Role of a major facilitator superfamily transporter in adaptation capacity of Penicillium funiculosum under extreme acidic stress.

Fungal species present in extreme low pH environments are expected to have adapted for tolerance to high H(+) concentrations. However, their adaptability mechanism is unclear. In this study, we isolated an acid-tolerant strain of Penicillium funiculosum, which can grow actively at pH 1.0 and thrived in pH 0.6. A major facilitator superfamily transporter (PfMFS) was isolated from an acid-sensitive random insertional mutant (M4) of the fungus. It encodes a putative protein of 551 residues and contains 14 transmembrane-spanning segments. A targeted mutant (M7) carrying an inactivated copy of PfMFS showed an obvious reduction of growth compared with the wild type (WT) and complementation of M7 with PfMFS restored the wild-type level of growth at pH 1.0. Further data showed that the wild-type showed higher intracellular pH than M7 in response to pH 1. Subcellular localization showed that PfMFS was a cell membrane protein. Homology modeling showed structural similarity with an MFS transporter EmrD from Escherichiacoli. These results demonstrate that the PfMFS transporter is involved in the acid resistance and intracellular pH homeostasis of P. funiculosum.