Unravelling the regulatory network behind chitin degradation in Serratia marcescens

Chitin degradation plays a crucial role in bacterial nutrient recycling and is performed by specialised, chitinolytic microorganisms such as Serratia marcescens, which is known to excel at this biological process. While its chitinolytic enzymes have been studied in detail, the underlying regulatory systems that allow such proficiency at chitin utilisation remain elusive. This review addresses different aspects of chitin degradation by Serratia marcescens. Together with a summary of the necessary enzymes and transport systems for extracellular chitin degradation, we focus on the strategies employed by Serratia marcescens for optimal use of different carbon sources in the presence of chitin. A complex, multi-layered, regulatory network results in 'bet-hedging', involving the formation of phenotypically bistable populations that facilitate a rapid transition towards chitin degradation when required. For the first time, a model of chitin degradation by Serratia marcescens is proposed, and aspects that currently remain elusive are highlighted. Hence, this review provides the basis for further investigations to reach a holistic understanding of this intriguing and important biological system.