Authors: Kakuta Eri Isao Kudo
Publish Date: 2015/08/18
Volume: 72, Issue: 2, Pages: 177-187
Abstract
A modified dilution experiment was conducted to evaluate the relative contribution of viral lysis and protozoan grazing to the mortalities of heterotrophic bacteria in Funka Bay a subarctic coastal bay The experiment included the stepwise dilution of the original seawater with virusfree seawater 10 kDa ultrafiltered to change the encounter rate of both virus and protozoa to heterotrophic bacteria incubation for 48 h and monitoring the change in the abundance of heterotrophic bacteria In a parallel experiment the original seawater was replaced by 10 µm fractionated seawater to eliminate protozoa and the same dilution was conducted with the virusfree seawater to estimate only lytic mortality The viral lysis and protozoan grazing rates in the surface water ranged from 040 to 119 and 008 to 027 days−1 respectively Viral lysis was the main cause for the bacterial mortality 798 ± 32 The net in situ growth rate of heterotrophic bacteria was about 015 days−1 In the bottom water 90 m both mortalities were lower than those at the surface and the net growth rate was mostly a negative value The contribution of released dissolved organic matter DOM through lysis to the bacterial carbon demand BCD was evaluated The lysed bacterial cells might release DOM to the ambient environment in which bacterial organic matter is recycled in the subsequent bacterial production The potential contribution was estimated to range from 25 to 27 in the surface water and to be 31 in the bottom water suggesting that the lytic mortality significantly fueled DOM to the subsequent bacterial production
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