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

AIMS: Use of molecular techniques for the isolation of bacteria capable of phosphonoacetate mineralization as carbon, phosphorus and energy source. METHODS AND RESULTS: RNA extracts obtained at three different stages of an enrichment selecting for phosphonoacetate degrading bacteria were reverse transcribed using 16S rRNA-specific primers, amplified and analysed by temperature gradient gel electrophoresis (TGGE). This information was used to devise a strategy for the isolation of members of the enrichment that were otherwise difficult to obtain in pure culture. We were able to pull out, in total, four out of the six main microbial cultures that were detected by TGGE. Two of the isolates belonging to Mycobacterium and Agromyces genera were for the first time shown to grow in the presence of phosphonoacetate as sole carbon, phosphorus and energy source releasing almost equimolar levels of inorganic phosphate into the culture medium, and they were shown to exhibit phosphonoacetate hydrolase activity in vitro. CONCLUSIONS: The ubiquity of pseudomonad in degradation processes is more likely a consequence of our ignorance of bacterial requirements and physiology, rather than their possession of unique metabolic properties. SIGNIFICANCE AND IMPACT OF THE STUDY: RT-TGGE analysis can be used to guide the successful isolation of micro-organisms difficult to obtain by culture-dependent methods alone.     

A role for carbon catabolite repression in the metabolism of phosphonoacetate by Agromyces fucosus Vs2

A strain of Agromyces fucosus, designated Vs2, metabolized a range of organophosphonate compounds as sole phosphorus sources for growth and metabolized phosphonoacetate as a sole carbon, energy and phosphorus source for growth. With phosphonoacetate as the sole phosphorus source and a pyruvate carbon source, transient phosphate release to the medium was observed, in contrast to cultures grown with glucose and phosphonoacetate, where no phosphate release to the medium was observed. Carbon catabolite repression, specifically by means of inducer exclusion of phosphonoacetate, was proposed as the mechanism responsible, and phosphonoacetate hydrolase enzyme assays carried out on cell extracts confirmed that induced phosphonoacetate hydrolase activities were indeed higher in cells grown on pyruvate with phosphonoacetate as sole phosphorus source. This phenomenon has not previously been demonstrated in vivo, and must represent a significant metabolic control of organophosphonate metabolism. The catabolite repression phenomenon was also evident when A. fucosus grew on 2-aminoethylphosphonate as sole phosphorus source, allowing demonstration of a third mode of control for biodegradation of this compound. Excision of stained zymogram gel pieces, followed by tryptic digestion and mass spectrometric analysis, allowed the identification of phosphonoacetate hydrolase-derived peptides.     

Conserved core structure and active site residues in alkaline phosphatase superfamily enzymes.

Cofactor-independent phosphoglycerate mutase (iPGM) has been previously identified as a member of the alkaline phosphatase (AlkP) superfamily of enzymes, based on the conservation of the predicted metal-binding residues. Structural alignment of iPGM with AlkP and cerebroside sulfatase confirmed that all these enzymes have a common core structure and revealed similarly located conserved Ser (in iPGM and AlkP) or Cys (in sulfatases) residues in their active sites. In AlkP, this Ser residue is phosphorylated during catalysis, whereas in sulfatases the active site Cys residues are modified to formylglycine and sulfatated. Similarly located Thr residue forms a phosphoenzyme intermediate in one more enzyme of the AlkP superfamily, alkaline phosphodiesterase/nucleotide pyrophosphatase PC-1 (autotaxin). Using structure-based sequence alignment, we identified homologous Ser, Thr, or Cys residues in other enzymes of the AlkP superfamily, such as phosphopentomutase, phosphoglycerol transferase, phosphonoacetate hydrolase, and GPI-anchoring enzymes (glycosylphosphatidylinositol phosphoethanolamine transferases) MCD4, GPI7, and GPI13. We predict that catalytical cycles of all the enzymes of AlkP superfamily include phosphoenzyme (or sulfoenzyme) intermediates.