Nucleic acids from the host bacterium as a major source of nucleotides for three marine bacteriophages

The incorporation of 32~-phosphorus into marine bacteriophage nucleic acid was studied in culture experiments to investigate the source of nucleotides used by the phage. We consistently found that the '2~-specific activity in the phage genome increased during the 11 h incubation and was low relative to the specific activity in the medium, averaging 21% ( + S D 5.9) for the three phage isolates. This was in accordance with a mathematical model where most of the nucleotides for phage DNA synthesis were derived from the host cell nucleic acid rather than de novo synthesis. We propose that this metabolic strategy may be common among marine phages, as an adaptation to a nutrient poor environment. Consequently, the contribution of free DNA to the dissolved fraction through phage lysis of bacteria, may be less that previously thought. Also during radiolabelling of bacteriophages in natural water samples, isotope dilution may be dependent on the specific growth rate of the bacterial host.