The field of bacterial phosphorus (P) metabolism has undergone a significant transformation in the past decade owing to the elucidation of widespread and diverse pathways for the metabolism of reduced P compounds. The characterization of these pathways dramatically changes the current and narrow view of P metabolism and our understanding of the forms in which P is produced and available in the environment. In this review, recent investigations into the biochemical pathways and molecular genetics of reduced P metabolism in bacteria are discussed. Particular attention is paid to recently elucidated metabolic reactions and the genetic characterization of biosynthesis of organic reduced P compounds and to the pathways for oxidation of the inorganic reduced P compounds hypophosphite and phosphite.
"Phosphite is more soluble than phosphate, which gives it greater mobility in aquatic environments . Moreover, as a reduced form with relative thermodynamic instability , phosphite can be oxidized to phosphate or reduced to gaseous phosphine (PH 3 , À3)    . As reduction from phosphate is energetically unfeasible, unless phosphite or http://dx.doi.org/10.1016/j.cej.2015.01.113 1385-8947/Ó 2015 Elsevier B.V. All rights reserved. "
[Show abstract][Hide abstract] ABSTRACT: Phosphite is an important intermediate of the phosphorus cycle. Its life in environment is related to its oxidation rate. This paper investigated the photooxidation of phosphite in aqueous solution in the presence of ferric and oxalate ions under a Xe lamp. The photooxidation of phosphite followed pseudo-first-order reaction kinetics. The kinetics constant of 100 μmol L -1 phosphite was 0.0039 min-1 at pH 3 and Fe(III)/Ox 10.0/100.0 μmol L-1. The photooxidation was dependent upon the pH values, phosphite/ferric/oxalate concentration, and light intensity. The decrease of phosphite coincided with the increase of phosphate. The addition of 2-proponal, NaN3 or furfuryl alcohol inhibited the photooxidation of phosphite, which indicated that the yielded reactive oxygen species played an important role in the oxidation of phosphite. The results contribute not only to predict the longevity of phosphite in the aqueous solutions, but also to understand the transfer of phosphite in P cycle.
Chemical Engineering Journal 02/2015; 269. DOI:10.1016/j.cej.2015.01.113 · 4.32 Impact Factor
"Many bacteria have the ability to grow on organophosphonates as a source of phosphorus when the phosphate concentration is very low (White and Metcalf, 2007). In Escherichia coli the metabolism of phosphonates is governed by the set of 14 genes localized with the phn operon (Metcalf and Wanner, 1993). "
[Show abstract][Hide abstract] ABSTRACT: PhnJ from the C-P lyase complex catalyzes the cleavage of the carbon-phosphorus bond in ribose-1-phosphonate-5-phosphate (PRPn) to produce methane and ribose-1,2-cyclic-phosphate-5-phosphate (PRcP). This protein is a novel radical SAM enzyme that uses glycyl and thiyl radicals as reactive intermediates in the proposed reaction mechanism. The overall reaction is initiated with the reductive cleavage of S-adenosylmethionine (SAM) by a reduced [4Fe-4S]1+-cluster to form an Ado-CH2∙ radical intermediate. This intermediate abstracts the proR hydrogen from Gly-32 of PhnJ to form Ado-CH3 and a glycyl radical. In the next step, there is hydrogen atom transfer from Cys-272 to the Gly-32 radical to generate a thiyl radical. The thiyl radical attacks the phosphorus center of the substrate, PRPn, to form a transient thiophosphonate radical intermediate. This intermediate collapses via homolytic C-P bond cleavage and hydrogen atom transfer from the proS hydrogen of Gly-32 to produce a thiophosphate intermediate, methane, and a radical intermediate at Gly-32. The final product, PRcP, is formed by nucleophilic attack of the C2-hydroxyl on the transient thiophosphate intermediate. This reaction regenerates the free thiol group of Cys-272. After hydrogen atom transfer from Cys-272 to the Gly-32 radical, the entire process is repeated with another substrate molecule without the use of another molecule of SAM or involvement from the [4Fe-4S]-cluster again.
"Phosphite is applied to plants in the form of a neutralized soluble potassium phosphite salt by foliar application, trunk injection or a soil drench (Hardy et al. 2001). The use of phosphite for these applications leads to increased levels of phosphonates (phosphite esters) in the environment and in the tissues of plants and animals (White and Metcalf 2007). However, when applied at the recommended rates that result in tissue concentrations of approximately 1 mM, phosphite is considered to be of low toxicity to organisims other than oomycetes (Guest et al. 1995). "
[Show abstract][Hide abstract] ABSTRACT: Phosphite application mitigates diseases caused by oomycete plant pathogens. Tissue concentrations of phosphite above 1 mM are generally required for disease protection. Determining the concentration of phosphite in plant material requires extensive extraction and derivatisation procedures prior to separation by gas–liquid chromatography (GLC). This paper describes a direct chemical method to estimate the concentration of phosphite using a silver nitrate reagent. Glass fiber filter papers were saturated with a 1 M aqueous solution of silver nitrate (adjusted to pH 2.5 with nitric acid) and dried for 2 h at 60 °C. 20 μL of polyvinylpolypyrrolidone treated aqueous plant extract was adsorbed onto the filter paper and incubated in the dark at room temperature (25 °C) for 1 h. The presence of phosphite in the extract reduces the silver ions to elemental silver resulting in a grey-black precipitate that is clearly visible. The method is rapid, sensitive and inexpensive, and can detect phosphite at concentrations of 1 mM in 20 μl of aqueous extract from 100 mg of fresh plant material. Samples analysed by this method gave similar results to analysis by GLC, indicating the method can be used in the field or the laboratory to determine uptake and distribution phosphite in the plant, the retention of phosphite over time and the timing of phosphite reapplication.
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