Conserved FimK truncation coincides with increased expression of type 3 fimbriae and cultured bladder epithelial cell association in Klebsiella quasipneumoniae
Klebsiella spp. commonly cause both uncomplicated urinary tract infection (UTI) and recurrent UTI (rUTI). Klebsiella quasipneumoniae, a relatively newly defined species of Klebsiella, has been shown to be metabolically distinct from Klebsiella pneumoniae, but its urovirulence mechanisms have not been defined. K. pneumoniae uses both type 1 and type 3 fimbriae to attach to host epithelial cells. The type 1 fimbrial operon is well-conserved between Escherichia coli and K. pneumoniae with the exception of fimK, which is unique to Klebsiella spp. FimK contains an N-terminal DNA binding domain and a C-terminal phosphodiesterase (PDE) domain that has been hypothesized to cross-regulate type 3 fimbriae expression via modulation of cellular levels of cyclic di-GMP. Here, we find that a conserved premature stop codon in K. quasipneumoniae fimK results in truncation of the C-terminal PDE domain and that the bladder epithelial cell association and invasion of uropathogenic K. quasipneumoniae strain KqPF9 is dependent on type 3 but not type 1 fimbriae. Further, we show that basal expression of both type 1 and type 3 fimbrial operons as well as bladder epithelial cell association is elevated in KqPF9 relative to uropathogenic K. pneumoniae TOP52 and that complementation of KqPF9{Delta}fimK with the TOP52 fimK allele reduced type 3 fimbrial expression and bladder epithelial cell attachment. Taken together these data suggest that the C-terminal PDE of FimK can modulate type 3 fimbrial expression in K. pneumoniae and its absence in K. quasipneumoniae may lead to a loss of type 3 fimbrial cross-regulation. ImportanceK. quasipneumoniae is often indicated as the cause of many opportunistic infections including urinary tract infection (UTI), which affects >50% of women worldwide. However, virulence mechanisms of K. quasipneumoniae remain uninvestigated. Prior to this work, K. quasipneumoniae and K. pneumoniae had only been distinguished phenotypically by metabolic differences. This work contributes to the understanding of K. quasipneumoniae virulence phenotypes by evaluating the contribution of type 1 and type 3 fimbriae, which are critical colonization factors encoded by all Klebsiella spp., to K. quasipneumoniae bladder epithelial cell attachment. We identify clear phenotypic differences in both bladder epithelial cell attachment between uropathogenic K. pneumoniae and K. quasipneumoniae. Importantly, we find that a structural difference in the fimbrial regulatory gene fimK may contribute to differential co-regulation of type 1 and type 3 fimbriae between the two Klebsiella species.