Ecological variables affecting predatory success in Myxococcus xanthus.

The feeding efficiency of microbial predators depends on both the availability of various prey species and abiotic variables. Myxococcus xanthus is a bacterial predator that searches for microbial prey by gliding motility, and then kills and lyses its prey with secreted compounds. We manipulated three ecological variables to examine their effects on the predatory performance of M. xanthus to better understand its behavior and how it affects prey populations. Experiments were designed to determine how surface solidity (hard vs soft agar), density of prey patches (1 vs 2 cm grids), and type of prey (Gram-positive Micrococcus luteus vs Gram-negative Escherichia coli) affect predatory swarming and prey killing by M. xanthus. The prey were dispersed in patches on a buffered agar surface. M. xanthus swarms attacked a greater proportion of prey patches when patches were densely arranged on a hard-agar surface, compared with either soft-agar surfaces or low-patch-density arrangements. These ecological variables did not significantly influence the rate of killing of individual prey within a patch, although a few surviving prey were more likely to be recovered on soft agar than on hard agar. These results indicate that M. xanthus quickly kills most nearby E. coli or M. luteus regardless of the surface. However, the ability of M. xanthus to search out patches of these prey is affected by surface hardness, the density of prey patches, and the prey species.