Bacteriophages (bacterial viruses) are like bacteria in that they carry genetic information in the form of nucleic acid, reproduce and undergo adaptation in response to environmental pressures. Many bacteriophages are virulent. Virulent bacteriophages invade host cells and lyse the host cells to release progeny bacteriophage particles. Not all bacteriophages are virulent. Pseudotemperate bacteriophages form an unstable carrier state within host cells. Replication of a pseudotemperate bacteriophage is repressed most of the time, and the host cell continues to grow and divide. Pseudotemperate bacteriophages have been described for several types of bacteria.
Pseudotemperate bacteriophages generally contain large genomes. This observation suggests that these bacteriophages may contain genes that are dedicated to functions other than bacteriophage replication and structure. Indeed, at least some types of pseudotemperate bacteriophages significantly alter host cell physiology during the carrier state. Spore-converting bacteriophages are pseudotemperate bacteriophages that have a significant effect on host cell physiology. The DNA of spore-converting bacteriophages becomes trapped within a spore whenever the infected host cell sporulates. Entrapment of the bacteriophage DNA during sporulation provides a selective advantage to the bacteriophage since spores are more resistant to environmental stress than bacteriophage particles. Spore-converting bacteriophages have evolved to enhance the ability of host cells to sporulate so that genome entrapment occurs more frequently. In addition to giving the bacteriophages an advantage, infected cells often sporulate under conditions in which uninfected cells are unable to sporulate. This gives the infected host cell an advantage over uninfected cells in that the infected cells can sporulate under conditions where sporulation would not normally occur. We are using the SP10/Bacillus subtilis (virus/host) system to examine the mechanism of enhanced sporulation in infected bacterial cells. To this end, we are using PCR techniques to search for host related genes on the viral chromosome.
The interaction of spore-converting bacteriophages with spore-forming bacteria suggests that spore-converting bacteriophages and other pseudotemperate bacteriophages form a largely unexplored reservoir of novel genes that could possibly be developed for uses in biotechnology. If pseudotemperate bacteriophages actually alter host cell physiology in favorable ways in the natural environment, then a significant portion of the bacteria in the natural environment should be in a carrier state relationship with one or more pseudotemperate bacteriophages. However, it is not known what percentage of bacteria is infected by pseudotemperate bacteriophages in the natural environment. The approach we have taken involves examination of the interaction of pseudotemperate bacteriophages with host bacteria in the natural environment by determining how frequently infected carrier bacteria occur in the natural environment. We collect soil samples from to areas around the campus and analyze the samples for the presence of infected bacteria.