An Oxidative Pathway for Microbial Utilization of Methylphosphonic Acid as a Phosphate Source

Abstract

Methylphosphonic acid is synthesized by marine bacteria and is a prominent component of dissolved organic phosphorus. Consequently, methylphosphonic acid also serves as a source of inorganic phosphate (Pi) for marine bacteria that are starved of this nutrient. Conversion of methylphosphonic acid into Pi is currently only known to occur through the carbon−phosphorus lyase pathway, yielding methane as a byproduct. In this work, we describe an oxidative pathway for the catabolism of methylphosphonic acid in Gimesia maris DSM8797. G. maris can use methylphosphonic acid as Pi sources despite lacking a phn operon encoding a carbon−phosphorus lyase pathway. Instead, the genome contains a locus encoding homologues of the non-heme Fe(II) dependent oxygenases HF130PhnY* and HF130PhnZ, which were previously shown to convert 2-aminoethylphosphonic acid into glycine and Pi. GmPhnY* and GmPhnZ1 were produced in E. coli and purified for characterization in vitro. The substrate specificities of the enzymes were evaluated with a panel of synthetic phosphonates. Via 31 P NMR spectroscopy, it is demonstrated that the GmPhnY* converts methylphosphonic acid to hydroxymethylphosphonic acid, which in turn is oxidized by GmPhnZ1 to produce formic acid and Pi. In contrast, 2-aminoethylphosphonic acid is not a substrate for GmPhnY* and is therefore not a substrate for this pathway. These results thus reveal a new metabolic fate for methylphosphonic acid.

Methylphosphonate Oxidation in Prochlorococcus Strain MIT9301 Supports Phosphate Acquisition, Formate Excretion, and Carbon Assimilation into Purines

“…In this study, we found that Prochlorococcus strain MIT9301 can grow on MPn or HMPn as the sole source of P. Our data support the hypothesis that this capability is mediated by the putative phosphonate oxidative pathway encoded by the phnY and phnZ genes (16–18). Strain MED4, a high-light-adapted strain isolated from the oligotrophic and P i -depleted surface waters of the Mediterranean Sea (22), lacks these genes and is accordingly unable to utilize 2-AEP (20).…”

“…In this study, we present evidence that MIT9301 can utilize two previously unrecognized phosphonates enriched in marine HMW DOM, methylphosphonate (MPn) and hydroxymethylphosphonate (HMPn) (11). Our findings indicate that Prochlorococcus strain MIT9301 metabolizes these phosphonates to obtain P and can also excrete and assimilate the methyl group released during MPn and HMPn CP bond cleavage as formate, consistent with the MPn-specific oxidative mechanism identified in the marine planctomycete Gimesia maris (18). Our results support the hypothesis that phosphonates play an important role in the daily P nutrition of microbial communities in marine environments limited by P i and implicate the degradation of MPn and HMPn by Prochlorococcus as a potential source of formate for bacteria.…”

“…Most recently, phnY and phnZ homologs belonging to the marine planctomycete G. maris DSM8797 were expressed in E. coli and shown to confer the ability to specifically oxidize MPn to HMPn and subsequently to formate and P i (18). Based on sequence clustering, the phnY and phnZ genes in G. maris were predicted to be closely related to the Prochlorococcus phnY and phnZ genes (18).…”

“…There is also a group of phosphonate hydrolases, or phosphonatases, whose substrates contain an electron-withdrawing β-carbonyl group that facilitates bond cleavage (15). Most recently, CP bond cleavage systems that employ an oxidative pathway have been identified and characterized (16–18).…”

“…The Prochlorococcus high-light-adapted strain MIT9301 and low-light-adapted strain MIT9303 harbor two genes, phnY and phnZ , predicted to encode a phosphonate oxidative pathway (16–18) colocated with an ATP-binding cassette transporter system for phosphite and phosphonates (19) and with the P i response regulator phoB (7). Despite the presence of these genes in Prochlorococcus isolates, previous studies have failed to demonstrate Prochlorococcus utilization of phosphonates as the sole source of P (20).…”