Function of the N-terminal region of the phosphate-sensing histidine kinase, SphS, in Synechocystis sp. PCC 6803

Kimura, Satoshi; Shiraiwa, Yoshihiro; Suzuki, Iwane

doi:10.1099/mic.0.028514-0

Cited by 11 publications

(16 citation statements)

References 39 publications

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“…During P i limitation, the PhoR histidine kinase phosphorylates the PhoB response regulator, which in turn induces the transcription of the Pho regulon (5,26,27). PhoR does not directly respond to environmental P i levels (28,29); instead, it is believed that the activity of PhoR is regulated by a signal cascade involving PstSCAB and PhoU (5). It was hypothesized that PhoU detects the conformational state of PstSCAB and transmits this to PhoR (5).…”

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confidence: 99%

PhoU Allows Rapid Adaptation to High Phosphate Concentrations by Modulating PstSCAB Transport Rate in Sinorhizobium meliloti

et al. 2017

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Maintenance of cellular phosphate homeostasis is essential for cellular life. The PhoU protein has emerged as a key regulator of this process in bacteria, and it is suggested to modulate phosphate import by PstSCAB and control activation of the phosphate limitation response by the PhoR-PhoB two-component system. However, a proper understanding of PhoU has remained elusive due to numerous complications of mutating phoU, including loss of viability and the genetic instability of the mutants. Here, we developed two sets of strains of Sinorhizobium meliloti that overcame these limitations and allowed a more detailed and comprehensive analysis of the biological and molecular activities of PhoU. The data showed that phoU cannot be deleted in the presence of phosphate unless PstSCAB is inactivated also. However, phoU deletions were readily recovered in phosphatefree media, and characterization of these mutants revealed that addition of phosphate to the environment resulted in toxic levels of PstSCAB-mediated phosphate accumulation. Phosphate uptake experiments indicated that PhoU significantly decreased the PstSCAB transport rate specifically in phosphate-replete cells but not in phosphate-starved cells and that PhoU could rapidly respond to elevated environmental phosphate concentrations and decrease the PstSCAB transport rate. Sitedirected mutagenesis results suggested that the ability of PhoU to respond to phosphate levels was independent of the conformation of the PstSCAB transporter. Additionally, PhoU-PhoU and PhoU-PhoR interactions were detected using a bacterial two-hybrid screen. We propose that PhoU modulates PstSCAB and PhoR-PhoB in response to local, internal fluctuations in phosphate concentrations resulting from PstSCAB-mediated phosphate import.IMPORTANCE Correct maintenance of cellular phosphate homeostasis is critical in all kingdoms of life and in bacteria involves the PhoU protein. This work provides novel insights into the role of the Sinorhizobium meliloti PhoU protein, which plays a key role in rapid adaptation to elevated phosphate concentrations. It is shown that PhoU rapidly responds to elevated phosphate levels by significantly decreasing the phosphate transport of PstSCAB, thereby preventing phosphate toxicity and cell death. Additionally, a new model for phosphate sensing in bacterial species which involves the PhoR-PhoB two-component system is presented. This work provides new insights into the bacterial response to changing environmental conditions and into regulation of the phosphate limitation response that influences numerous bacterial processes, including antibiotic production and virulence.KEYWORDS Pho regulon, PhoU, PstSCAB, Sinorhizobium meliloti, environmental adaptation, modulation of TCS, phosphate homeostasis, phosphate sensing, phosphate transport, transport modulation

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confidence: 99%

PhoU Allows Rapid Adaptation to High Phosphate Concentrations by Modulating PstSCAB Transport Rate in Sinorhizobium meliloti

et al. 2017

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“…These conditions have routinely been used to investigate the Pho regulon in cyanobacteria [2,14,15]. Synechocystis 6803 cells are able to survive under Pi-limiting conditions following initial growth in BG-11 although photoautotrophic growth and pigment content decreased [3].…”

Section: Discussionmentioning

confidence: 99%

Na+-stimulated phosphate uptake system in Synechocystis sp. PCC 6803 with Pst1 as a main transporter

2011

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BackgroundMost living cells uptake phosphate, an indispensable nutrient for growth from their natural environment. In Synechocystis sp. PCC 6803, the cells lack phosphate-inorganic transport (Pit) system but contain two phosphate-specific transport (Pst) systems, Pst1 and Pst2. We investigated the kinetics of Pi uptake of these two Pst systems by constructing the two mutants, ΔPst1 and ΔPst2, and comparing their kinetic properties with those of the wild-type cells under both Pi-sufficient and deficient conditions. The effects of pH and Na+ on the uptake of phosphate in Synechocystis were also studied.ResultsGrowth rates of the two mutants and wild type were similar either under phosphate-sufficient or deficient condition. The Km for phosphate uptake was 6.09 μM in wild type and this was reduced to 0.13 μM in ΔPst1 cells and 5.16 μM in the ΔPst2 strain. The Vmax values of 2.48, 0.22, and 2.17 μmol • (min • mg of chlorophyll a)-1 were obtained for wild type, the ΔPst1 and ΔPst2 strains, respectively. A monophasic phosphate uptake was observed in wild-type cells. The uptake of phosphate was energy and pH-dependent with a broad pH optimum between pH 7-10. Osmolality imposed by NaCl stimulated phosphate uptake whereas that imposed by sorbitol decreased uptake, suggesting stimulation of uptake was dependent upon ionic effects.ConclusionThe data demonstrate that Pst2 system of Synechocystis has higher affinity toward phosphate with lower Vmax than Pst1 system. The Pst1 system had similar Km and Vmax values to those of the wild type suggesting that Pst1 is the main phosphate transporter in Synechocystis sp. PCC 6803. The Km of Pst1 of Synechocystis is closer to that of Pit system than to that of the Pst system of E. coli, suggesting that Synechocystis Pst1 is rather a medium/low affinity transporter whereas Pst2 is a high affinity transporter.

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“…8, Case 3). The longterm effects observed in these experiments suggest a new functional organisation of membrane proteins via Pho regulon expression (Juntarajumnong et al 2007, Burut-Archanai et al 2009, Kimura et al 2009). Changes in gene expression of phosphate binding proteins in Synechocystis (Pitt et al 2010) and Trichodesmium ) as well as membrane protein patterns in Synechococcus , Scanlan et al 1997 of Trichodesmium sp.…”

Section: Influence Of T R On Growth Optimisationmentioning

confidence: 91%

Rapid regulation of phosphate uptake in freshwater cyanobacterial blooms

Aubriot¹,

Bonilla²

2012

Aquat. Microb. Ecol.

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Cyanobacterial blooms are generally explained by nutrient uptake kinetic constants that may confer competitive capabilities, like high nutrient-uptake rate, affinity, and storage capacity. However, cyanobacteria are capable of flexible physiological responses to environmental nutrient fluctuations through adaptation of their phosphate uptake properties. Growth optimization is possible if the physiological reaction time of cyanobacteria (t R ) matches the duration of nutrient availability. Here, we investigate the t R of this complex physiological process. We performed [ 32 P] uptake experiments with filamentous cyanobacterial blooms. The phytoplankton were subjected to different nutrient exposure times (t E ) by varying patterns of phosphate additions. After 15 to 25 min of phosphate t E , the cyanobacteria-dominated phytoplankton began their adaptive response by reducing and finally ceasing uptake activity before exhausting their nutrient uptake capacity. The time of onset of phosphate uptake regulation (in min) is an indicator of t R . Rapid adaptive behaviour may be the initial phase of longer-term nutrient acclimation (hours to days), which results in a higher growth rate. The growth response of bloom-forming cyanobacteria may be more dependent on the ability to optimize the uptake of phosphate during the time span of nutrient fluctuation than on the amount of nutrient taken up per se. Freshwater cyanobacterial blooms may therefore be promoted by their short t R during phosphate fluctuations.

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Function of the N-terminal region of the phosphate-sensing histidine kinase, SphS, in Synechocystis sp. PCC 6803

Cited by 11 publications

References 39 publications

PhoU Allows Rapid Adaptation to High Phosphate Concentrations by Modulating PstSCAB Transport Rate in Sinorhizobium meliloti

PhoU Allows Rapid Adaptation to High Phosphate Concentrations by Modulating PstSCAB Transport Rate in Sinorhizobium meliloti

Na+-stimulated phosphate uptake system in Synechocystis sp. PCC 6803 with Pst1 as a main transporter

Rapid regulation of phosphate uptake in freshwater cyanobacterial blooms

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