Viruses short circuit microbial loop in a freshwater subtropical Australian River

Abstract

Marine studies have shown viral lysis of microorganisms releases DOC. But is the same true for freshwater bacterioplankton and what is the fate of the released DOC? This paper describes the relationship between microbial production and viral abundance in a subtropical river, Australia. In a year study the heterotrophic bacterial production (4 to 7.5 g C per square m per d) consumed more carbon per day than the daily primary production (1.1 g C per square m per d). Hence the ecosystem was net heterotrophic. However, DOC concentration in the water column remained constant but the bacterial populations turned the DOC pool over every few days. Viral abundance (1x10E11 per L) remained 10 times that of the bacteria (0.5x10E10 per L). High specific bacterial growth rates (0.6 to 3.5 per h), constant bacterial and viral abundances suggest that the viral lysis was "short circuiting" the microbial loop by recirculating bacterial DOC. On each pass of the loop more DOC was respired as CO2 so DOC and bacterial biomass was not passed to higher trophic groups.