Comparative analysis of myxococcus predation on soil bacteria

Abstract

Predator-prey relationships among prokaryotes have received little attention but are likely to be important determinants of the composition, structure, and dynamics of microbial communities. Many species of the soil-dwelling myxobacteria are predators of other microbes, but their predation range is poorly characterized. To better understand the predatory capabilities of myxobacteria in nature, we analyzed the predation performance of numerous Myxococcus isolates across 12 diverse species of bacteria. All predator isolates could utilize most potential prey species to effectively fuel colony expansion, although one species hindered predator swarming relative to a control treatment with no growth substrate. Predator strains varied significantly in their relative performance across prey types, but most variation in predatory performance was determined by prey type, with Gram-negative prey species supporting more Myxococcus growth than Gram-positive species. There was evidence for specialized predator performance in some predator-prey combinations. Such specialization may reduce resource competition among sympatric strains in natural habitats. The broad prey range of the Myxococcus genus coupled with its ubiquity in the soil suggests that myxobacteria are likely to have very important ecological and evolutionary effects on many species of soil prokaryotes.

FIG. 1.

(A) Mean predator swarm expansion on each prey type and on TPM, CTT, and TPM/CTT controls. Prey abbreviations: AG, Arthrobacter globiformis; CC, Curtobacterium citreum; BB, Bacillus bataviensis; CJ, Cytophaga johnsonae; ML, Micrococcus luteus; RV, Rhizobium vitis; SF, Sinorhizobium fredii; CT, Comamonas testosteroni; SY, Sphingobium yanoikuyae; EC, Escherichia coli; PF, Pseudomonas fluorescens; XF, Xanthomonas fragariae. Error bars represent ±1 standard error (SE) of the mean (n = 20 Myxococcus strains). (B) Mean swarm expansion of each Myxococcus strain across all prey species. Error bars represent ±1 SE of the mean (n = 12 prey species).

FIG. 2.

Variance in predatory swarm expansion of each Myxococcus strain across all prey species. Error bars represent ±1 SE of the mean (n = 5 replicates).

FIG. 3.

Grid of standardized predatory performance and neighbor-joining trees of predators and prey based on predation phenotypes. Red indicates faster swarming than average by a Myxococcus strain on the respective prey type, whereas blue indicates slower swarming than average, with color intensity reflecting the degree of difference from the mean. See the main text for further explanation of the figure.

FIG. 4.

Neighbor-joining tree of relationships among Myxococcus strains based on the clpX-icd-sglK MLST concatemer. Bootstrap support (1,000 replicates) is shown for each node. The scale bar reflects genetic distance as amino acid substitutions per site.