AUTHOR=Wang Weiwen , Tian Dongxing , Hu Dakang , Chen Wenjie , Zhou Ying , Jiang Xiaofei 

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

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1108818

DOI=10.3389/fcimb.2023.1108818

ISSN=2235-2988

ABSTRACT=<sec><title>Introduction</title><p>Hypervirulent <italic>Klebsiella pneumoniae</italic> 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 <italic>rmpA</italic> and <italic>wcaJ</italic>on capsule biosynthesis.</p></sec><sec><title>Methods</title><p>Phylogenetic trees were constructed to analyze wcaJ and rmpA sequence diversity in different serotypes hypervirulent strains. Then mutant strains (K2044<sup>ΔwcaJ</sup>, K2044<sup>K1wcaJ</sup>, K2044<sup>K2wcaJ</sup>and K2044<sup>K64wcaJ</sup>) 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<sup>ΔrmpA</sup> strain.</p></sec><sec><title>Results</title><p>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<italic>caJ</italic>, its sequences are different in different serotypes, and its loss result in the termination of capsular synthesis. Moreover, the results verified that K2 <italic>wcaJ</italic> could form hypercapsule in K2044 strains (K1 serotype), but K64 w<italic>caJ</italic> could not.</p></sec><sec><title>Discussion</title><p>The interaction of multiple factors is involved in capsule synthesis, including w<italic>caJ</italic> and r<italic>mpA</italic>. 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<italic>caJ</italic> sequence consistency is limited to the same serotype, which cause wcaJ functioning in different serotype strains with sequence recognition specificity.</p></sec>