Some of the oxygen we breathe today is being produced because of viruses infecting micro-organisms in the world's oceans, scientists heard April 2, 2008 at the Society for General Microbiology's 162nd meeting.

About half the world's oxygen is being produced by tiny photosynthesising creatures called phytoplankton in the major oceans. These organisms are also responsible for removing carbon dioxide from our atmosphere and locking it away in their bodies, which sink to the bottom of the ocean when they die, removing it forever and limiting global warming.

"In major parts of the oceans, the micro-organisms responsible for providing oxygen and locking away carbon dioxide are actually single celled bacteria called cyanobacteria," says Professor Nicholas Mann of the University of Warwick. "These organisms, which are so important for making our planet inhabitable, are attacked and infected by a range of different types of viruses."

The researchers have identified the genetic codes of these viruses using molecular techniques and discovered that some of them are responsible for providing the genetic material that codes for key components of photosynthesis machinery.

"It is beginning to become to clear to us that at least a proportion of the oxygen we breathe is a by-product of the bacteria suffering from a virus infection," says Professor Mann. "Instead of being viewed solely as evolutionary bad guys, causing diseases, viruses appear to be of central importance in the planetary process. In fact they may be essential to our survival."

Viruses may also help to spread useful genes for photosynthesis from one strain of bacteria to another.