Comparative genomics of obligate predatory bacteria belonging to phylum <i>Bdellovibrionota</i> highlights distribution and predicted functions of lineage-specific protein families

Comparative genomics of predatory bacteria is important to understand their ecology and evolution and explore their potential to treat drug-resistant infections. We compared chromosomes of 18 obligate predators from phylum <i>Bdellovibrionota</i> (16 intraperiplasmic, two epibiotic) and 15 non-predatory bacteria. Phylogenetics of conserved single-copy genes and analysis of genome-wide average amino acid identity provide evidence for at least five <i>Bdellovibrio</i> species and support recent reclassifications of predatory taxa. To define shared and differential genome content, we grouped predicted protein sequences into gene clusters based on sequence similarity. Few gene clusters are shared by all 33 bacteria or all 18 predatory bacteria; however, we identified gene clusters conserved within lineages, such as intraperiplasmic <i>Bdellovibrio</i>, and not found in other bacteria. Many of these are predicted to function in cell envelope biogenesis, signal transduction, and other roles important for predatory lifestyles. Among intraperiplasmic <i>Bdellovibrio</i>, we detected high abundance of gene clusters predicted to encode transglycosylases, endopeptidases, and lysozymes, and we identified six gene clusters (amidase, L,D-transpeptidase, four transglycosylases) with evidence of recent gene duplication and gene family expansion. Focusing on peptidoglycan metabolism, we defined a suite of gene clusters that include peptidoglycan-degrading and -modifying enzymes and occur only in predatory bacteria, suggesting these proteins may have evolved activities specific to predation. Our analyses highlight key genome content differences between obligate predatory bacteria and non-predatory relatives and identify gene clusters that may encode enzymes adapted to predatory lifestyles. These lineage-specific proteins are strong candidates for functional characterization to clarify their role in predation.IMPORTANCEEvolution of predation as a bacterial lifestyle involves selective pressure on and adaptation of enzymes that contribute to killing and digestion of prey bacteria, in some cases from within the prey itself. Such enzymes are a hallmark of obligate predatory bacteria belonging to phylum <i>Bdellovibrionota</i>, which includes the well-studied predator <i>Bdellovibrio</i>. By comparing protein sequences of obligate predatory bacteria and their non-predatory relatives, we define key genome content differences that distinguish bacterial predators and identify lineage-specific enzymes that may have evolved unique activities due to selective pressures related to a predatory lifestyle. In addition to providing insights into the ecology and evolution of predatory bacteria, comparative genomics studies, like this, can inform efforts to develop predatory bacteria and/or their enzymes as potential biocontrol agents to combat drug-resistant bacterial infections.