Identification of the first two virulence genes of Moraxella osloensis in the slug Deroceras reticulatum

Abstract

The bacterium Moraxella osloensis associated with the nematode Phasmarhabditis hermaphrodita is a pathogen of slug Deroceras reticulatum. Nematode infective juveniles vector M. osloensis into the shell cavity of D. reticulatum, and the slug is killed within 4-16 days. Gene expression profile of M. osloensis in the slug was analyzed and differentially expressed genes were identified using a selective capture of transcribed sequences (SCOTS) technique. Most identified sequences were homologous to other bacteria, and function as putative cell structure, energy metabolism, degradation, translocation, and unknown function proteins. Other identified sequences did not exhibit similarity to any genes or gene products in current databases, and are thus novel. We further evaluated the role of SCOTS identified two genes, M5 (protein-disulfide isomerase) and M8 (protein kinase), in the virulence of M. osloensis to the slug using mutation and complementation strategy. Mutants were constructed with insertion-deletion strategy by inverse PCR. The full length of M5 and M8 fragments were obtained by inverse PCR to complement mutants. Compared to the wild type, the virulence of M. osloensiss mutants to the slug was markedly reduced and could be complemented. Therefore, we conclude that the in vivo expressed genes, M5 and M8, contribute to M. osloensis virulence to the slug. This study provided a first glimpse to the gene expression in a mollusk host during bacterial infection, and insights into understanding the mechanism of the bacterial virulence to a mollusk host.