ABSTRACTThe ability to acquire nutrients during infections is an important attribute in microbial pathogenesis. Amino acids are a valuable source of nitrogen if they can be degraded by the infecting organism. In this work, we analyzed histidine utilization in the fungal pathogen of humansCandida glabrata. Hemiascomycete fungi, likeC. glabrataorSaccharomyces cerevisiae, possess no gene coding for a histidine ammonia-lyase, which catalyzes the first step of a major histidine degradation pathway in most other organisms. We show thatC. glabratainstead initializes histidine degradation via the aromatic amino acid aminotransferase Aro8. AlthoughARO8is also present inS. cerevisiaeand is induced by extracellular histidine, the yeast cannot use histidine as its sole nitrogen source, possibly due to growth inhibition by a downstream degradation product. Furthermore,C. glabratarelies only on Aro8 for phenylalanine and tryptophan utilization, sinceARO8, but not its homologueARO9, was transcriptionally activated in the presence of these amino acids. Accordingly, anARO9deletion had no effect on growth with aromatic amino acids. In contrast, inS. cerevisiae,ARO9is strongly induced by tryptophan and is known to support growth on aromatic amino acids. Differences in the genomic structure of theARO9gene betweenC. glabrataandS. cerevisiaeindicate a possible disruption in the regulatory upstream region. Thus, we show that, in contrast toS. cerevisiae,C. glabratahas adapted to use histidine as a sole source of nitrogen and that the aromatic amino acid aminotransferase Aro8, but not Aro9, is the enzyme required for this process.