A comparison of three bacterial phosphonoacetate hydrolases from different environmental sources

Abstract

Cleavage of the carbon–phosphorus bond of the xenobiotic phosphonoacetate by phosphonoacetate hydrolase represents a novel route for the microbial metabolism of organophosphonates, and is unique in that it is substrate‐inducible and its expression is independent of the phosphate status of the cell. The enzyme has previously only been demonstrated in cell extracts of Pseudomonas fluorescens 23F. Phosphonoacetate hydrolase activity is now reported in extracts of environmental Curtobacterium sp. and Pseudomonas sp. isolates capable of the phosphate‐insensitive mineralization of phosphonoacetate as the sole source of carbon, energy and phosphorus at concentrations up to 40 mmol l−1 and 100 mmol l−1, respectively. The enzymes in both strains were similarly inducible by phosphonoacetate and had a unique specificity for this substrate. However, they differed significantly from each other, and from the previously described Ps. fluorescens 23F enzyme, in respect of their apparent molecular masses, temperature optima, thermostability, sensitivity to inhibition by chelating agents and by structural analogues of phosphonoacetate, and in their affinities for the substrate.

Detection of phosphonoacetate degradation and phnA genes in soil bacteria from distinct geographical origins suggest its possible biogenic origin

“…Phosphonoacetate hydrolase activity was found in all isolates, at levels of 15–25 nmol min −1 mg −1 , with the reaction stochiometry being demonstrable over time for release of both inorganic phosphate and acetate. The temperature maxima for all phosphonoacetate hydrolase activities studied in crude cell extracts fell within the previously reported range for such enzymes, being between 37°C and 65°C (McGrath et al ., 1995; 1999). The pH optima, however, were higher than that reported previously for this enzyme, being pH 9.0 in the newly isolated strains, rather than pH 8.0 as observed for the activity in cell extracts of P. fluorescens 23F.…”

“…Zn 2+ requirement was also confirmed as phosphonoacetate hydrolase activity could be inhibited by the addition of the chelating agent, EDTA, at a final concentration of 1 mM and subsequently recovered following the addition of 1 mM Zn 2+ . These observations are similar to those for phosphonoacetate hydrolase activity previously found in Pseudomonas strains (McMullan and Quinn, 1994; McGrath et al ., 1999). Metal dependence was, however, not clearly demonstrated for a Curtobacterium and a Penicillium strain (McGrath et al ., 1999; Klimek‐Ochab et al ., 2003), which further suggests variation in metal dependence between Pseudomonas strains and others belonging to different taxonomic groups.…”

“…putida 3b was capable of growth and liberation of inorganic phosphate at highest concentrations of phosphonoacetate (near equimolar levels of inorganic phosphate released from 150 mM phosphonoacetate, above which concentration growth yields decreased sharply). Previously, the highest concentration of phosphonoacetate that supported growth as sole source of carbon, energy and phosphorus source was 100 mM for a strain of Pseudomonas isolated by McGrath and colleagues (1999).…”

“…It would therefore appear that culture‐based isolation strategies tend to preferentially select those Pseudomonas species exhibiting phosphonoacetate hydrolase activity, rather than other Gram‐negative bacteria. As there is no other obvious function of phosphonoacetate hydrolase, the ubiquitous nature of the phnA and related genes (McGrath et al ., 1999; Klimek‐Ochab et al ., 2003) is proposed to occur as a consequence of a biogenic origin of phosphonoacetate.…”

RT-TGGE as a guide for the successful isolation of phosphonoacetate degrading bacteria

“…1999; Panas et al. 2006), although the existence of this enzyme, or related enzymatic activities, have also been reported in distant taxonomic groups with the discovery of a Curtobacterium and a Penicillium strain (McGrath et al. 1999; Klimek‐Ochab et al.…”