Differences between Cryptococcus neoformans and Cryptococcus gattii in the Molecular Mechanisms Governing Utilization of D-Amino Acids as the Sole Nitrogen Source

PLoS One. 2015 Jul 1;10(7):e0131865. doi: 10.1371/journal.pone.0131865. eCollection 2015.

Abstract

The ability to grow on media containing certain D-amino acids as a sole nitrogen source is widely utilized to differentiate Cryptococcus gattii from C. neoformans. We used the C. neoformans H99 and C. gattii R265 strains to dissect the mechanisms of D-amino acids utilization. We identified three putative D-amino acid oxidase (DAO) genes in both strains and showed that each DAO gene plays different roles in D-amino acid utilization in each strain. Deletion of DAO2 retarded growth of R265 on eleven D-amino acids suggesting its prominent role on D-amino acid assimilation in R265. All three R265 DAO genes contributed to growth on D-Asn and D-Asp. DAO3 was required for growth and detoxification of D-Glu by both R265 and H99. Although growth of H99 on most D-amino acids was poor, deletion of DAO1 or DAO3 further exacerbated it on four D-amino acids. Overexpression of DAO2 or DAO3 enabled H99 to grow robustly on several D-amino acids suggesting that expression levels of the native DAO genes in H99 were insufficient for growth on D-amino acids. Replacing the H99 DAO2 gene with a single copy of the R265 DAO2 gene also enabled its utilization of several D-amino acids. Results of gene and promoter swaps of the DAO2 genes suggested that enzymatic activity of Dao2 in H99 might be lower compared to the R265 strain. A reduction in virulence was only observed when all DAO genes were deleted in R265 but not in H99 indicating a pathobiologically exclusive role of the DAO genes in R265. These results suggest that C. neoformans and C. gattii divergently evolved in D-amino acid utilization influenced by their major ecological niches.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Amino Acids / metabolism*
  • Animals
  • Cryptococcosis / microbiology
  • Cryptococcus gattii / metabolism*
  • Cryptococcus gattii / pathogenicity
  • Cryptococcus neoformans / metabolism*
  • Cryptococcus neoformans / pathogenicity
  • D-Amino-Acid Oxidase / genetics
  • D-Amino-Acid Oxidase / metabolism
  • Mice
  • Nitrogen / metabolism*
  • Promoter Regions, Genetic
  • Virulence

Substances

  • Amino Acids
  • D-Amino-Acid Oxidase
  • Nitrogen