Phosphate limitation threshold for phosphonate utilization and methane production by carbon–phosphorus lyase in Stutzerimonas frequens

Abstract The surface ocean is an important source of methane to the atmosphere, contributing 4% of natural global production. The degradation of methylphosphonate (MPn) is a key methane production pathway in the aerobic euphotic zone. Methylphosphonate is an important component of dissolved organic phosphorus (DOP), and it serves as a source of phosphorus (P) for microorganisms in oligotrophic regions of the ocean. Methylphosphonate is metabolized by bacteria into labile phosphorus and methane by the C‐P lyase enzymatic pathway. This pathway is regulated by the concentration of ambient inorganic phosphate (Pi) and is utilized to access alternative forms of P when bacteria experience P limitation. However, the concentration threshold of Pi, as it relates to the onset of C‐P lyase activity, is unknown. In this study, an isolate of the methane‐producing marine bacterium Stutzerimonas frequens (Pseudomonadaceae) was cultured under a range of Pi concentrations in the presence of MPn. In treatments where the estimated Pi concentration dropped below 92 nM, methane production was observed. Isotopic mass balance confirmed the methane was derived from MPn. The drawdown of MPn and the production of methane occurred concomitantly with the uptake of other organic P compounds, demonstrating that C‐P lyase is utilized in conjunction with other P acquisition pathways to combat Pi limitation. As the global climate shifts and increased warming strengthens stratification, increased P limitation may lead to higher rates of MPn utilization and methane production in the euphotic open ocean.