Rosa Angélica Rangel-Porras , Sharel P. Díaz-Pérez , Juan Manuel Mendoza-Hernández , Pamela Romo-Rodríguez , Viridiana Alejandre-Castañeda , Marco I Valle-Maldonado , Juan Carlos Torres-Guzmán , Gloria Angélica González-Hernández , Jesús Campos-Garcia , José Arnau , Víctor Meza-Carmen , J. Félix Gutiérrez-Corona
J. Microbiol. 2019;57(7):606-617. Published online June 27, 2019
Mucor circinelloides is a dimorphic Zygomycete fungus that
produces ethanol under aerobic conditions in the presence of
glucose, which indicates that it is a Crabtree-positive fungus.
To determine the physiological role of the alcohol dehydrogenase
(ADH) activity elicited under these conditions, we obtained
and characterized an allyl alcohol-resistant mutant
that was defective in ADH activity, and examined the effect
of adh mutation on physiological parameters related to carbon
and energy metabolism. Compared to the Adh+ strain
R7B, the ADH-defective (Adh-) strain M5 was unable to grow
under anaerobic conditions, exhibited a considerable reduction
in ethanol production in aerobic cultures when incubated
with glucose, had markedly reduced growth capacity in the
presence of oxygen when ethanol was the sole carbon source,
and exhibited very low levels of NAD+-dependent alcohol dehydrogenase
activity in the cytosolic fraction. Further characterization
of the M5 strain showed that it contains a 10-bp
deletion that interrupts the coding region of the adh1 gene.
Complementation with the wild-type allele adh1+ by transformation of M5 remedied all the defects caused by the adh1
mutation. These findings indicate that in M. circinelloides,
the product of the adh1 gene mediates the Crabtree effect,
and can act as either a fermentative or an oxidative enzyme,
depending on the nutritional conditions, thereby participating
in the association between fermentative and oxidative
metabolism. It was found that the spores of M. circinelloides
possess low mRNA levels of the ethanol assimilation genes
(adl2 and acs2), which could explain their inability to grow
in the alcohol.