Regulation of the chitin degradation and utilization system by the ChiX small RNA in Serratia marcescens 2170

Serratia marcescens 2170 produces three different types of chitinases and chitin-binding protein CBP21. We found that transposon insertion into the 5′ untranslated region (5′ UTR) of chiPQ-ctb led to defective chitinase and CBP21 production. ChiX small RNA possessed the complementary sequence of the 5′ UTRs of the chiPQ-ctb and chiR and repressed the expression of chiP and chiR. ChiX was detected in a medium containing glucose, glycerol, GlcNAc, and (GlcNAc)2, but the expression of both chiP and chiR was only observed in a medium containing (GlcNAc)2. ∆chiX mutant produced chitinases, CBP21, and chitobiase without induction. chiP transcripts were more abundant than those of chiR or chiX in a medium containing (GlcNAc)2. These results suggest that the constitutively expressed ChiX binds to the highly abundant chiP 5′ UTR, thereby leading to the induction of chiR mRNA translation and the subsequent expression of chitinases and CBP21.