Novel Genes Required for Surface-Associated Motility in Acinetobacter baumannii

Abstract

Acinetobacter baumannii is an opportunistic and increasingly multi-drug resistant human pathogen rated as a critical priority one pathogen for the development of new antibiotics by the WHO in 2017. Despite the lack of flagella, A. baumannii can move along wet surfaces in two different ways: via twitching motility and surface-associated motility. While twitching motility is known to depend on type IV pili, the mechanism of surface-associated motility is poorly understood. In this study, we established a library of 30 A. baumannii ATCC® 17978™ mutants that displayed deficiency in surface-associated motility. By making use of natural competence, we also introduced these mutations into strain 29D2 to differentiate strain-specific versus species-specific effects of mutations. Mutated genes were associated with purine/pyrimidine/folate biosynthesis (e.g. purH, purF, purM, purE), alarmone/stress metabolism (e.g. Ap4A hydrolase), RNA modification/regulation (e.g. methionyl-tRNA synthetase), outer membrane proteins (e.g. ompA), and genes involved in natural competence (comEC). All tested mutants originally identified as motility-deficient in strain ATCC® 17978™ also displayed a motility-deficient phenotype in 29D2. By contrast, further comparative characterization of the mutant sets of both strains regarding pellicle biofilm formation, antibiotic resistance, and virulence in the Galleria mellonella infection model revealed numerous strain-specific mutant phenotypes. Our studies highlight the need for comparative analyses to characterize gene functions in A. baumannii and for further studies on the mechanisms underlying surface-associated motility.

Global regulator DksA modulates virulence of Acinetobacter baumannii

“…These results suggest that (p)ppGpp and DksA play an opposite role in the surface motility of A. baumannii . Genetic analysis of A. baumannii identified 30 genes that were associated with surface motility, including genes encoding the 1,3-diaminopropane biosynthesis, alarmone/stress metabolism, DNA modification/repair/uptake, lipopeptide synthesis/export, outer membrane proteins, oxidative stress, purine/pyrimidine/folate biosynthesis, RNA modification/regulation, and others [ 49 ]. Of the genes associated with surface motility, ompA was downregulated in the ∆ dksA mutants.…”

Deciphering the virulence factors, regulation, and immune response to Acinetobacter baumannii infection

“…In a Galleria mellonella infection model, surface-associated motility which is an appendageindependent form of movement, was found to play a more important role in virulence than twitching motility (Corral et al, 2021). Surface-associated motility is probably driven by the extrusion of extracellular polymeric substances and is associated with the synthesis of 1,3-diaminopropane (Skiebe et al, 2012), lipooligosaccharide production (McQueary et al, 2012), outer membrane and natural competence proteins (Blaschke et al, 2021), and proteins associated with superfamilies of efflux pumps (Peŕez-Varela et al, 2019). The regulators of surface-associated motility include cyclic diguanylate (Ahmad et al, 2020), quorum sensing (Clemmer et al, 2011), CheW/Che Aanalogs (Corral et al, 2020), and EnvZ/OmpR -two component system (Tipton and Rather, 2017).…”

Csu pili dependent biofilm formation and virulence of Acinetobacter baumannii

“…The mechanisms behind this form of mobility are very poorly understood 20 . Multiple regulators, such as purine and pyrimidine biosynthetic machineries, quorum sensing, natural competence, and c-di-GMP signalling, are known to be involved in surface associated motility 52 . The results of our phenotypic assays demonstrated very clearly that Csu pili and type IV pili inversely regulate the surface-associated motility of A. baumannii.…”