Genetic analysis of surface motility in Acinetobacter baumannii

Abstract

The Gram-negative pathogen Acinetobacter baumannii strain M2 was found to exhibit a robust surface motility on low-percentage (0.2-0.4 %) agar plates. These patterns of motility were dramatically different depending on whether Difco or Eiken agar was used. Motility was observed in many, but not all, clinical and environmental isolates. The use of drop collapse assays to demonstrate surfactant production was unsuccessful, and the role of surfactants in A. baumannii M2 motility remains unclear. Surface motility was impaired by an insertion in pilT, encoding a gene product that is often required for retraction of the type IV pilus. Motility was also dependent on quorum sensing, as a null allele in the abaI autoinducer synthase decreased motility, and the addition of exogenous N-(3-hydroxy)-dodecanoylhomoserine lactone (3-OH C 12 -HSL) restored motility to the abaI mutant. Transposon mutagenesis was used to identify additional genes required for motility and revealed loci encoding various functions: non-ribosomal synthesis of a putative lipopeptide, a sensor kinase (BfmS), a lytic transglycosylase, O-antigen biosynthesis (RmlB), an outer membrane porin (OmpA) and de novo purine biosynthesis (PurK). Two of the above genes required for motility were highly activated by quorum sensing, and may explain, in part, the requirement for quorum sensing in motility.

DNA Uptake by the Nosocomial Pathogen Acinetobacter baumannii Occurs during Movement along Wet Surfaces

“…Even though phenotypically distinct, all forms of motility described for A. baumannii have been shown to depend on synthesis of the polyamine 1,3-diaminopropane (26). Surface motility of A. baumannii was further shown to be controlled by blue light sensing (28) and quorum sensing (24,29) and to depend on iron availability (30,31).…”

“…Only very recently was Acinetobacter motility further elucidated, providing evidence that at least in part it is driven by means of T4P in A. baumannii (22)(23)(24)(25)(26). Specifically, inactivation of pilT, putatively encoding an ATPase responsible for T4P retraction, reduced surface motility by roughly 50% (24). Residual activity observed with this pilT mutant could be due to the pilT paralogue pilU, known to be present in many representatives of A. baumannii (23).…”

“…Since that time, twitching motility has been intensively studied in many genera, including Myxococcus, Neisseria, Pseudomonas, and Haemophilus, firmly establishing that this form of movement is powered by depolymerization of type 4 pili (T4P) (18)(19)(20)(21). Only very recently was Acinetobacter motility further elucidated, providing evidence that at least in part it is driven by means of T4P in A. baumannii (22)(23)(24)(25)(26). Specifically, inactivation of pilT, putatively encoding an ATPase responsible for T4P retraction, reduced surface motility by roughly 50% (24).…”

“…Although an apparently complete set of genes required for natural transformation competence seems to be present in A. baumannii (23,25,37), to date, only a single isolate has been described to be naturally competent (13). Given the potential role of T4P in surface-associated motility of A. baumannii (17,(23)(24)(25)(26) and their established contribution to DNA uptake in various species (12,19,35), we speculated that A. baumannii might develop competence for DNA uptake while moving along wet surfaces in a T4P-dependent manner.…”

An ompR-envZ Two-Component System Ortholog Regulates Phase Variation, Osmotic Tolerance, Motility, and Virulence in Acinetobacter baumannii Strain AB5075

“…In E. coli, OmpR is known to regulate expression of flagellar biosynthesis and motility (23). Although A. baumannii does not encode flagella, motility in this organism has been characterized (24)(25)(26)(27)(28). Furthermore, the opaque and translucent variants of A. baumannii strain AB5075 exhibit significant differences with regard to surface motility on soft agar plates (10).…”