Characterization of Two Novel Predatory Bacteria, Bacteriovorax stolpii HI3 and Myxococcus sp. MH1, Isolated from a Freshwater Pond: Prey Range, and Predatory Dynamics and Efficiency

Abstract

Predatory bacteria, which prey on other bacteria, have significant functions in microbial ecosystems and have attracted increasing attention for their biotechnological use. However, knowledge of the characteristics of wild-type environmental predatory bacteria remains limited. This study isolated two predatory bacteria, Bacteriovorax stolpii HI3 and Myxococcus sp. MH1, from a freshwater pond and characterized their predation capabilities. Determination of the prey range using 53 potential prey strains, including 52 environmental strains, revealed that B. stolpii HI3 and Myxococcus sp. MH1 could prey on a wide spectrum of Gram-negative bacteria and a broader range of bacteria, irrespective of phylogeny, in accordance with the common characteristics of Bdellovibrio and like organisms and myxobacteria, respectively. Liquid culture assays also found that although predation by B. stolpii HI3 rapidly and largely occurred, the prey bacteria regrew, possibly through plastic phenotypic resistance to predation. In contrast, predation by Myxococcus sp. MH1 occurred at relatively low efficiency but was longer lasting. The two strains exhibited slightly distinct temperature preferences but commonly preferred slightly alkaline pH. The novel findings of this study provide evidence for the coexistence of predatory bacteria with diverse predation capabilities in the natural aquatic environment.

Keywords: Bacteriovorax; Myxococcus; freshwater pond; isolation; predation dynamics; predatory bacteria; prey range.

Figure 1

Phylogenetic tree based on 16S rRNA gene sequences from isolated predatory strains HI3 (a) and MH1 (b) and the type strains of their related genera. Evolutionary relationship was inferred using neighbor-joining method, with Kimura 2-parameter model. Geobacter metallireducens GS-15^T was used as an outgroup. Accession numbers of nucleotide sequences for type strains are provided in parentheses. Bootstrap values >50% based on 1000 replicates are shown at nodes. Scale bar represents 0.05 (a) or 0.02 (b) nucleotide substitution per site.

Figure 2

Prey range specificities of Bacteriovorax stolpii HI3 and Myxococcus sp. MH1 on 53 potential prey strains. Detailed phylogenetic information of potential prey strains is provided in Table S1. +, predation; −, no predation.

Figure 3

Temporal changes in predator and prey cell densities and dissolved organic carbon (DOC) concentration, during co-cultivation of Bacteriovorax stolpii HI3 (a) or Myxococcus sp. MH1 (b) as predator, with Escherichia coli HB101 as prey. Error bars represent standard deviation (n = 3).

Figure 4

Effects of temperature (a) and pH (b) on Bacteriovorax stolpii HI3 predation on Escherichia coli HB101. Temporal variations of HB101 cell density were monitored. Error bars represent standard deviation (n = 3, except several data where n = 2).

Figure 5

Effects of temperature (a) and pH (b) on Myxococcus sp. MH1 predation on Escherichia coli HB101. Temporal variations of HB101 cell density were monitored. Error bars represent standard deviation (n = 3, except several data where n = 2).