Invasion of the ocean body-snatchers

A paper in Nature today (14 August) reveals that certain ocean viruses invade the cells of cyanobacteria (known as blue-green algae) and use the energy the cells produce through photosynthesis for their own purposes.

Researchers at the University of Warwick, led by Professor Nick Mann, have shown that when the viruses infect the bacteria they inject their genetic material into their host, a transfer that may be temporarily advantageous to the host.

Part of the injected DNA codes for a protein which repairs the damage done to cells by too much light from the sun. Normally, the bacterial cells shut down when this photoinhibition occurs and when their own repair mechanisms cannot keep up with the damage. The viruses thus take responsibility for the repairs, and by keeping the cells alive, use the energy provided via photosynthesis to replicate themselves.

Viruses in general and bacteriophages in particular (the sorts of virus that infect bacteria) are abundant in the oceans. The bacteriophage that infects the bacterium, Synechococcus, in the study is known as S-PM2.

Tiny cyanobacteria (around a micron – one millionth of a meter – in diameter) are responsible in the open ocean for 30 – 90% of photosynthesis. Thus, the infecting viruses may be having major effects on the ecology and chemistry of the marine environment.

Professor Mann said, ‘Our results mean that a proportion of photosynthesis in the ocean might be mediated by viruses. This is an intriguing idea when you consider that roughly 45% of the oxygen we breathe is produced globally by the oceans.’

He added, ‘Whilst there may not be any immediate practical implications, it also shows the ecological importance of viruses for transferring genes horizontally to other species.’

Professor Mann’s studies on gene transfers between viruses and bacteria are part of a major initiative on microbial biodiversity, supported by the Natural Environment Research Council.