Rapid phosphate uptake via an ABC transporter induced by sulfate deficiency in Synechocystis sp. PCC 6803

Abstract

Transport systems, which perform a pivotal function in regulating the import and export of various substances via cellular membranes, are important machinery in all living organisms. The ATP-binding cassette (ABC) transporter, one of such transporters, has a crucial role in the high-affinity uptake of various nutrients in bacteria. In the cyanobacterium Synechocystis sp. PCC 6803, a model cyanobacterium, its response to phosphate (Pi)-depleted conditions and the consequential regulation of the Pi transport system have been well-studied. However, its responses and the Pi uptake under Pi-repleted conditions are not comprehended yet. This study observed the peculiar stimulation of the Pi uptake following severe chlorosis in the Synechocystis cells grown under Pi-repleted conditions. The Synechocystis cells grown under high Pi conditions (approximately 4 mM) showed the rapid Pi uptake after 3 d of cultivation, and significantly severe degradation of chlorophyll was observed. Remarkably, the Synechocystis cells showed more than 16-fold higher Pi uptake at that time. Furthermore, we revealed that sulfate (S) deficiency-induced Pi uptake and that magnesium deficiency caused chlorosis and released the intracellularly accumulated Pi. Moreover, reverse genetics revealed that the rapid Pi uptake occurred via an ABC transporter induced by S deficiency, namely, a putative sulfate transporter, SbpA-CysTWA. Our findings provide a new perspective on the Pi uptake under high Pi conditions in cyanobacteria and bacteria.