Variation in genome context and predatory phenotypes between Bdellovibrio sp. NC01 isolated from soil and B. bacteriovorus type strain HD100

Abstract

The range of naturally occurring variation in the ability of Bdellovibrio strains to attack and kill Gram-negative bacteria is not well understood. Defining phenotypic and associated genotypic variation among Bdellovibrio will clarify how divergent lineages within this genus impact microbial communities and will inform development of predatory bacteria as biocontrol agents to combat bacterial infections. We isolated Bdellovibrio sp. NC01 from soil and compared its genome and predatory phenotypes to B. bacteriovorus type strain HD100. Based on analysis of 16S rRNA gene sequences and average amino acid identity, NC01 belongs to a different species than HD100. Genome-wide comparisons and individual gene analyses indicated that eight NC01 genome regions were likely acquired by horizontal gene transfer (HGT), further supporting an important role for HGT in Bdellovibrio genome evolution. Within these regions, multiple protein-coding sequences were assigned predicted functions related to transcriptional regulation and transport; however, most were annotated as hypothetical proteins. Compared to HD100, NC01 has a limited prey range and kills E. coli ML35 less efficiently. Whereas HD100 drastically reduces the ML35 population and then maintains low prey population density, NC01 causes a smaller reduction in ML35, after which the prey population recovers, accompanied by a decrease in NC01. In addition, NC01 forms turbid plaques on lawns of ML35, in contrast to clear plaques formed by HD100. Characterizing variation in interactions between Bdellovibrio and Gram-negative bacteria, such as observed with NC01 and HD100, is important for understanding the ecological significance of predatory bacteria and evaluating their effectiveness in clinical applications. ImportanceBdellovibrio attack and kill Gram-negative bacteria; however, not all Bdellovibrio strains are equally efficient at killing the same Gram-negative bacteria. Defining how Bdellovibrio vary in predatory phenotypes and how this phenotypic variation relates to differences in genotype is important for understanding the ecological significance of predatory bacteria and evaluating their effectiveness in biocontrol of bacterial infections. We determined variation in genome content and predatory phenotypes, including prey range and predation efficiency, between Bdellovibrio sp. NC01 isolated from soil and B. bacteriovorus type strain HD100. NC01 is phylogenetically divergent from HD100, with eight regions of unique gene content likely acquired by horizontal gene transfer. Compared to HD100, the prey range of NC01 is limited, and it was less efficient at killing a strain of E. coli. These differences may have important implications for how each strain impacts microbial communities in different environments and for the effectiveness of each in clinical applications.