Deinococcus radiodurans, an extremely radioresistant bacterium, synthesizes coenzyme pyrroloquinoline-quinone (PQQ) but exhibits a negative phenotype for mineral phosphate solubilization. Gene for the putative PQQ synthesizing protein was PCR amplified and cloned from Deinococcus, sequenced, and expressed in Escherichia coli, under an inducible E coli promoter. The transgenic E. coli expressed PQQ synthase protein of 42 kDa and complemented the mineral phosphate solubilization phenotype of E coli, suggesting the synthesis of an active protein. The cells expressing high levels of this protein showed increased protection against photodynamically produced reactive oxygen species. The effect could be attributed to the upregulation of antioxidant enzymes such as catalase and superoxide dismutase by PQQ in transgenic E coli through an unknown mechanism. The study elucidates a hitherto unknown possible function of PQQ in bacteria. (C) 2003 Elsevier Inc. All rights reserved.