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

Abstract

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 wcaJ on 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 w caJ , 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 w caJ could not. Discussion The interaction of multiple factors is involved in capsule synthesis, including w caJ and r mpA . 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, w caJ sequence consistency is limited to the same serotype, which cause wcaJ functioning in different serotype strains with sequence recognition specificity.