Movement of viruses between biomes

Abstract

Viruses are abundant in all known ecosystems. In the present study, we tested the possibility that viruses from one biome can successfully propagate in another. Viral concentrates were prepared from different near-shore marine sites, lake water, marine sediments, and soil. The concentrates were added to microcosms containing dissolved organic matter as a food source (after filtration to allow 100-kDa particles to pass through) and a 3% (vol/vol) microbial inoculum from a marine water sample (after filtration through a 0.45-microm-pore-size filter). Virus-like particle abundances were then monitored using direct counting. Viral populations from lake water, marine sediments, and soil were able to replicate when they were incubated with the marine microbes, showing that viruses can move between different ecosystems and propagate. These results imply that viruses can laterally transfer DNA between microbes in different biomes.

FIG. 1.

Filtrates (A) and basic experimental protocol (B) used in this paper. In the mixing experiments (e.g., Fig. 3), the basic experimental procedure was modified by adding 1 ml of a 100× viral concentrate to 100 ml of the DOM fraction in place of the VLP fraction.

FIG. 2.

Marine viral community propagation requires an initial viral concentration of >3%, vol/vol, of the natural viral community concentration. Samples from the same carboy (A) and from different carboys but the same site (B) were tested to determine variation by this method. VLP numbers were determined by using direct counting (SYBR Gold epifluorescence microscopy).

FIG. 3.

Viral communities from different sites were able to propagate on marine microbes. (A) Viral communities from different marine sites were mixed with microbes from MB and the LJ Cove, and VLP numbers were monitored over time. (B) Nonmarine viral communities were added to marine microbial communities, and VLP numbers were monitored over time. MICR, microbial community source; VLP, viral community source. The number of VLPs was determined by epifluorescence microscopy direct counting with SYBR Gold.

FIG. 4.

VLP production is dependent on the presence of a microbial community. Marine and nonmarine viral concentrates were mixed with MB microbes (MICR + VLP + DOM) or placed in MB seawater that had been filtered to allow 100-kDa particles to pass through (VLP + DOM). VLP numbers were determined after 84 h by use of direct counting. In all cases, the VLP concentrations were higher in microcosms containing the MICR fraction. When no MICR fraction was added to the viruses, virus degradation rates ranged from 5.1 × 10⁶ to 2.5 × 10⁴ day⁻¹ (data not shown). OBSed, sediment from OB; LMSoil, soil from LM Park.