| Acinetobacter nosocomialis is a member of the Acinetobacter calcoaceticus-baumannii complex, which are Gram-negative opportunistic pathogens of increasing relevance worldwide. Medically relevant Acinetobacter species form biofilms, are resistant to desiccation, and easily acquire antibiotic resistance genes, all of which contribute to its ability to cause disease. Despite many reports on the epidemiology and antibiotic resistance phenotypes of Acinetobacter, there are limited reports characterizing the virulence mechanisms of these important nosocomial pathogens. Type IV pili (Tfp) are transenvelope protein complexes that can act as surface appendages mediating many bacterial processes. Analysis of the genomes of fully sequenced medically relevant Acinetobacter strains reveals the presence of genes that encode proteins predicted to be involved with the biogenesis of Tfp. Furthermore, many medically relevant Acinetobacter species have been shown to exhibit twitching motility and natural transformation, two classical Tfp-associated phenotypes. Therefore we utilized mutagenesis strategies to selectively delete genes encoding proteins predicted to be involved in Tfp biogenesis and probed for Tfp functionality. In our analysis we determined that A. nosocomialis strain M2 did produce functional Tfp, which were required for natural transformation and twitching motility. During the course of our studies we also identified that the major pilin subunit, PilA, of the Tfp fiber was post-translationally modified. Subsequently we determined that PilA was glycosylated by the pilin-specific oligosaccharyltransferase, TfpO, at the carboxy-terminal serine. Lastly, we demonstrated that many Acinetobacter species encode two functional oligosaccharyltransferases, one devoted exclusively to pilin glycosylation and the other to general protein glycosylation. This study is the first to describe the production of functional Tfp production by a medically relevant Acinetobacter species and also demonstrated that the pilin glycosylation system shares a common pathway with the general protein glycosylation pathway. |
