Utilization of organophosphonates by environmental microorganisms

A survey of the utilization by environmental micro-organisms of a range of compounds containing the carbon-phosphorus (C-P) bond was carried out. Elective culture studies indicated that 15 of 19 alkylphosphonates tested served only as a sole source of phosphorus for microbial growth. Their metabolism did not lead to the extracellular release of inorganic phosphate. However, four organophosphonates - phosphonoacetate, phosphonoalanine, 2-aminoethylphosphonate and phosphonomycin - supported microbial growth when supplied as either a phosphorus source or as a carbon and energy source, with near-quantitative inorganic phosphate release. Four of five amino alkylphosphonates tested were also utilized as a nitrogen source in the presence of 1 mmol l(-1) inorganic phosphate. In a subsequent screening programme, 99% of bacterial isolates tested were able to utilize 2-aminoethylphosphonate as a sole phosphorus source, 61% as a nitrogen source, 10% as a source of nitrogen and phosphorus, and 2% as a source of carbon, nitrogen and phosphorus; 2% of isolates used phosphonoalanine as a nitrogen source. These results suggest that the uptake and metabolism of organophosphonates by bacteria is less 'tightly' regulated by phosphorus starvation than has previously been supposed.

Biotransformation of Substituted Pyridines with Dioxygenase-containing Microorganisms.

A series of 2-, 3- and 4-substituted pyridines was metabolised using the mutant soil bacterium Pseudomonas putida UV4 which contains a toluene dioxygenase (TDO) enzyme. The regioselectivity of the biotransformation in each case was determined by the position of the substituent. 4-Alkylpyridines were hydroxylated exclusively on the ring to give the corresponding 4-substituted 3-hydroxypyridines, while 3-alkylpyridines were hydroxylated stereoselectively on C-1 of the alkyl group with no evidence of ring hydroxylation. 2-Alkylpyridines gave both ring and side-chain hydroxylation products. Choro- and bromo-substituted pyridines, and pyridine itself, while being poor substrates for P. putida UV4, were converted to some extent to the corresponding 3-hydroxypyridines. These unoptimised biotransformations are rare examples of the direct enzyme-catalysed oxidation of pyridine rings and provide a novel synthetic method for the preparation of substituted pyridinols. Evidence for the involvement of the same TDO enzyme in both ring and side-chain hydroxylation pathways was obtained using a recombinant strain of Escherichia coli (pKST11) containing a cloned gene for TDO. The observed stereoselectivity of the side-chain hydroxylation process in P. putida UV4 was complicated by the action of an alcohol dehydrogenase enzyme in the organism which slowly leads to epimerisation of the initial (R)-alcohol bioproducts by dehydrogenation to the corresponding ketones followed by stereoselective reduction to the (S)-alcohols.