Date of Award

Spring 2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Ocean and Earth Sciences

Committee Director

Fred C. Dobbs

Committee Member

Wayne Hynes

Committee Member

Alexander Bochdansky

Call Number for Print

Special Collections LD4331.O35 T42 2015

Abstract

The scale of predator-prey interactions varies from the iconic (e.g., lions and gazelles) to the microscopic (e.g., protists and bacteria). Bdellovibrio-and-like-organisms (BALOs) are bacteria that prey upon other Gram-negative bacteria, including pathogens. In particular, the halophilic genus Vibrio, many species of which are disease agents, has been shown to be susceptible to attack by BALOs. One motivation of the present research is to assess the potential for biocontrol of Vibrio by Bacteriovorax. This investigation is the first to test the susceptibility of Vibrio strains (n = 26) originating from a variety of geographic locations to predation by three phylogenetically distinct Bacteriovorax clusters.

In suspension experiments, I used the change in optical density after three days to indicate predation. In 77 of 78 trials, optical density decreased over three days (mean OD decrease = -0.229, st. dev. = 0.09). Additionally, I used quantitative real-time PCR to measure the copy numbers of predator and prey in the same co-cultures. In 77 of 78 trials, copy number of the predators increased over three days, indicating their abundant growth. During the same time, copy number of the prey decreased as they were consumed. The cluster Ill strain reduced 23 of 26 Vibrio strains and the cluster IX and XI strains all but one strain each. Among those vibrios for which the extent of predation extent was low, none were in common among the three predator strains. In parallel experiments, I selected 10 Vibrio strains most susceptible to Bacteriovorax attack in suspension, and investigated their resistance to predation when they had formed biofilms. Inferred from a 5-day change in optical density, cluster Ill significantly reduced biofilms of 5 of the 10 Vibrio strains, cluster IX reduced 3 strains, and cluster XI reduced only 1 Vibrio strain. The most predacious Bacteriovorax in the biofilm experiments was the cluster III strain, whereas in the suspension experiments, it was the cluster XI strain. Given multiple differences in methods, direct comparisons between results of suspension and biofilm experiments are not possible. Overall, however, Bacteriovorax exhibited strong predation of vibrios in suspension and weaker predation in biofilm.

These results, as well as those of other researchers, are encouraging for the prospective use of Bacteriovorax for economic and human health benefits. Especially when combined in cluster pairs, Bacteriovorax may serve as a probiotic or antibiotic against environmental Vibrio in suspension and biofilm.

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DOI

10.25777/r9r1-r268

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