Enhancement of viral production by addition of nitrogen or nitrogen plus carbon in subtropical surface waters of the South Pacific

We tested the hypothesis that viral production is limited by nutrient availability in oligotrophic subtropical surface waters of the South Pacific. Nutrient (C, N, P) addition experiments were conducted at 2 stations (Stn SX18, 39 degree 60'S, 169 degree 60'W; Stn SX22, 19 degree 60'S, 169 degree 60'W) to examine the responses of viral production ( super(3)H-thymidine incorporation) and related variables in bottle-contained surface waters. At Stn SX18, viral production was enhanced in bottles amended with N and C with concomitant increases in bacterial production and growth, suggesting that both viral and bacterial production were co-limited by N and C. At Stn SX22, additions of N accelerated viral production with no consistent response of bacterial production, which might be an indication that prophage production was induced due to the alleviation in N limitation of host bacteria. In both experiments, nutrient-induced increases in viral production were not accompanied by increases in viral abundance, suggesting a possibility that viral production was balanced by loss. Our results suggest that viral production is limited by the availability of N or N+C in subtropical waters of the South Pacific, implying that viruses affect the mode of nutrient-induced changes in bacterial production and microbial trophic transfers in oligotrophic oceanic waters.