Regulation of the chitin degradation and utilization system by the ChiX small RNA in <i>Serratia marcescens</i> 2170
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<i>Serratia marcescens</i> 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 <i>chiPQ</i>-<i>ctb</i> led to defective chitinase and CBP21 production. ChiX small RNA possessed the complementary sequence of the 5′ UTRs of the <i>chiPQ</i>-<i>ctb</i> and <i>chiR</i> and repressed the expression of <i>chiP</i> and <i>chiR</i>. ChiX was detected in a medium containing glucose, glycerol, GlcNAc, and (GlcNAc)<sub>2</sub>, but the expression of both <i>chiP</i> and <i>chiR</i> was only observed in a medium containing (GlcNAc)<sub>2</sub>. ∆<i>chiX</i> mutant produced chitinases, CBP21, and chitobiase without induction. <i>chiP</i> transcripts were more abundant than those of <i>chiR</i> or <i>chiX</i> in a medium containing (GlcNAc)<sub>2</sub>. These results suggest that the constitutively expressed ChiX binds to the highly abundant <i>chiP</i> 5′ UTR, thereby leading to the induction of <i>chiR</i> mRNA translation and the subsequent expression of chitinases and CBP21.
