5 - Ecology of Bacteriophages in Nature

Abstract

This chapter deals with the ecology of bacteriophages in nature. Viruses are known to be the most numerically abundant form of life in the surface waters of this planet. Viruses contribute approximately 25% of total bacterial mortality. Differences in phage morphology are reflected in differences in DNA hybridization or restriction patterns for phages sharing a common host. There is also conservation of blocks of viral DNA in morphologically variable phage isolated on the same host. Lysogeny is a common occurrence among marine bacteria, and estimates in natural populations based on mitomycin C induction indicate that less than 10% of the population contains inducible prophage. The ability to detect prophage induction in natural populations has been shown to have a seasonal pattern, with little induction capability in the winter. A variety of environmentally significant pollutants can cause prophage induction, and it may be that during summer months a proportion of the population undergoes induction by indigenous factors. Induction of only a portion of the indigenous bacterial population could result in a doubling of the phage population. Non-indigenous phages play important roles in the study of aquatic microbial ecology.