Abstract
In Escherichia coli uptake and catabolism of organophosphonates are governed by the phnCDEFGHIJKLMNOP operon. The phnO cistron is shown to encode aminoalkylphosphonate N-acetyltransferase, which utilizes acetylcoenzyme A as acetyl donor and aminomethylphosphonate, (S)- and (R)-1-aminoethylphosphonate, 2-aminoethyl- and 3-aminopropylphosphonate as acetyl acceptors. Aminomethylphosphonate, (S)-1-aminoethylphosphonate, 2-aminoethyl- and 3-aminopropylphosphonate are used as phosphate source by E. coli phn+ strains. 2-Aminoethyl- or 3-aminopropylphosphonate but not aminomethylphosphonate or (S)-1-aminoethylphosphonate is used as phosphate source by phnO strains. Neither phn+ nor phnO strains can use (R)-1-aminoethylphosphonate as phosphate source. Utilization of aminomethylphosphonate or (S)-1-aminoethylphosphonate requires the expression of phnO. In the absence of phnO-expression (S)-1-aminoethylphosphonate is bacteriocidal and rescue of phnO strains requires the simultaneous addition of d-alanine and phosphate. An intermediate of the carbon-phosphorus lyase pathway, 5′-phospho-α-d-ribosyl 1′-(2-N-acetamidoethylphosphonate), a substrate for carbon-phosphorus lyase, was found to accumulate in cultures of a phnP mutant strain. The data show that the physiological role of N-acetylation by phnO-specified aminoalkylphosphonate N-acetyltransferase is to detoxify (S)-1-aminoethylphosphonate, an analog of d-alanine, and to prepare (S)-1-aminoethylphosphonate and aminomethylphosphonate for utilization of the phosphorus-containing moiety.
Highlights
Escherichia coli as well as many other bacterial species are able to use a number of phosphorus-containing compounds as phosphate source
We show that the phnO gene encodes aminoalkylphosphonate N-acetyltransferase, and that this enzyme is essential for the utilization of 1-aminoalkylphosphonates (AmMePn and (S)-1-aminoethylphosphonate (S1AmEtPn)) as phosphate ion (Pi) source by the C–P lyase pathway, and that the enzyme is essential for detoxification of the D-alanine analog S1AmEtPn
N-Acetyltransferase activity of the phnO gene product The amino acid sequences specified by phnO of S. enterica and by phnO of E. coli are 77% identical despite their location within different reaction pathways
Summary
Escherichia coli as well as many other bacterial species are able to use a number of phosphorus-containing compounds as phosphate source. E. coli is capable of utilizing both alkylphosphonates, such as methyl- (MePn), ethyl- (EtPn) and propylphosphonate (PrPn) as well as aminoalkylphosphonates, such as aminomethyl- (AmMePn), 2-aminoethyl- (2AmEtPn) and 3-aminopropylphosphonate (3AmPrPn) as Pi source Utilization of both types of phosphonate is dependent on an ATP-binding cassette transport system (encoded by phnCDE) [1,3], as well as two additional apparent nucleotide-binding domains for organophosphonate transport (encoded by phnK and phnL) [1], the enzymes C–P lyase (encoded by phnJ and presumable phnGHI) [1,4], PhnM [5], a-D-ribosyl 1,5-bisphosphate phosphokinase (encoded by phnN) [6] and phosphoribosyl cyclic phosphodiesterase (encoded by phnP) [7]. S. enterica contains the enzyme phosphonoacetaldehyde phosphohydrolase, which is encoded by the phnX gene [10], and which is responsible for the catabolism of 2AmEtPn
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