Regulation of Klebsiella pneumoniae mucoidy by the bacterial tyrosine kinase Wzc

Abstract

Klebsiella pneumoniae is a frequent nosocomial pathogen associated with urinary tract infections (UTI), pneumonia, and septicemia. Two lineages of K. pneumoniae have emerged that challenge the treatment of these infections. One lineage includes hypervirulent strains, causing invasive community-acquired infections, and the other encompasses carbapenem-resistant isolates. Non-mucoid, carbapenem-resistant isolates are most frequently isolated from UTI. Therefore, we hypothesized that environmental conditions may drive K. pneumoniae adaptation to the urinary tract. We found that two rmp-positive, hypervirulent strains and two rmp-negative clinical UTI isolates all suppressed mucoidy when cultured in urine compared to rich LB medium without altering capsular polysaccharide (CPS) abundance. We then performed a transposon screen to identify genetic factors through which urine suppresses mucoidy. Due to variations within transposon hits, we performed whole genome sequencing on our hits and found 100% association between secondary mutations in Wzc and increased mucoidy. Wzc is an inner membrane tyrosine kinase that regulates CPS assembly. When Wzc mutations are encoded chromosomally we observed both increased mucoidy and increased cell-free extracellular polysaccharide (EPS). However, when Wzc mutations are expressed in trans we observed increased mucoidy without impacting CPS or cell-free EPS abundance. Functionally, one periplasmic mutation increased Wzc autophosphorylation, while four active site mutations reduced Wzc autophosphorylation. These four active site mutations are also sufficient to increase mucoidy in one of the rmp-negative clinical UTI isolates without affecting EPS abundance. Combined, these data implicate mutation-driven modulation of Wzc activity as a global, rmp-independent mechanism for increasing K. pneumoniae mucoidy, without altering EPS uronic acid content. Wzc activity may represent the lynchpin that coordinates both capsule biosynthesis and mucoidy, explaining why these two phenotypes have been historically intertwined.