| Viruses that infect bacteria (bacteriophages) are recognized as the most abundant organisms in the world's oceans, and have been found to exist in every type of marine environment explored. Our understanding of lysogeny and pseudolysogeny in the oceans is in its infancy, and there is virtually nothing known about either process in marine spore-forming bacteria. In this dissertation I have studied the nature of the interaction of &phis;HSIC with its host Listonella pelagia, and the factors which control the lysogenic decision in this organism, the occurrence of lysogeny over a 13 month period in Tampa Bay, Florida, the effects of nutrients on prophage induction by naturally occurring bacterial populations in the Gulf of Mexico, and the influence of prophage on the sporulation process in marine spore-forming bacteria. The interaction between the &phis;HSIC phage and its host Listonella pelagia displayed both lysogenic and pseudolysogenic characteristics. The integration of the phage genome into the host's chromosome, and homoimmunity to superinfection were consistent with a lysogenic interaction with its host, however the copious production of phage in the presence of high host cell growth were consistent with pseudolysogeny. Two environmental factors, salinity and degree of aeration, appeared to influence the lysogenic switch of the &phis;HSIC phage under laboratory conditions. The greatest amounts of phages were produced by the phage-host system at high salinity (67) or high rates of aeration by rapid shaking (300 rpm). The greatest occurrence of lysogeny in Tampa Bay, Florida was during the winter season, coinciding with the times of lowest primary and bacterial production, nutrient input, and water temperature. Prophage induction was not nutrient limited in oligotrophic and mesotrophic Gulf of Mexico water samples, and nutrient amendment of these samples appeared to stimulate lytic production of phage. Comparison of heat resistance and frequency of sporulation between cured and phage-infected strains of the lysogenic spore-forming isolates Bacillus sp. and Bacillus pumilus indicated that the phages were necessary for efficient sporulation. Collectively, these results indicate that lysogeny is an important virus-host interaction in the marine environment, whose occurrence is under the influence of a variety of environmental factors. |
