Bacterial chitin degradation—mechanisms and ecophysiological strategies

Abstract

Chitin is one the most abundant polymers in nature and interacts with both carbon and nitrogen cycles. Processes controlling chitin degradation are summarized in reviews published some 20 years ago, but the recent use of culture-independent molecular methods has led to a revised understanding of the ecology and biochemistry of this process and the organisms involved. This review summarizes different mechanisms and the principal steps involved in chitin degradation at a molecular level while also discussing the coupling of community composition to measured chitin hydrolysis activities and substrate uptake. Ecological consequences are then highlighted and discussed with a focus on the cross feeding associated with the different habitats that arise because of the need for extracellular hydrolysis of the chitin polymer prior to metabolic use. Principal environmental drivers of chitin degradation are identified which are likely to influence both community composition of chitin degrading bacteria and measured chitin hydrolysis activities.

Flavobacterium johnsoniae Chitinase ChiA Is Required for Chitin Utilization and Is Secreted by the Type IX Secretion System

“…Such synergy has been demonstrated for the chitinases of other bacteria (47). Variations in organization of the polymer strands in the ␣, ␤, and ␥ forms of crystalline chitin, variation in the degree of acetylation, and variations regarding the components complexed with chitin (proteins, polysaccharides, or inorganic materials) (35,48) may mean that no single enzyme or set of enzymes is ideally suited to efficiently digest all forms of chitin. Additional experiments will be needed to determine the entire complement of chitinolytic enzymes that allows optimal digestion and utilization of different forms of chitin by F. johnsoniae cells.…”

Genomic Potential for Polysaccharide Deconstruction in Bacteria

“…Across all strains, chitinases are observed in deep clusters, including members of Cytophaga, Flavobacterium, Actinomyces, and groups of Proteobacteria and Firmicutes. Also, the prevalence of genes for GH20, mostly encoding ␤-1,6-N-acetylglucosaminidase, suggests that, as described for cellulose (8), many lineages may opportunistically compete with chitin degraders for the degradation products (e.g., chitobiose) (38). The high prevalence of strains (e.g., Vibrio [42] and Serratia [43] strains) with the potential for chitin degradation highlights chitin as a key resource across ecosystems (i.e., marine and soil ecosystems) (44,45).…”

“…In nature, cellulose is associated with various polymers (e.g., xylan) in most plant materials (5). Starch and glycogen are found in many organisms and are also important carbon sources for many bacteria (37), whereas chitin produced by fungi and arthropods is present in many environments (38). Finally, dextran and fructan (i.e., inulin) are also frequently observed polymers.…”

A novel halo-alkali-tolerant and thermo-tolerant chitinase from Pseudoalteromonas sp. DC14 isolated from the Caspian Sea

“…Moreover, chitinases have attracted interest as biocontrol agents due to their ability to degrade chitin in the fungal cell wall and insect exoskeleton (Tsujibo et al 2003;Mostafa et al 2009). It has been estimated that the annual production of chitin in aquatic systems is roughly equal to 10 10 -10 11 metric tons (Beier and Bertilsson 2013). In spite of the continuous production of chitin in the marine ecosystems, there is a low level of chitin accumulation in these environments (Alldredge and Gotschalk 1990).…”