Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Microbiology and Immunology


Dr. Susan Koval


Bdellovibrio and like organisms (BALOs) are obligate predators of Gram negative bacteria. Predation occurs via a periplasmic or epibiotic life cycle. A periplasmic predator invades the periplasmic space of a prey while an epibiotic predator remains on the exterior.

An analysis of the genome sequences of periplasmic predators, Bdellovibrio bacteriovorus and Bacteriovorax marinus, and epibiotic predators, Bdellovibrio exovorus and Micavibrio aeruginosavorus determined that the genome size of epibiotic predators was smaller, while the metabolic networks were highly conserved. No core set of invasion-specific genes was identified.

Both life cycles were characterized by cryoelectron microscopy. The periplasmic predator, Bd. bacteriovorus, increased the volume of the periplasmic space prior to invasion. This coincided with a reduction in the size of the protoplast. A plug-like structure was found on the outer surface of bdelloplasts. Cryoelectron tomography suggested the plug originated from the flagellar end of the predator. It appears that upon invasion, Bd. bacteriovorus sheds the flagellum, which helps to seal the entry pore.

Analysis of PilT1 and PilT2 mutants of Bd. bacteriovorus showed that retraction of type IV pili was not required for invasion into the periplasmic space of the prey. However, a pilT2 mutant was unable to prey on a biofilm, suggesting that retraction of the pili may be required to penetrate the exopolysaccharide matrix layer.

Stenotrophomonas maltophilia is an emerging multidrug resistant opportunistic pathogen. Nineteen clinical and hospital-environment isolates showed variable abilities to form biofilms. A BALO isolated from the environment preyed upon all strains of S. maltophilia. The predator utilized an epibiotic life cycle and was identified as Bd. exovorus. Bd. exovorus FFRS-5 was able to reduce the mass of biofilms formed by almost all strains of S. maltophilia, even in the presence of ciprofloxacin and/or kanamycin. Thus, Bd. exovorus has the potential to be used therapeutically as an antimicrobial agent. These studies have shed light on the attachment and invasion strategies of BALOs and presented the first potential use of Bd. exovorus as a biocontrol agent.

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