Genetic redundancy in the catabolism of methylated amines in the yeast Scheffersomyces stipitis

The catabolism of choline as a source ofnitrogen in budding yeasts is thought to proceed viathe intermediates trimethylamine, dimethylamine andmethylamine before the release of ammonia. Thepresent study investigated the utilisation of cholineand its downstream intermediates as nitrogen sourcesin the yeast Scheffersomyces stipitis using a reversegenetics approach. Six genes (AMO1, AMO2, SFA1,FGH1, PICST_49761, PICST_63000) that have previouslybeen predicted to be directly or indirectlyinvolved in the catabolism of methylated amines wereindividually deleted. The growth of each deletionmutant was assayed on minimal media with methylamine,dimethylamine, trimethylamine or choline asthe sole nitrogen source. The two amine oxidaseencodinggenes AMO1 and AMO2 appeared to befunctionally redundant for growth on methylatedamines as both deletion mutants displayed growth onall nitrogen sources tested. However, deletion ofAMO1 resulted in a pronounced growth lag on all fourmethylated amines while deletion of AMO2 onlycaused a growth lag when methylamine was the solenitrogen source. The glutathione-dependentformaldehyde dehydrogenase-encoding gene SFA1was found to be absolutely essential for growth onall methylated amines tested while deletion of the Sformylglutathionehydrolase gene FGH1 caused apronounced growth lag on dimethylamine, trimethylamineand choline. The putative cytochrome P450monooxygenase-encoding genes PICST_49761 andPICST_63000 were considered likely candidates fordemethylation of di- and trimethylamine but producedno discernable phenotype on any of the tested nitrogensources when deleted. This study revealed notable instancesof genetic redundancies in the cholinecatabolic pathway, which are discusse