Aminophosphonate mineralisation is a major step in the global oceanic phosphorus redox cycle

Abstract

The planktonic synthesis of reduced organophosphorus molecules, such as alkylphosphonates and aminophosphonates, represents one half of a vast global oceanic phosphorus redox cycle. Whilst alkylphosphonates tend to accumulate in recalcitrant dissolved organic matter, aminophosphonates do not. Thus, we hypothesised unknown pathways for the uptake of aminophosphonates must exist in seawater. Here, we identify three novel bacterial 2-aminoethylphosphonate (2AEP) transporters, named AepXVW, AepP and AepSTU, whose expression is independent of phosphate concentrations (phosphate-insensitive). AepXVW, is found in diverse marine heterotrophs and is ubiquitously distributed in mesopelagic and epipelagic waters. Unlike the archetypal phosphate-regulated phosphonate binding protein, PhnD, the newly identified AepX is heavily transcribed (~100-fold>PhnD) in the global ocean independently of phosphate and nitrogen concentrations. Collectively, our data identifies a mechanism responsible for the oxidative step in the marine phosphorus redox cycle and suggests 2AEP may be an important source of regenerated phosphate, which is required for oceanic primary production.