Phenotypical characterisation of a putative -amino acid transaminase in the yeast Scheffersomyces stipitis

Phylogenetic analysis of class III transaminases in the budding yeasts Lachancea kluyveri, Saccharomyces cerevisiae and Scheffersomyces stipitis identified a hitherto uncharacterised Sch. stipitis transaminase encoded by the PICST_54153 gene, which clustered with previously described -amino butyric acid (GABA) and -alanine transaminases. Deletion of the PICST_54153 gene in Sch. stipitis resulted in a complete loss in the utilisation of -alanine and -ureidopropionic acid as nitrogen sources, while growth on 1,3-diaminopropane displayed a significant lag phase compared to the wild-type control. It was therefore concluded that the Sch. stipitis PICST_54153 gene likely encodes a -alanine transaminase. However, minor growth defects when 1,4-diaminobutane or 1,5-diaminopentane was provided as the nitrogen source suggested that the Picst_54153 transaminase may also participate in the catabolism of other diamine-derived -amino acids. Unexpectedly, the picst_54153 deletion mutant failed to grow on solid minimal medium in the presence of 5mM -alanine even if a preferred nitrogen source was provided.