ESCHERICHIA-COLI IS UNABLE TO PRODUCE PYRROLOQUINOLINE QUINONE (PQQ)

Many bacteria can synthesize the cofactor pyrroloquinoline quinone (PQ Q), a cofactor of several dehydrogenases, including glucose dehydrogen ase (GCD). Among the enteric bacteria, Klebsiella pneumoniae has been shown to contain the genes required for PQQ biosynthesis. Escherichia coli and Salmonella typhimurium were thought to be unable to synthesiz e PQQ but it has been reported that strain EF260, a derivative of E. c oli FB8, can synthesize PQQ after mutation and can oxidize glucose to gluconate via the GCD/PQQ pathway (F. Biville, E. Turlin & F. Gasser, 1991, J Gen Microbiol 137, 1775-1782). We have reinvestigated this cla im and conclude that it is most likely erroneous. (i) Strain EF260, is olated originally by Biville and coworkers, was unable to synthesize a hole-enzyme GCD unless PQQ was supplied to the growth medium. No GCD activity could be detected in membrane fractions. (ii) The amount of P QQ detected in the growth medium of EF260 was very low and not very di fferent from that found in a medium with its parent strain or in a med ium containing no cells. (iii) EF260 cells were unable to produce gluc onate from glucose via the PQQ/GCD pathway. (iv) Introduction of a gcd ::Cm deletion in EF260, eliminating GCD, did not affect glucose metabo lism. This suggested a pathway for glucose metabolism other than the P QQ/GCD pathway. (v) Glucose uptake and metabolism in EF260 involved a low-affinity transport system of unknown identity, followed most likel y by phosphorylation via glucokinase. It is concluded that E. coli can not synthesize PQQ and that it lacks genes required for PQQ biosynthes is.