Dermatophytes cause the majority of superficial mycoses in humans and animals. However, little is known about the pathogenicity of this specialized group of filamentous fungi, for which molecular research has been limited thus far. During experimental infection of guinea pigs by the human pathogenic dermatophyte Arthroderma benhamiae, we recently detected the activation of the fungal gene encoding malate synthase AcuE, a key enzyme of the glyoxylate cycle. By the establishment of the first genetic system for A. benhamiae, specific ⌬acuE mutants were constructed in a wild-type strain and, in addition, in a derivative in which we inactivated the nonhomologous end-joining pathway by deletion of the A. benhamiae KU70 gene. The absence of AbenKU70 resulted in an increased frequency of the targeted insertion of linear DNA by homologous recombination, without notably altering the monitored in vitro growth abilities of the fungus or its virulence in a guinea pig infection model. Phenotypic analyses of ⌬acuE mutants and complemented strains depicted that malate synthase is required for the growth of A. benhamiae on lipids, major constituents of the skin. However, mutant analysis did not reveal a pathogenic role of the A. benhamiae enzyme in guinea pig dermatophytosis or during epidermal invasion of the fungus in an in vitro model of reconstituted human epidermis. The presented efficient system for targeted genetic manipulation in A. benhamiae, paired with the analyzed infection models, will advance the functional characterization of putative virulence determinants in medically important dermatophytes.Dermatophytes represent a group of specialized filamentous fungi which account for the majority of superficial fungal infections. Millions of so-called dermatophytoses, which in many cases are long lasting and difficult to eradicate, are recorded for humans and animals every year (29). As a peculiarity, dermatophytes specifically infect keratinized host structures, such as stratum corneum, hair, and nails. At the molecular level, however, little is known of the nature of the pathogenicity mechanisms in dermatophytes (17,30). This drawback might be related to the fact that these fungi, which grow comparatively slowly under laboratory conditions, have so far not intensively been studied genetically, in contrast to other medically important fungi, such as Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. Full genome sequence information for dermatophytes have been available since only very recently (http://www.broadinstitute.org /annotation/genome/dermatophyte_comparative/MultiHome .html), and genetic tools have hardly been established. As a consequence, in dermatophyte species only a few genes have to date been analyzed by targeted inactivation, i.e., pacC and MDR2 in Trichophyton rubrum (8, 9), Ku80, areA, and Trim4 in Trichophyton mentagrophytes (Arthroderma vanbreuseghemii) (32), and areA in Microsporum canis (31). Specifically constructed dermatophyte mutants have, to our knowledge, not yet been tested ...