Mutants of Aspergillus nidulans able to grow at extremely acidic pH acidify the medium less than wild type when grown at more moderate pH.

Mutations conferring the ability to grow on extremely acidic media have been selected in the fungus Aspergillus nidulans and map to at least four genes. The mutations fall into two classes: those that confer acid resistance in media of both high and low buffering capacity and those that confer resistance only in media of low buffering capacity. In growth media of more moderate pH mutations of both classes result in reduced acidification of the medium.