisms.
The main types of cellulase can be classified into endoglucanases and exoglucanases, although oxidative enzymes can also participate. These enzymes are often modular.
An analysis of ∼1,500 bacterial genomes listed in the Carbohydrate-Active Enzyme (CAZy) database shows that 38% of all sequenced bacterial genomes contain at least one enzyme involved in cellulose cleavage.
The bacteria that encode one cellulase or more can be divided into four categories: saprophytes that do not synthesize cellulose, cellulose-synthesizing saprophytes, cellulose-synthesizing non-saprophytes and those that are neither saprophytic nor cellulose producing.
The role of bacterial cellulases therefore appears to be far more diversified than simply breaking down plant cell wall cellulose.
Cellulolytic enzymes have been the subject of renewed interest owing to their potential role in the conversion of plant lignocellulose to sustainable biofuels. An analysis of ∼1,500 complete bacterial genomes, presented here, reveals that ∼40% of the genomes of sequenced bacteria encode at least one cellulase gene. Most of the bacteria that encode cellulases are soil and marine saprophytes, many of which encode a range of enzymes for cellulose hydrolysis and also for the breakdown of the other constituents of plant cell walls (hemicelluloses and pectins). Intriguingly, cellulases are present in organisms that are usually considered as non-saprophytic, such as Mycobacterium tuberculosis, Legionella pneumophila, Yersinia pestis and even Escherichia coli. We also discuss newly emerging roles of cellulases in such non-saprophytic organisms.
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F.M.M. was funded by La Fondation Infectiopole Sud, France. G.J.D. is a Royal Society Wolfson Research Merit Award recipient.
The authors declare no competing financial interests.
The multiple combinations of modules in bacterial cellulases (PDF 158 kb)
- Saprophytic lifestyle
Referring to the lifestyle of an organism that feeds on dead organic matter of plant origin.
Organisms that feed on wood.
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Medie, F., Davies, G., Drancourt, M. et al. Genome analyses highlight the different biological roles of cellulases. Nat Rev Microbiol 10, 227–234 (2012). https://doi.org/10.1038/nrmicro2729
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