Identification of Aspergillus niger aquaporins involved in hydrogen peroxide signaling

Aspergillus niger is a robust microbial cell factory for organic acids production. However, the regulation of many industrially important pathways is still poorly understood. Recently the regulation of glucose oxidase (GOx) expression system involved in the biosynthesis of gluconic acid has been uncovered. Hydrogen peroxide, a by-product of the enzymatic conversion of glucose to gluconate, has a pivotal role as a signaling molecule in the induction of this system. In this study, facilitated diffusion of hydrogen peroxide via aquaporin water channels (AQPs) was studied. AQPs are transmembrane proteins of the major intrinsic proteins (MIPs) superfamily. In addition to water and glycerol, they may also transport small solutes such as hydrogen peroxide. Accordingly, the genome sequence of A. niger N402 was screened for putative AQPs. Seven were found which could be classified in three main groups. Their ability to facilitate diffusion of hydrogen peroxide was identified using yeast phenotypic growth assays and by studying AQP gene knock-outs in A. niger. Complementing from both yeast and A. niger experiments, the X-intrinsic protein AQPF plays apparent roles in facilitating hydrogen peroxide transport across cellular membrane. IMPORTANCEAquaporins (AQP) are integral membrane proteins that facilitate transfer of water, small solutes and hydrogen peroxide across the plasma membrane. As they have conserved structural features, it is not difficult to detect their presence in fungal genomes. Their specific roles in fungi are however less understood. Previously we have elucidated the role of the hydrogen peroxide as a second messenger in the induction and regulation of the expression of glucose oxidase involved in the extracellular conversion of glucose in gluconate (1). Here we identified the involvement of AQPF, a member of the X-intrinsic protein class in facilitating transport of the hydrogen peroxide signal across the cell membrane.