Deletion of the FLD gene in methylotrophic yeasts Komagataella phaffii and Komagataella kurtzmanii results in enhanced induction of the AOX1 promoter in response to either methanol or formate

Apart from the toxic methanol, relatively safe formic acid and its salts (formates) were shown to act as efficient inducers of the AOX1 promoter in methylotrophic yeasts Komagataella kurtzmanii and K. phaffii. In order to investigate the mechanism of formate induction in the cells of these species, deletion of the formaldehyde dehydrogenase (FLD) gene was carried out, resulting in disruption of the metabolic pathway of methanol dissimilation and thus preventing the intracellular reduction of formate to methanol. The AOX1-lacZ reporter cassette was used to demonstrate that the fld mutation resulted in enhanced induction of the AOX1 by both methanol and formate. This result casts doubt on the hypothesis that methanol is the real inducer of the AOX1 promoter. Alternative mechanisms of induction are discussed.