The predatory soil bacterium Myxococcus xanthus combines a Tad- and an atypical type 3-like protein secretion system to kill bacterial cells.

Abstract

Predatory Myxobacteria employ a multilayered predation strategy to kill and lyse soil microorganisms. Aiming to dissect the mechanism of contact-dependent killing of bacteria, we analyze four protein secretion systems in Myxococcus xanthus and investigate the predation of mutant strains on different timescales. We find that a Tad-like and a type 3-like secretion system (Tad and T3SS∗) fulfill distinct functions during contact-dependent prey killing: the Tad-like system is necessary to induce prey cell death, while the needle-less T3SS∗ initiates prey lysis. Fluorescence microscopy reveals that components of both systems interdependently localize to the predator-prey contact site prior to killing. Swarm expansion assays show that both Tad and T3SS∗ are required to handle live prey and that nutrient extraction from prey bacteria is sufficient to power M.xanthus motility. In conclusion, our observations indicate the functional interplay of two types of secretion systems for killing and lysis of bacterial cells.