Studies on the biodegradation of fosfomycin: growth of Rhizobium huakuii PMY1 on possible intermediates synthesised chemically

Efficient degradation and detoxification of antibiotic Fosfomycin by UV irradiation in the presence of persulfate

Fosfomycin (FOS) as a widely used antibiotic has been found in abundance throughout the environment, but little effort has been devoted to its treatment. In this study, we systemically looked into the degradation of FOS by ultraviolet-activated persulfate (UV/PS) in aqueous solutions. Our findings demonstrated that FOS can be degraded efficiently under the UV/PS, e.g., >90 % of FOS was degraded with 19,200 mJ cm-2 of UV irradiance and 20 μM of PS. HO was the dominant radical responsible for FOS degradation. FOS degradation increased as PS dosage increased, and higher degradation efficiency was observed at neutral pH. Natural water constitutes either promoted (e.g., Cu2+, Fe3+, and SO42-) or inhibited (e.g., humic acid, HCO3-, and CO32-) FOS degradation to varying degrees. Hydroxyl substitution, CP bond cleavage, and coupling reactions were the major degradation pathways for FOS degradation. Finally, the toxicity evaluation revealed that FOS was toxic to E. coli and S. aureus, but the toxicity of the intermediate products of FOS to E. coli and S. aureus rapidly decreased over time after UV/PS treatment. Therefore, these findings provided a fundamental understanding of the transformation process of FOS and supplied useful information for the environmental elimination of FOS contamination and its toxicity.

Biosynthesis of the Fungal Organophosphonate Fosfonochlorin Involves an Iron(II) and 2-(Oxo)glutarate Dependent Oxacyclase

The fungal metabolite Fosfonochlorin features a chloroacetyl moiety that is unusual within known phosphonate natural product biochemistry. Putative biosynthetic genes encoding Fosfonochlorin in Fusarium and Talaromyces spp. were investigated through reactions of encoded enzymes with synthetic substrates and isotope labelling studies. We show that early biosynthetic steps for Fosfonochlorin involves the reduction of phosphonoacetaldehyde to form 2-hydroxyethylphosphonic acid, followed by oxidative intramolecular cyclization of the resulting alcohol to form ( S )-epoxyethylphosphonic acid. The latter reaction is catalyzed by FfnD, a rare example of a non-heme iron / 2-(oxo)glutarate dependent oxacyclase. In contrast, FfnD behaves as a more typical oxygenase with ethylphosphonic acid, producing ( S )-1-hydroxyethylphosphonic acid. FfnD thus represents a new example of a ferryl generating enzyme that can suppress the typical oxygen rebound reaction that follows abstraction of a substrate hydrogen by a ferryl oxygen, thereby directing the substrate radical towards a fate other than hydroxylation.

Stereochemical Course of Methyl Transfer by Cobalamin-Dependent Radical SAM Methyltransferase in Fosfomycin Biosynthesis

The methyl groups of [ methyl-( S)]- and [ methyl-( R)]-[ methyl-D,T]-l-methionine fed to Streptomyces fradiae were incorporated into fosfomycin, which was chemically degraded to chiral AcONa. The enzymatic test gave the ( S)-configuration for the chiral AcONa derived from methionine with the ( S)-[D,T]methyl group ( F = 31.7) and ( R) for the one derived from methionine with the ( R)-[D,T]methyl group ( F = 83.0). The radical SAM methyltransferase transfers the methyl group of MeCbl to HEP-CMP with inversion of configuration.

Re2 O7 -Mediated Dehydrative Cyclization Reactions: Total Synthesis of Herboxidiene and Its 12-Desmethyl Analogue

Re₂ O₇ catalysis effects efficient and stereoselective dehydrative cyclization reactions from monoallylic diols, with stereocontrol arising from thermodynamic equilibration. This method was applied to a rapid synthesis of the spliceosome inhibitor herboxidiene. The route was also utilized for the synthesis of an analogue that highlights the importance of a single methyl group in biasing the conformation in the acyclic region of the molecule.

Towards the biodegradation pathway of fosfomycin

Three functionalised propylphosphonic acids were synthesised to study C-P bond cleavage in R. huakuii PMY1. (R)-1-Hydroxy-2-oxopropylphosphonic acid [(R)-5] was prepared by chiral resolution of (±)-dimethyl 1-hydroxy-2-methylallyllphosphonate [(±)-12], followed by ozonolysis and deprotection. The N-(l-alanyl)-substituted (1R,2R)-2-amino-1-hydroxypropylphosphonic acid 10, a potential precursor for 2-oxopropylphosphonic acid (5) in cells, was obtained by coupling the aminophosphonic acid with benzotriazole-activated Z-l-alanine and hydrogenolytic deprotection. (1R*,2R*)-1,2-Dihydroxy-3,3,3-trifluoropropylphosphonic acid, a potential inhibitor of C-P bond cleavage after conversion into its 2-oxo derivative in the cell, was accessed from trifluoroacetaldehyde hydrate via hydroxypropanenitrile 21, which was silylated and reduced to the aldehyde (±)-23. Diastereoselective addition of diethyl trimethylsilyl phosphite furnished diastereomeric α-siloxyphosphonates. The less polar one was converted to the desired racemic phosphonic acid (±)-(1R*,2R*)-9 as its ammonium salt.

Recent advances in Michael addition of H-phosphonates

The review discusses recent achievements in the development of more environmentally friendly and economically competitive processes for the synthesis of biologically and synthetically important phosphorus-bearing compounds by conjugate addition of hydrogen-phosphonates to different Michael acceptors.

Organophosphonates revealed: new insights into the microbial metabolism of ancient molecules

Organophosphonates are ancient molecules that contain the chemically stable C-P bond, which is considered a relic of the reducing atmosphere on primitive earth. Synthetic phosphonates now have a wide range of applications in the agricultural, chemical and pharmaceutical industries. However, the existence of C-P compounds as contemporary biogenic molecules was not discovered until 1959, with the identification of 2-aminoethylphosphonic acid in rumen protozoa. Here, we review advances in our understanding of the biochemistry and genetics of microbial phosphonate metabolism, and discuss the role of these compounds and of the organisms engaged in their turnover within the P cycle.

The genes and enzymes of phosphonate metabolism by bacteria, and their distribution in the marine environment

Phosphonates are compounds that contain the chemically stable carbon–phosphorus (C–P) bond. They are widely distributed amongst more primitive life forms including many marine invertebrates and constitute a significant component of the dissolved organic phosphorus reservoir in the oceans. Virtually all biogenic C–P compounds are synthesized by a pathway in which the key step is the intramolecular rearrangement of phosphoenolpyruvate to phosphonopyruvate. However C–P bond cleavage by degradative microorganisms is catalyzed by a number of enzymes – C–P lyases, C–P hydrolases, and others of as-yet-uncharacterized mechanism. Expression of some of the pathways of phosphonate catabolism is controlled by ambient levels of inorganic P (Pi) but for others it is Pi-independent. In this report we review the enzymology of C–P bond metabolism in bacteria, and also present the results of an in silico investigation of the distribution of the genes that encode the pathways responsible, in both bacterial genomes and in marine metagenomic libraries, and their likely modes of regulation. Interrogation of currently available whole-genome bacterial sequences indicates that some 10% contain genes encoding putative pathways of phosphonate biosynthesis while ∼40% encode one or more pathways of phosphonate catabolism. Analysis of metagenomic data from the global ocean survey suggests that some 10 and 30%, respectively, of bacterial genomes across the sites sampled encode these pathways. Catabolic routes involving phosphonoacetate hydrolase, C–P lyase(s), and an uncharacterized 2-aminoethylphosphonate degradative sequence were predominant, and it is likely that both substrate-inducible and Pi-repressible mechanisms are involved in their regulation. The data we present indicate the likely importance of phosphonate-P in global biogeochemical P cycling, and by extension its role in marine productivity and in carbon and nitrogen dynamics in the oceans.

Studies on the biodegradation of fosfomycin: synthesis of 13C-labeled intermediates, feeding experiments with Rhizobium huakuii PMY1, and isolation of labeled amino acids from cell mass by HPLC

Racemic (1R*,2R*)-1,2-dihydroxy-[1-(13)C(1)]propylphosphonic acid and 1-hydroxy-[1-(13)C(1)]acetone were synthesized and fed to R. huakuii PMY1. Alanine and a mixture of valine and methionine were isolated as their N-acetyl derivatives from the cell hydrolysate by reversed-phase HPLC and analyzed by NMR spectroscopy. It was found that the carbon atoms of the respective carboxyl groups were highly (13)C-labeled (up to 65 %). Hydroxyacetone is therefore considered an obligatory intermediate of the biodegradation of fosfomycin by R. huakuii PMY1.

Direct quantification of inorganic polyphosphate in microbial cells using 4'-6-diamidino-2-phenylindole (DAPI)

Inorganic polyphosphate (polyP) is increasingly being recognized as an important phosphorus sink within the environment, playing a central role in phosphorus exchange and phosphogenesis. Yet despite the significant advances made in polyP research there is a lack of rapid and efficient analytical approaches for the quantification of polyP accumulation in microbial cultures and environmental samples. A major drawback is the need to extract polyP from cells prior to analysis. Due to extraction inefficiencies this can lead to an underestimation of both intracellular polyP levels and its environmental pool size: we observed 23-58% loss of polyP using standard solutions and current protocols. Here we report a direct fluorescence based DAPI assay system which removes the requirement for prior polyP extraction before quantification. This increased the efficiency of polyP detection by 28-55% in microbial cultures suggesting quantitative measurement of the intracellular polyP pool. It provides a direct polyP assay which combines quantification capability with technical simplicity. This is an important step forward in our ability to explore the role of polyP in cellular biology and biogeochemical nutrient cycling.