Identification of Novel Acinetobacter baumannii Type VI Secretion System Antibacterial Effector and Immunity Pairs

Abstract

The type VI secretion system (T6SS) is a macromolecular machine that delivers protein effectors into host cells and/or competing bacteria. The effectors may be delivered as noncovalently bound cargo of T6SS needle proteins (VgrG/Hcp/PAAR) or as C-terminal extensions of these proteins. Many strains produce a T6SS, but little is known about the specific effectors or how they are delivered. In this study, we show that AB307-0294 encodes three loci, each containing a gene, a T6SS toxic effector gene, and an antitoxin/immunity gene. Each of the T6SS toxic effectors could kill when produced in unless the cognate immunity protein was coproduced. To determine the role of each VgrG in effector delivery, we performed interbacterial competitive killing assays using AB307-0294 mutants, together with prey cells expressing pairs of immunity genes that protected against two toxic effectors but not a third. Using this approach, we showed that AB307-0294 produces only three T6SS toxic effectors capable of killing and that each VgrG protein is specific for the carriage of one effector. Finally, we analyzed a number of genomes and identified significant diversity in the range of encoded T6SS VgrG and effector proteins, with correlations between effector types and global clone lineages.

The Tip of the VgrG Spike Is Essential to Functional Type VI Secretion System Assembly in Acinetobacter baumannii

“…8), the DUF2345 domain may require additional elements present at the C terminus of VgrG for proper function. Moreover, a recent bioinformatic analysis of 73 VgrGs across 22 A. baumannii strains, as well as the soil bacterium A. baylyi ADP1, showed that all VgrGs contain a DUF2345 domain (58). The high levels of conservation suggest that the It is noteworthy that our results are not in conflict with previous results indicating that the C terminus of VgrG is dispensable for T6SS function (52,53).…”

“…Given that we identified no differences in the predicted functional domains of canonical VgrGs and those of VgrGi, we reasoned that VgrGi may possess critical differences in its primary sequence that are responsible for its inhibitory ability. VgrGs encoded by A. baumannii strains were recently grouped into six distinct phylogenetic groups (58). Based on the amino acid identity (Ͼ95%), we determined that VgrGi belongs to class 1 VgrGs.…”

Redundancy and Specificity of Type VI Secretion vgrG Loci in Antibacterial Activity of Agrobacterium tumefaciens 1D1609 Strain

“…brasiliense strain PBR 1692 (Bellieny-Rabelo et al, 2019) but no nuclease activity has been tested. In Acinetobacter baylyi, it was shown that the genomic DNA was completely degraded when Rhs2 with C-terminal AHH motif is expressed in E. coli (Fitzsimons et al, 2018). In this study, we characterize further to show that the AHH motif is indeed responsible for the DNase activity ( Figure 5).…”

Crucial Role of the Accessory Genome in the Evolutionary Trajectory of Acinetobacter baumannii Global Clone 1

“…Regarding virulence factors, A. baumannii usually encodes a type VI secretion system (T6SS), which can be used to kill competitors (Weber et al, 2013). It is likely that the presence of this system may be associated to the survival in the nosocomial niche (Fitzsimons et al, 2018). Here, we searched the genes coding for the proteins critical for T6SS operation (Weber et al, 2016;Repizo et al, 2019) in Groups 1, 2, 3 and 4, as well as tetR1 and tetR2 repressors in Groups 1, 2 and 3 ( Supplementary Table 13).…”