Battle of the bugs

The story comes from our friends at the Wellcome Trust who highlight work by Sam Brown of Oxford University's Department of Zoology published in Current Biology today. Our bodies contain a wide range of bacteria which mostly do us no harm. But now and then a bacterium will evolve properties which are potentially deadly to its human host. The big question for evolutionary theory is, 'why?', when killing off its host could mean the bacterium is killing itself. Sam explains: 'For many microbes, living in harmony with their host is the best option, so why do some suddenly turn nasty? Sometimes the answer is obvious - for example, the cold virus makes its host sneeze, helping it spread wider. But for other bacteria and viruses, which do not normally cause disease, the reason isn't at all clear. The team of Oxford and US scientists modelled in mice how the bacterium Streptococcus pneumoniae interacts with other bacteria, showing that competition for space can cause deadlier forms of bacteria to evolve.