Non-circadian light inducible rhythm in Aspergillus nidulans.

Aspergillus nidulans grown under standard laboratory conditions does not show circadian rhythmic growth. The presence of a circadian clock was demonstrated in A. nidulans at the level of gene expression (Greene et al. 2003), but a visually observable rhythm is lacking. We recently observed a remarkable rhythmic growth pattern in the formation of conidiospores and ascospores in a fludioxonil resistant mutant of A. nidulans (fldA1) grown in a dark incubator. This is reminiscent of a circadian rhythm. We found however that our observed rhythm is induced by light (leaking into the ‘dark’ incubator) and is not self-sustainable. In absolute darkness or constant light the rhythm is lost; therefore, we conclude that the rhythm is not a true intrinsic circadian rhythm.