Different regulatory mechanisms of the capsule in hypervirulent Klebsiella pneumonia: “direct” wcaJ variation vs. “indirect” rmpA regulation

INTRODUCTION: Hypervirulent Klebsiella pneumoniae produce an increased amount of capsular substance and are associated with a hypermucoviscous phenotype. Capsule production is regulated by capsular regulatory genes and capsular gene cluster variations. In the present study, we focus on the effect of rmpA and wcaJon capsule biosynthesis. METHODS: Phylogenetic trees were constructed to analyze wcaJ and rmpA sequence diversity in different serotypes hypervirulent strains. Then mutant strains (K2044(ΔwcaJ), K2044(K1wcaJ), K2044(K2wcaJ)and K2044(K64wcaJ)) were used to verify the effects of wcaJ and its diversity on capsule synthesis and strain virulence. Furthmore, the role of rmpA in capsular synthesis and its mechanisms were detected in K2044(ΔrmpA) strain. RESULTS: RmpA sequences are conversed in different serotypes. And rmpA promoted the production of hypercapsules by simultaneously acting on three promoters in cps cluster. Whereas wcaJ, its sequences are different in different serotypes, and its loss result in the termination of capsular synthesis. Moreover, the results verified that K2 wcaJ could form hypercapsule in K2044 strains (K1 serotype), but K64 wcaJ could not. DISCUSSION: The interaction of multiple factors is involved in capsule synthesis, including wcaJ and rmpA. RmpA, an known conserved capsular regulator gene, acts on cps cluster promoters to promote the production of the hypercapsule. WcaJ as initiating enzyme of CPS biosynthesis, its presence determines the synthesis of capsule. Besides, different from rmpA, wcaJ sequence consistency is limited to the same serotype, which cause wcaJ functioning in different serotype strains with sequence recognition specificity.