Predatory activity of Myxococcus xanthus outer-membrane vesicles and properties of their hydrolase cargo

Abstract

The deltaproteobacterium Myxococcus xanthus predates upon members of the soil microbial community by secreting digestive factors and lysing prey cells. Like other Gram-negative bacteria, M. xanthus produces outer membrane vesicles (OMVs), and we show here that M. xanthus OMVs are able to kill Escherichia coli cells. The OMVs of M. xanthus were found to contain active proteases, phosphatases, other hydrolases and secondary metabolites. Alkaline phosphatase activity was found to be almost exclusively associated with OMVs, implying that there is active targeting of phosphatases into OMVs, while other OMV components appear to be packaged passively. The kinetic properties of OMV alkaline phosphatase suggest that there may have been evolutionary adaptation of OMV enzymes to a relatively indiscriminate mode of action, consistent with a role in predation. In addition, the observed regulation of production, and fragility of OMV activity, may protect OMV-producing cells from exploitation by M. xanthus cheating genotypes and/or other competitors. Killing of E. coli by M. xanthus OMVs was enhanced by the addition of a fusogenic enzyme (glyceraldehyde-3-phosphate dehydrogenase; GAPDH), which triggers fusion of vesicles with target membranes within eukaryotic cells. This suggests that the mechanism of prey killing involves OMV fusion with the E. coli outer membrane. M. xanthus secretes GAPDH, which could potentially modulate the fusion of co-secreted OMVs with prey organisms in nature, enhancing their predatory activity.

Myxobacteria Produce Outer Membrane-Enclosed Tubes in Unstructured Environments

“…When found as chains, the OMTs varied in length from 1 to Ͼ75 links. What appeared to be individual links in these images had a structure that was similar to OM vesicles produced by M. xanthus (23,24). Consequently we cannot distinguish between OM vesicles and single OMT links and whether they are different.…”

“…To test for the presence of SS OM -mCherry in slime trails, an A-motile strain (DW1053) was first incubated overnight without shaking and then spotted on thin pads (0.3 ml of 0.9% agarose in 1/4ϫ CTT) that had been prepared on glass slides. The resulting slides were incubated in a humid chamber at 33°C, and the cells were microscopically examined at 4,8,24, and 48 h for fluorescent trails.…”

The predatory life cycle of Myxococcus xanthus

“…Keane and J. Berleman between cells Palsdottir et al, 2009). OMVs contain a complex mixture of secondary metabolites, hydrolytic enzymes, chaperones and proteins of unknown function; OMV fractions purified from cells retain some lytic activity (Evans et al, 2012. Included in this is the protease MepA, which is responsible for most extracellular protease activity in Myx.…”

Identification of Functions Affecting Predator-Prey Interactions between Myxococcus xanthus and Bacillus subtilis

“…Other specialized metabolites found in membrane vesicles or secreted by M. xanthus comprise part of the predation machinery. Predation by M. xanthus is, therefore, multifactorial and complex in its overall regulation (24)(25)(26). Consistent with this perspective, genome analysis indicates that M. xanthus employs 18 polyketide synthase (PKS)/ nonribosomal peptide synthetase (NRPS) clusters (8.6% of the genome) to produce a large suite of specialized metabolites, some of which likely affect predation (27)(28)(29).…”