This 1959 study investigated vitamin B6 synthesis by mutant strains of Escherichia coli that respond to vitamin B6 or to serine plus glycine plus glycolaldehyde. The researcher compared vitamin B6 production during growth and in cell suspensions across multiple E. coli strains. Mutant strain B166 synthesized vitamin B6 at levels comparable to wild-type parent strain when grown on serine or glycine plus glycolaldehyde, suggesting these compounds may participate in B6 biosynthesis rather than simply reducing vitamin requirements. Strain 22-99 showed enhanced B6 synthesis when glycolaldehyde was added to amino acid supplementation. Notably, wild-type E. coli strains showed minimal responses to these compounds, indicating the effects were specific to mutant strains with metabolic blocks. Cell suspension experiments demonstrated that depleted B166 cells required glycolaldehyde for B6 synthesis from glucose and ammonia. The findings suggest glycolaldehyde and serine/glycine may be involved in the actual vitamin B6 biosynthetic pathway in these mutants, though indirect roles cannot be excluded. The results could not be replicated in prototrophs, suggesting regulatory differences between wild-type and mutant strains.

Key findings

• Mutant E. coli strains B166 and 22-99 synthesize vitamin B6 at enhanced levels when supplied with serine/glycine plus glycolaldehyde, suggesting these compounds participate in B6 biosynthesis rather than merely sparing the vitamin requirement
• Washed cell suspensions of strain B166 depleted of endogenous substrates require glycolaldehyde for vitamin B6 synthesis from glucose and ammonia, indicating a direct biosynthetic role
• Wild-type E. coli strains show minimal responses to serine, glycine, and glycolaldehyde supplementation for vitamin B6 synthesis, indicating the effects are specific to mutant strains
• Glycolaldehyde acts as an absolute or partial requirement for B6 synthesis in mutant suspensions depending on growth conditions, while serine and glycine enhance but are not absolutely required
• The temperature-sensitive vitamin B6 auxotroph strain DW shows fundamentally different behavior, suggesting multiple distinct mechanisms underlie vitamin B6 auxotrophy in different E. coli mutants