Viruses in phosphorus-starved regions of the ocean can take advantage of bacteria, which needs phosphorus as a nutrient. The bacteria use viruses only to have the virus inject its own DNA into the bacteria, which results in the host bacterium exploding after about 10 hours.
Researches have found out how the viruses use bacteria to support the replication of their own DNA. They have discovered that photosynthetic ocean bacteria should beware of viruses as these viruses are carrying genetic material, which is taken from their previous bacterial hosts that tricks the new host into using its own machinery to activate the genes.
The virus senses the host’s stress and offers what seems like a helping hand, bacterial genes nearly identical to the host’s own that enable the host to gather more phosphorus. The host uses these genes, but the additional phosphorus goes towards supporting the virus’s replication of its own DNA.
Once that process is completed, about 10 hours after infection, the virus explodes its host, releasing progeny viruses back into the ocean where they can invade other bacteria and repeat the same process. The additional phosphorus-gathering genes provided by the virus keep its reproduction cycle on schedule.
The virus is choosing a very sophisticated component of the host’s regulatory machinery for enhancing its own reproduction. The phages have evolved the capability to sense the degree of phosphorus stress in the host they’re infecting and have captured, over evolutionary time, some components of the bacteria’s machinery to overcome the limitation.
This research was performed using the bacterium Prochlorococcus and Synechococcus, which together produces about one-sixth of the oxygen in Earth’s atmosphere. Prochlorococcus is about one micron in diameter and can reach densities of up to 100 million per liter of seawater. Synechococcus is only slightly larger and less abundant.
The bacterial mechanism is a two-component regulatory system that refers to the microbe’s ability to respond to external environmental conditions. This system prompts the bacteria to produce extra proteins that bind to phosphorus and bring it into the cell. The gene carried by the virus encodes this same protein.
The research indicates that the phage which infects these bacteria has evolved right along with their hosts.
The whole system is a bit of evidence for the incredible intimacy of the relationship between phage and host. Most of what we understand about phage and bacteria has come from model microorganisms used in biomedical research. The environment of the human body is dramatically different from that of the open oceans, and these oceanic phages have much to teach us about fundamental biological processes.