Influence of organophosphonates as alternative P-sources on bacterial transformation of glyphosate

Glyphosate biotransformation under phosphorus (P)-limiting conditions has been demonstrated for numerous bacterial strains. However, besides glyphosate bacteria can utilize a broad spectrum of other biogenic and synthetic organophosphorus compounds (e.g., organophosphonates, OPs) as P-source. The ubiquity of OPs in the environment reduces the likelihood that bacteria will encounter conditions where glyphosate is the only P-containing compound. To study the impact of co-existing OPs on the biotransformation of glyphosate, we conducted batch cultivation experiments with the bacterial strains Achromobacter insolitus Kg 19 (A. Kg 19) and Ochrobactrum pituitosum GPr1-13 (O. GPr1-13) in which glyphosate and an additional OP were simultaneously provided as P-sources. Experiments with glyphosate and one additional monophosphonate (aminomethylphosphonate (AMPA), 2-aminoethylphosphonate (AEP), or phenylphosphonate (PPA)) showed that glyphosate was the least preferred P-source. Furthermore, the repeated supply of excess AMPA or AEP hindered the biotransformation of glyphosate. For strain A. Kg 19, AEP and AMPA threshold concentrations above which no glyphosate transformation occurred were approximately 40 and 120 μM, respectively. Conversely, in the presence of a synthetic diphosphonate (iminodi(methylene phosphonate) (IDMP) or 1-hydroxyethane 1,1-diphosphonate (HEDP)), strain A. Kg 19 preferred glyphosate as P-source. While IDMP was transformed after the depletion of glyphosate, HEDP concentration remained constant throughout the experiment and its presence retarded both cell growth and transformation of glyphosate. In light of the ubiquitous presence of AMPA and other OPs in the environment, our findings indicate that the presence of OPs may compromise the biotransformation potential of glyphosate, leading to lower transformation rates than those reported in previous studies.