A unique pattern of toxic synthesis in pentitol catabolism: implications for evolution.

All of our Escherichia coli C mutants blocked in the first step of D-arabitol catabolism (D-arabitol dehydrogenase) became unable to grow in the presence of D-arabitol. We have shown that this sensitivity is eliminated by a defect in the second enzyme of the pathway (D-xylulokinase), leading to a pattern of toxicity and its relief which has not been previously reported. We have found a similar pattern of toxicity and its relief in the closely related ribitol pathway. The evolutionary significance of these findings is discussed.