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

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. [Display omitted] • Cell contact-dependent prey killing involves two distinct protein secretion systems • Combined action of Tad- and type 3-like systems induces prey cell death and lysis • Components of both systems interdependently accumulate at the predator-prey interface • Respective M. xanthus mutants are impaired in powering motility with prey biomass Bacterial predation is abundant in different habitats, but mechanistic insight is lacking. Thiery et al. determine distinct functions of two atypical protein secretion systems in predatory Myxobacteria: a Tad-like complex and a rudimentary, needle-less type 3-like system act together to induce cell death and lysis of bacterial cells. [ABSTRACT FROM AUTHOR]