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.

Keywords: bacteria; chitin; cross-feeding; glycoside hydrolase; interactions; organic matter; particles.

Figure 1

Processes involved in chitin degradation. If deacetylation and deamination processes are very active, chitosan or possibly even cellulose-like molecules might be produced. GH, glycoside hydrolase family; GlcNAc, N-acetylglucosamine; GlcN, glucosamine; Glc, glucose.

Figure 2

Fate of possible chitin degradation intermediates and degradation products at the interface of the global N and C-cycles: during the first degradation steps chitin is cleaved into small organic molecules that can directly be reintegrated into cell material or mineralized and potentially removed from the system. GlcNAc, N-acetylglucosamine; GlcN, glucosamine; Glc: glucose.