Abstract: The present invention relates to novel functional amdS genes from A. niger that can be used as dominant and bi-directional selection marker gene in the transformation of organisms. The present invention further relates to the production of a compound of interest in a fungal host cell transformed with the amdS genes of the invention. Preferred fungal host cells are filamentous fungal cells. The amdS genes of the invention provide means for identification of functional homologues in other Aspergillus species.

Abstract: The invention relates to oxalate deficient A. niger strains for the production of a given enzyme, wherein the oxalate deficient strain produces at least the same amount of enzyme as the wild type strain it originates from under the same culture conditions. Preferably, the oxalate deficient A. niger strain produces more enzyme than the wild type strain it originates from under the same culture conditions. More preferably, the oxalate deficient A. niger strain is such that when the strain has been transformed with an expression construct comprising a gene coding for an enzyme, said strain produces at least the amount of the enzyme the wild type strain it originates from would produce under the same culture conditions, when the wild type strain has also been transformed with the same expression construct as the oxalate deficient strain. The invention also relates to method for obtaining such oxalate deficient A. niger strain.