25 μM and 20 μM, respectively [6]. In E. coli, the MLN8237 research buy high-affinity Pst system belongs to the Pho regulon and when environmental Pi is in excess (greater than 4 μM) the expression of genes of the Pho regulon is not induced [5]. Therefore under Pi-replete conditions Pi uptake occurs via the Pit system. Many cyanobacteria also exhibited different kinetic parameters for Pi uptake when grown under

Pi-limiting conditions than selleckchem when grown under Pi-replete conditions [7, 8]. For example, Synechococcus sp. PCC 7942 exhibits a lower K m for Pi uptake when grown under Pi-limiting conditions. This organism contains both low-affinity and high-affinity Pi transport systems where the high-affinity Pi transport activity is regulated by the periplasmic Pi-binding protein SphX [8]. In contrast, a low affinity Pit-like Pi transport system is thought to be absent in Synechocystis sp. PCC 6803 (hereafter Synechocystis 6803) [9]. This cyanobacterium was previously shown to contain two Pst systems, Pst1 and Pst2, that are up-regulated in response

to Pi limitation [4]. It is well known that the growth of cyanobacteria relies both on the size of the pool of internal polyphosphate and on their ability to take up Pi from the natural environment with fluctuating Pi levels [10, 11]. It is therefore of interest to investigate YH25448 in vitro the uptake of Pi by Pst1 and Pst2 of Synechocystis 6803. In this study we determined the kinetics of each Pst system using deletion mutants of each system in Synechocystis

6803. We demonstrated that Pst1 was the main Pi transporter whereas Pst2 might play a role in the uptake of Pi under low Pi environments. Results Growth of wild type and mutants The growth of wild-type Synechocystis 6803 was similar to that of the mutants lacking either Pst1 (ΔPst1 cells) or Pst2 (ΔPst2 cells) in BG-11 medium (Figure 1A). Under Pi-limiting conditions, the three strains also showed similar growth characteristics during the first two days but later on Non-specific serine/threonine protein kinase showed slightly slower growth rates than in BG-11 medium. The analysis of total Pi content of all three strains showed a small increase of total Pi during the first 24 h under Pi-replete conditions (Table 1). At 96 h, total Pi content decreased slightly or remained stable. On the other hand, under Pi-limiting conditions the three strains showed a decrease of total Pi at 24 h and only marginal contents were detected later in growth. In both situations, the total Pi content of the three strains was very similar at all time points tested. Figure 1 Photoautotrophic growth and absorption spectra of Synechocystis sp. PCC 6803 wild type, and the ΔPst1 and ΔPst2 mutants.