Bacteria and fungi are found in different phylogenetic domains, but often live in close proximity with each other, competing for the same ecological niche. One of the more familiar examples of fungal-bacterial antagonism is the fungal suppression of bacteria by production of antibiotic substances such as penicillin. Recent discoveries of mutually beneficial fungal-bacterial interactions challenge the conventional view that fungi and bacteria are natural enemies. However, the mechanisms responsible for these positive relationships are poorly understood. A recent study led by Cornell University and DOE JGI researchers found that in one such interaction between a mold fungus Rhizopus microsporus and its Burkholderia endosymbiont, lipid metabolism of the fungus determines whether the interaction has a positive or a negative outcome.
Rhizopus microsporus is a soil saprotroph responsible for food spoilage and pathogenesis of plants and immunocompromised humans. The Burkholderia symbiont synthesizes a potent toxin that facilitates plant pathogenesis. The endobacteria, in turn, benefit from energy provision by the host. This study shows that when interacting with the endobacteria, host fungi show a dramatic increase in particular lipid metabolism genes. Inhibition of the lipid pathway in question blocks development of the symbiosis. Remarkably, the key lipid metabolism genes activated during symbiosis are unique to early divergent fungi. These new findings are important for understanding how fungal-bacterial mutualisms evolve and for future applications of oleaginous molds in biodiesel production.
Lastovetsky, O.A., Gaspar, M.L., Mondo, S.J., LaButti, K.M., Sandor, L., Grigoriev, I.V., Henry, S.A., and Pawlowska, T.E. 2016. Lipid metabolic changes in an early divergent fungus govern the establishment of a mutualistic symbiosis with endobacteria. Proceedings of the National Academy of Sciences.