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.