Three bacterial strains, Agrobacterium radiobacter, Klebsiella oxytoca, and Kluyvera ascorbata, isolated by enrichment culture for carbon to phosphorus bond cleavage ability, were analyzed for the mode of CP bond fission. The cleavage of alkyl phosphonic acids to alkanes and inorganic phosphates proceeded both aerobically and anaerobically, and growth on trideuteromethylphosphonic acid yielded trideuteromethane as product. These data indicate that functionalization of the organic moiety does not precede carbon to phosphorus bond cleavage. As probes for radical intermediates, cyclopropylmethylphosphonic acid and cis-1,2-dideutero-1-propenylphosphonic acid were used in growth experiments and the gaseous hydrocarbon products were examined. With the cyclopropylmethylphosphonic acid probe, all three bacteria produced methylcyclopropane, but only K. oxytoca and K. ascorbata also generated the acyclic olefin 1-butene, and then only in very low quantity (0.6 and 0.3% versus methylcyclopropane, respectively). With the propenylphosphonic acid probe, cis-1,2-dideuteropropene was formed with greater than 98% retention of configuration with each bacterial strain. Only for K. oxytoca was the alternate product, in this case trans-1,2-dideuteropropene, clearly detected at 1.5%. Thus, CP bond fission may yield radical intermediates that are trapped efficiently at the enzyme active site or, alternatively, homolysis of the CP bond may occur as a minor reaction pathway.
Bibliographical noteFunding Information:
This work was supported in part by a grant from the National Institutes of Health (GM 20011). Funds to purchase and maintain the microwave spectrometer were provided by the National Science Foundation. S.L.S. and L.P.W. are recipients of National Institutes of Health Postdoctoral Fellowships. The authors thank Dr. Alan Walts for many helpful discussions and Drs. Tim Miller and Thomas Neenan (Harvard University, Cambridge, MA) for their assistance in the GC-MS experiment.