Bacterial species forced to cooperate to keep itself alive
When threatened with starvation, groups of cells of the social bacterium Myxococcus xanthus (M. xanthus) work together to create spore-bearing 'fruiting bodies' that are resistant to stress. Findings from a study into the phenomenon are published in the journal Current Biology. Researchers from the Netherlands Institute of Ecology and Indiana University in the US introduce their results by acknowledging that research has been undertaken by other scientists in the past on social interactions among microbes that engage in cooperative behaviour. The problem, they point out, is that 'little is known about the scales at which initially cooperative microbes diversify into socially conflicting genotypes in nature.' The focus of the team's study was M. xanthus, a predatory soil bacterium that kills and consumes other microbes by secreting toxic compounds. When food is in short supply and the bacteria are threatened with starvation, groups of cells cooperate to form types of fruiting bodies. The role of some of the cells is to build the structure of the fruiting body, while the role of others is to become spores to aid survival. Dr Gregory Velicer from Indiana University explained that in some social microbes cooperation takes place mainly among identical or very similar cells. This occurs in order to compete against relatively unrelated individuals. 'This is unlike humans, who are more likely to cooperate with unrelated individuals as well as with close kin. In the bacteria we study, cooperation appears to be highly restricted,' added Dr Velicer. According to the team, M. xanthus cells are able to recognise the smallest genetic differences in one another, differences that even the scientists themselves struggle to identify. In the study, the researchers paired M. xanthus strains taken just centimetres apart to gauge whether the reaction would be one of cooperation or competition. They discovered that even for the strains that lived on the same soil sample and were almost genetically identical, the existing deviation was great enough to impede one another's ability to produce spores. The team also concluded that competition was fiercest among bacteria taken from distant locations. Cooperation between the cells may, therefore, be more likely motivated by necessity rather than willingness. According to Dr Velicer, for the next phase of the study he would like to pair closely related strains and perform a comprehensive assessment of specific genetic differences that produce antagonism and social exclusion. Ultimately, he added, the goal would be to determine how new species of social bacteria might evolve in a geographical area shared with a parental species. He concluded: 'If strong social incompatibilities evolve rapidly, that has implications for understanding how interacting strains diverge over long periods of time.'
Countries
Netherlands