An MltA-Like Lytic Transglycosylase Secreted by Bdellovibrio bacteriovorus Cleaves the Prey Septum during Predatory Invasion.

Lytic transglycosylases cut peptidoglycan backbones, facilitating a variety of functions within bacteria, including cell division, pathogenesis, and insertion of macromolecular machinery into the cell envelope. Here, we identify a novel role of a secreted lytic transglycosylase associated with the predatory lifestyle of Bdellovibrio bacteriovorus strain HD100. During wild-type B. bacteriovorus prey invasion, the predator rounds up rod-shaped prey into spherical prey bdelloplasts, forming a spacious niche within which the predator grows. Deleting the MltA-like lytic transglycosylase Bd3285 still permitted predation but resulted in three different, invaded prey cell shapes: spheres, rods, and "dumbbells." Amino acid D321 within the catalytic C-terminal 3D domain of Bd3285 was essential for wild-type complementation. Microscopic analyses revealed that dumbbell-shaped bdelloplasts are derived from Escherichia coli prey undergoing cell division at the moment of Δ bd3285 predator invasion. Prelabeling of E. coli prey peptidoglycan prior to predation with the fluorescent D-amino acid HADA showed that the dumbbell bdelloplasts invaded by B. bacteriovorus Δ bd3285 contained a septum. Fluorescently tagged Bd3285, expressed in E. coli, localized to the septum of dividing cells. Our data indicate that B. bacteriovorus secretes the lytic transglycosylase Bd3285 into the E. coli periplasm during prey invasion to cleave the septum of dividing prey, facilitating prey cell occupation. IMPORTANCE Antimicrobial resistance is a serious and rapidly growing threat to global health. Bdellovibrio bacteriovorus can prey upon an extensive range of Gram-negative bacterial pathogens and thus has promising potential as a novel antibacterial therapeutic and is a source of antibacterial enzymes. Here, we elucidate the role of a unique secreted lytic transglycosylase from B. bacteriovorus which acts on the septal peptidoglycan of its prey. This improves our understanding of mechanisms that underpin bacterial predation.