Virus-induced transfer of organic carbon between marine bacteria in a model community

Abstract

Viral lysis results in the transformation of living cells into dissolved and colloidal organic matter referred to as lysate. When viruses are included in food web models it is generally assumed that lysates are readily metabolized by bacteria in the community. We hypothesized that the produc- tion of lysate by viruses could also influence microbial community composition by mediating the diversification of carbon sources. To test this hypothesis, we established simple model communities containing various combinations of 2 marine bacteria (Cellulophaga sp. and Photobacterium sp.) and 2 viruses (one specific to each bacterial type) grown in a seawater-based medium with lactose as the sole carbon source. This medium supported vigorous growth of Cellulophaga sp., but not of Photo- bacterium sp. In control experiments, where Photobacterium sp. was cultured with either Cellu- lophaga sp. or Cellulophaga-specific virus, the biomass of Photobacterium sp. increased by 50% or less. In contrast, the Photobacterium sp. biomass significantly increased by 8-fold (p < 0.001, n = 3) in co-cultures with the Cellulophaga sp. virus-host pair. These data indicate that the substrate support- ing growth by Photobacterium sp. was primarily Cellulophaga lysate and not material introduced with the host and virus inocula nor material secreted by Cellulophaga during normal growth. Estimates of the trophic transfer suggested that 28% of the Cellulophaga sp. lysate was converted into new bacterial biomass, which indicated that at least 62% of the lysate was metabolized by Photobacterium sp. Our results from this simple marine model community illustrate that the activity of a virus-host system can effect the transfer of organic material from one bacterial type to another whose growth would otherwise be limited by a lack of suitable substrates.