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

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, HI3 and 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 HI3 and 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 and like organisms and myxobacteria, respectively. Liquid culture assays also found that although predation by HI3 rapidly and largely occurred, the prey bacteria regrew, possibly through plastic phenotypic resistance to predation. In contrast, predation by 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.