Pichia ciferrii cells and use thereof

An genetically modified Pichia ciferrii cell, wherein said genetically modified Pichia ciferrii cell has, compared to its wild type, a reduced activity of an E1 enzyme encoded by the intron-free nucleic acid sequences selected from the group consisting of

• A) SEQ ID NO:
• 1, and
• B) a sequence which is at least 90% identical to SEQ ID NO:
• 1, wherein said activity of said E1 enzyme is the catalysis of the reaction 5,10-methylenetetrahydrofolate+L-glycine+H2O to tetrahydrofolate+L-serine.