Spore-forming bacteria (ie. those that undergo sporulation in the face of nutrient starvation) can also be infected with bacteriophages. During sporulation, the bacteriophage genome segregates into the developing endospore, and is thereby protected until germination of the spore occurs (Hemphill and Whitely, 1975). Both sporulation and lysogeny are believed to be adaptations by bacteria and temperate viruses, respectively, to environmental stress, with both of these mechanisms occurring in response to the nutrient status of the host cell (Wilson and Mann, 1997). Viruses that cause bacteria to sporulate at higher frequencies are known as spore-converting bacteriophages. All known spore-converting bacteriophages to date are characterized as pseudotemperate, because they are known to produce turbid plaques while entering into an unstable carrier state with their host cell (Silver-Mysliwiec, and Bramucci, 1990). The entrapment of the viral genome within a spore may provide a selective advantage to the phage by ensuring its future propagation when suitable environmental conditions become available for the host cell. Therefore, it may be advantageous for the phage to enhance the level of sporulation of its host (Silver-Mysliwiec, and Bramucci, 1990).
The presence of lysogeny in marine spore-forming bacteria was investigated during a 2001 research cruise in oligotrophic waters of the Gulf of Mexico. Two spore-forming isolates (Bacillus sp. and Bacillus pumilus, pictured above) produced a significant amount of prophage upon treatment with mitomycin C (109 viruses ml-1, figure at left) in comparison to controls. Isolates treated with furocoumarin plus UV light lost the ability to induce prophage upon treatment with mitomycin C, and the treated strains exhibited considerably less heat resistance than their respective wild-type strains. Additionally, the frequency of sporulation (upon treatment with the sporulation inducing agent decoyinine) was also significantly lower in the chemically treated strains than their respective wild-types. These results suggest that prophage play an important role in the sporulation process of these isolates. The occurrence of spore-forming lysogenic bacteria in the pelagic marine environment has not been demonstrated in the past. Similar selective pressures may have shaped the sporulation and lysogenic responses as mechanisms for survival of unfavorable environmental conditions.
Williamson, S.J. 2003. Lysogeny, pseudolysogeny, and sporulation in the marine environment. Dissertation, University of South Florida. 225 p.
Hemphill, H. E., and H. R. Whiteley. 1975. Bacteriophages of Bacillus subtilis. Bacteriological Reviews. 39: 257-315.
Silver-Mysliwiec, T. H., and M. G. Bramucci. 1990. Bacteriophage-enhanced sporulation: comparison of spore- converting bacteriophages PMB12 and SP10. Journal of Bacteriology. 172: 1948-1953.
Wilson, W.H., and N. H. Mann. 1997. Lysogenic and lytic production in marine microbial communities. Aquat. Microb. Ecol. 13: 95-100.