Pichia ciferrii cells and uses thereof

A genetically modified Pichia ciferrii cell, wherein said genetically modified Pichia ciferrii cell comprises, compared to its wild type, a reduced activity of an E1 enzyme encoded by any one of the intron-free nucleic acid sequences selected from the groups consisting of:

• A) SEQ ID NO:
• 3, SEQ ID NO:
• 5, SEQ ID NO:
• 7, SEQ ID NO:
• 9, SEQ ID NO:
• 11;
• and
• B) a sequence which is at least 90% identical to any one of the sequences SEQ ID NO:
• 3, SEQ ID NO:
• 5, SEQ ID NO:
• 7, SEQ ID NO:
• 9, or SEQ ID NO:
• 11, wherein said activity of said E1 enzyme is the catalysis of the reaction 5,10-methylenetetrahydrofolate+L-glycine+H2O to tetrahydrofolate+L-serine.