The importance of chitobiase and N-acetylglucosamine (GlcNAc) uptake in N,N′-diacetylchitobiose [(GlcNAc)2] utilization by Serratia marcescens 2170

摘要

N,N′-diacetylchitobiose [(GlcNAc)2] is the main degradation product from chitin by the action of chitinases of Serratia marcescens 2170. Uptake of (GlcNAc)2 via a (GlcNAc)2-specific enzyme II permease by this bacterium has been demonstrated previously. Here, we report the contribution of chitobiase and N-acetylglucosamine (GlcNAc) uptake to the utilization of (GlcNAc)2. When S. marcescens 2170 was cultivated in a medium containing chitin, chitobiase activity was detected both inside and outside the cells; intracellular chitobiase was more abundant and suggested to be mainly located in the periplasm. Production of chitobiase was induced by GlcNAc and more effectively by (GlcNAc)2. For induction of chitobiase, uptake of (GlcNAc)2 was essential but ChiR, an essential regulator of chitinase induction, was not required. S. marcescens 2170 grew well on both GlcNAc and (GlcNAc)2 but mutants defective in either chitobiase or NagE, the GlcNAc-specific enzyme II permease, showed reduced growth on (GlcNAc)2. These results suggest that, in addition to uptake as (GlcNAc)2, a proportion of the (GlcNAc)2 is converted to GlcNAc by chitobiase, mainly in the periplasm, and incorporated into the cytoplasm by NagE. The mutant defective in chitobiase grew more slowly on (GlcNAc)2 than on GlcNAc, indicating that (GlcNAc)2 is less efficiently fermented by S. marcescens 2170 in the absence of chitobiase. Therefore, uptake as both (GlcNAc)2 and GlcNAc is important for efficient utilization of (GlcNAc)2 in S. marcescens.