An international team including researchers from the Max Planck Institute for Chemical Ecology has described a bacterium residing in a species of leaf beetles which has an unexpected feature: it provides the beetle with the enzymes required to break down certain plant cell wall components. The genome of the bacterium is the smallest ever sequenced of any organism living outside a host cell. It contains genes that are responsible for the production of pectinases, the enzymes that break down pectin, an essential component of the plant cell wall. The production of pectinases is therefore the primary function of these bacteria. Without bacterial symbionts the beetles could not to gain access to the nutrients inside the plant cells and hence would be unable to survive. The study is reported today in Cell.