Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2018

Unlocking the Complete Arsenal of Acinetobacter baumannii Type VI Secretion System Effectors (#318)

Jessica M Lewis 1 , Timothy C Fitzsimons 1 , Deanna Deveson Lucas 1 , Marina Harper 1 , John D Boyce 1
  1. Department of Microbiology, Infection and Immunity Program, Monash Biomedicine Discovery Institute, Monash University, Clayton, VIC, Australia

Nearly 10% of all nosocomial Gram‑negative bacterial infections are caused by Acinetobacter baumannii, a strictly aerobic coccobacillus. A. baumannii expresses a type VI secretion system (T6SS), a unique surface structure resembling an inverted T4 bacteriophage that is used by A. baumannii to inject effectors into nearby cells. In some bacteria, the T6SS is used to inject effectors involved in virulence or biofilm formation, but in A. baumannii the T6SS is primarily associated with killing competitor bacteria. In A. baumannii strains ATCC17978 and AB307‑0294, the secretion of each toxic effector is dependent upon a specific VgrG protein. The genes encoding the effector and its cognate VgrG protein are often co‑localised on the chromosome. In order to identify novel A. baumannii effectors, we analysed the genomes of 41 strains representing a range of A. baumannii global clone lineages and sequence types. Several putative effector genes were identified in each genome, each of which were adjacent to a gene encoding a protein with a VgrG-domain. In total, 29 putative A. baumannii T6SS effector genes were identified and grouped based on shared domains and the level of amino acid identity. The effectors identified included six Rhs‑domain family proteins, each with a unique C‑terminal domain of no known function, eight predicted peptidoglycan hydrolases, and three putative nucleases. Moreover, several putative effectors contained a predicted lipase motif. Eight of the putative effectors were novel and had no identifiable domains. Our aim is to characterise the novel effectors via heterologous expression in E. coli and in vitro functional assays. Characterisation of these novel effectors will provide an insight into bacterial killing mechanisms and potentially allow for the identification of new drug targets.