Polyphosphate-kinase-1 dependent polyphosphate hyperaccumulation for acclimation to nutrient loss in the cyanobacterium, sp. PCC 6803.

Polyphosphate is prevalent in living organisms. To obtain insights into polyphosphate synthesis and its physiological significance in cyanobacteria, we characterize , a homolog of the polyphosphate-kinase-1 gene, in the freshwater cyanobacterium sp. PCC 6803. The Sll0290 protein structure reveals characteristics of Ppk1. A disruptant and -overexpressing transformant demonstrated loss and gain of polyphosphate synthesis ability, respectively. Accordingly, is identified as . The disruptant (Δ) grows normally with aeration of ordinary air (0.04% CO), consistent with its photosynthesis comparable to the wild type level, which contrasts with a previously reported high-CO (5%) requirement for Δ in an alkaline hot spring cyanobacterium, OS-B'. Δ is defective in polyphosphate hyperaccumulation and survival competence at the stationary phase, and also under sulfur-starvation conditions, implying that sulfur limitation is one of the triggers to induce polyphosphate hyperaccumulation in stationary cells. Furthermore, Δ is defective in the enhancement of total phosphorus contents under sulfur-starvation conditions, a phenomenon that is only partially explained by polyphosphate hyperaccumulation. This study therefore demonstrates that in , is not essential for low-CO acclimation but plays a crucial role in dynamic P-metabolic regulation, including polyP hyperaccumulation, to maintain physiological fitness under sulfur-starvation conditions.