Involved in the degradation of phospho-AI-2, thereby terminating induction of the lsr operon and closing the AI-2 signaling cycle. Catalyzes the conversion of (4S)-4-hydroxy-5-phosphonooxypentane-2,3-dione (P-DPD) to 3-hydroxy-5-phosphonooxypentane-2,4-dione (P-HPD)