Rhizopus microsporus var. microsporus

Rhizopus microsporus is a type of fungus. Some strains of these live mainly in the soil Zygomycota can form a symbiotic relationship with intracellular growing bacteria of the genus Burkholderia.

The mold is only capable, in the presence of the bacteria for vegetative reproduction, in which the bacteria are confined in the resulting spores. The bacteria produce the toxin rhizoxin that causes the symptoms of Reiskeimlingsfäule. In this case, the growth of the rice roots is inhibited, which affects the development of the plant and often leads to death. The liberated from the dead plant nutrients are taken up by the two symbiotic partners and used for their own growth. Rhizoxin inhibits cell division in the seedlings by binding to β -tubulin and prevents its polymerization units. Therefore, no new cytoskeleton are built; Cell division is inhibited. Since the toxin acts in most eukaryotic cells, the use of this substance in the treatment of cancer will be studied.

The fungus itself is resistant to the toxin because its β -tubulin has a mutation at the 100th amino acid position, such that this can no longer bind rhizoxin. This mutation was probably a basis for the development of the symbiosis between Rhizopus and Burkholderia.

Other examples of a symbiosis between fungi and bacteria represent blue-green algae lichens, live extracellularly in the cyanobacteria. Cyanobacteria of the genus Nostoc live in an endosymbiosis with the fungus Geosiphon pyriformis.