Mycoplasma and Spiroplasma

Abstract

The genera Mycoplasma and Spiroplasma belong to the mollicutes, a group of Gram-positive firmicutes that lack a cell wall. These bacteria live in close association with their eukaryotic hosts and are characterized by an extreme reduction of the genome. While the members of the genus Mycoplasma infect vertebrates and humans, the Spiroplasma species infect insects and plants and cause severe plant diseases. In both genera, pathogenicity is intimately linked to carbon metabolism. Mycoplasma species affect their hosts by producing hydrogen peroxide, which is generated by two enzymes that use water instead of NAD+ as electron acceptor. Spiroplasma species degrade the sucrose that is present in the host tissues to fructose and glucose. Given that only the fructose is catabolized by the bacteria, the remaining glucose accumulates in the plant and causes damage. The cells of the mollicutes are usually pleomorphic, with a specialized terminal organelle structure. This structure is involved in cell division, movement, and attachment to the host cells. Because of their extreme genome reduction, the mollicutes are workhorses for the identification of the minimal gene set that is required for life. This is the basis for the new research field of synthetic biology.