The bacterial predator Myxococcus xanthus uses two LcrH-like chaperones with unprecedented substrates to lyse prey cells

In soil environments, microorganisms constantly compete for limited nutrients. To secure their resources, selected bacterial species act as predators, i.e. they kill other bacteria to consume their biomass. An important model to study bacterial predation is Myxococcus xanthus, which uses a broad prey spectrum and possesses a distinct predation machinery. M. xanthus kills its prey in direct cell-cell contact using two protein secretion systems [1]. A Tad-like "Kil" system seems to mediate prey killing, and an atypical type 3 secretion system (T3SS*) is responsible for prey lysis [2]. Compared to other T3SS, the T3SS* in M. xanthus lacks a needle and other outer membrane components, yet it is fully functional.

To address the question of whether and how the T3SS* might secrete effector proteins across the M. xanthus cell envelope to the prey cell, we initially investigate the role of putative chaperones. These chaperones presumably bind specific substrates to recruit them for secretion. Phenotypic analysis showed that two out of four LcrH-like chaperones within the T3SS* gene cluster are required for T3SS*-dependent prey lysis. However, homologues to known T3SS effectors were not found in the M. xanthus genome. We are currently looking into candidate effectors for each chaperone by screening deletion mutants. First interactions between chaperone-effector pairs were identified using in vitro pulldown assays. To localize these T3SS* components upon prey contact, we perform fluorescence microscopy and aim to unravel their role within the predation machinery.

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This work is funded by Deutsche Forschungsgemeinschaft DFG.