Variation in genome content and predatory phenotypes betweenBdellovibriosp. NC01 isolated from soil andB. bacteriovorustype strain HD100

Abstract

13Defining phenotypic and associated genotypic variation among Bdellovibrio may further 14 our understanding of how this genus attacks and kills different Gram-negative bacteria. We 15 isolated Bdellovibrio sp. NC01 from soil. Analysis of 16S rRNA gene sequences and average 16 amino acid identity showed that NC01 belongs to a different species than the type species 17 bacteriovorus. By clustering amino acid sequences from completely sequenced Bdellovibrio and 18 comparing the resulting ortholog groups to a previously published analysis, we defined a "core 19 genome" of 778 protein-coding genes and identified four protein-coding genes that appeared to 20 be missing only in NC01. To determine how horizontal gene transfer (HGT) may have impacted 21 NC01 genome evolution, we performed genome-wide comparisons of Bdellovibrio nucleotide 22 sequences, which indicated that eight NC01 genomic regions were likely acquired by HGT. To 23 investigate how genome variation may impact predation, we compared protein-coding gene 24 content between NC01 and the B. bacteriovorus type strain HD100, focusing on genes 25 implicated as important in successful killing of prey. Of these, NC01 is missing ten genes that 26 may play roles in lytic activity during predation. Compared to HD100, NC01 kills fewer tested 27 prey strains and kills E. coli ML35 less efficiently. NC01 causes a smaller log reduction in 28 ML35, after which the prey population recovers and the NC01 population decreases. In addition, 29 NC01 forms turbid plaques on lawns of E. coli ML35, in contrast to clear plaques formed by 30 HD100. Linking phenotypic variation in interactions between Bdellovibrio and Gram-negative 31 bacteria with underlying Bdellovibrio genome variation is valuable for understanding the 32 ecological significance of predatory bacteria and evaluating their effectiveness in clinical 33 applications.34 35Since their discovery in the early 1960s, predatory bacteria have been isolated from a 36 wide range of terrestrial and aquatic environments, including some with extreme conditions such 37 as high temperature or salinity (1). The impact of predatory bacteria in these environments is not 38 fully known, but recent studies indicate they may play an important role in shaping microbial 39 communities (2-4). In addition, their ability to attack and kill Gram-negative bacterial pathogens 40 has generated interest in developing predatory bacteria as biocontrol agents to combat drug-41 resistant infections (5-7). Given their potential ecological significance and possible clinical 42 applications, it is important to define phenotypic and genotypic variation among predatory 43 bacteria. In particular, variation in predatory phenotypes such as prey range and predation 44 efficiency will affect how different strains of predatory bacteria impact microbial communities, 45 and this phenotypic variation may be determined by variation in genome content. To further our 46 understanding of phenotypic and genome variation in predatory bacteria, we isolated, assayed 4...