Viruses in the hydrothermal vents

(by Tinkara Tinta, Nicole Krause and Christian Winter)

Viruses are physically small, but very diverse both in terms of appearance and reproductive cycles. Viruses need a host to reproduce and since they cannot swim, they rely on chance for that key meeting with their host. The chance that a specific virus population meets its proper host organism increases with increasing numbers of hosts. Bacteria and Archaea are numerically the most abundant potential viral host organisms in the sea, and consequently, viruses infecting marine microbes are the most abundant group of viruses found in the ocean. Their abundance ranges from up to 10 million per mL at the surface to around 100,000 per mL in the deep sea. Although viruses can infect every group of organisms on our planet, individual viruses often have evolved to only successfully infect very specific host species. Because numerically abundant host species will be infected more frequently as compared to rarer hosts, the numbers of initially dominant hosts will decline selectively due to the viral attack, allowing rarer hosts to increase in numbers. In this way viral infections are controlling dominant host population dynamics. The consequence of successful viral infection for microbes is often death and the release of tens to hundreds of progeny viruses per host cell. More specifically, by constituting a significant source of mortality for bacterioplankton, viruses influence the cycling of organic carbon and nutrients in the ocean.