Fig. 1

Principle of the recombination and ∆fwnA selection system. A Construction of the fwnA deletion mutants in the parental strains A. niger ATNT and tLK01 (ATNT∆akuB). Homologous recombination of the two PCR amplicons into the fwnA locus in the parental strains led to the deletion of the fwnA gene resulting in A. niger strains tLK06 (ATNT∆fwnA) and tLK07 (tLK01∆fwnA). B Representative agar plate of a transformation of the A. niger tLK01 parental strain with the split-marker fwnA deletion constructs. Non-pigmented, fawn colonies are resulting from the fwnA deletion suggesting a successful recombination event whilst pigmented, black colonies indicate false-positive transformants. The frequency of homologous recombination is significantly increased in the A. niger ∆akuB deletion strain tLK01