Plasma Membrane Aquaporin AqpZ Protein Is Essential for Glucose Metabolism during Photomixotrophic Growth of Synechocystis sp. PCC 6803

Abstract

The genome of Synechocystis PCC 6803 contains a single gene encoding an aquaporin, aqpZ. The AqpZ protein functioned as a water-permeable channel in the plasma membrane. However, the physiological importance of AqpZ in Synechocystis remains unclear. We found that growth in glucose-containing medium inhibited proper division of ⌬aqpZ cells and led to cell death. Deletion of a gene encoding a glucose transporter in the ⌬aqpZ background alleviated the glucose-mediated growth inhibition of the ⌬aqpZ cells. The ⌬aqpZ cells swelled more than the wild type after the addition of glucose, suggesting an increase in cytosolic osmolarity. This was accompanied by a down-regulation of the pentose phosphate pathway and concurrent glycogen accumulation. Metabolite profiling by GC/TOF-MS of wild-type and ⌬aqpZ cells revealed a relative decrease of intermediates of the tricarboxylic acid cycle and certain amino acids in the mutant. The changed levels of metabolites may have been the cause for the observed decrease in growth rate of the ⌬aqpZ cells along with decreased PSII activity at pH values ranging from 7.5 to 8.5. A mutant in sll1961, encoding a putative transcription factor, and a ⌬hik31 mutant, lacking a putative glucose-sensing kinase, both exhibited higher glucose sensitivity than the ⌬aqpZ cells. Examination of protein expression indicated that sll1961 functioned as a positive regulator of aqpZ gene expression but not as the only regulator. Overall, the ⌬aqpZ cells showed defects in macronutrient metabolism, pH homeostasis, and cell division under photomixotrophic conditions, consistent with an essential role of AqpZ in glucose metabolism.

Cyanobacteria produce arsenosugars

“…Synechocystis cells were grown axenically in sterilised BG-11 medium (nitrogen content, 18 mM; phosphorus content, 0.2 mM) [33] containing glucose (5 mM) with vigorous shaking at 120 rpm. [34] Nostoc cells were grown axenically in sterile BG-11 medium with orbital shaking, with or without air-bubbling. The cyanobacterial cells of each strain were incubated in 300 mL of medium in 500-mL Erlenmeyer flasks at 30 and 28 8C, with continuous illumination at 40 mmol photons m À2 s À1 .…”

Aquaporin AqpZ Is Involved in Cell Volume Regulation and Sensitivity to Osmotic Stress in Synechocystis sp. Strain PCC 6803

“…The AqpZ protein resides in the plasma membrane in the cell (1). Deletion of Synechocystis aquaporin aqpZ resulted in an increase in cell volume in the presence of low concentrations (5 mM) of glucose (1). This indicates that AqpZ plays a crucial role in the cellular osmotic adaptation to fluctuation of cytosolic osmotic pressure due to production and consumption of the photosynthetic products synthesized during the day.…”

“…A P dnaK :: luxAB bioluminescent reporter strain (4, 24) was used as a control. Cells were grown to colonies on solid BG11 medium (1,42) at 30°C under white fluorescence lamps (42 mol of photons m Ϫ2 s Ϫ1 ), placed in the dark for 12 h to synchronize the circadian clock, and then kept under constant light. Bioluminescence from colonies was measured automatically every hour as described previously (35,36) using automated bioluminescence monitoring apparatuses (K. Okamoto, K. Onai, and M. Ishiura, unpublished data; models LL04-1 and CL24-W; Churitsu Electric Corp., Nagoya, Japan).…”

“…Synechocystis contains in its genome a single-copy gene encoding an aquaporin homolog, aqpZ (1,7,42). The AqpZ protein resides in the plasma membrane in the cell (1). Deletion of Synechocystis aquaporin aqpZ resulted in an increase in cell volume in the presence of low concentrations (5 mM) of glucose (1).…”

“…Simultaneously with the transport of ions across the membrane or the change in intracellular concentration of compatible solutes, such as glucosylglycerol, carbamides, polyols, purines, pyrimidines, and glycerol, by de novo synthesis in response to the external salt concentration or osmolarity change, water flux occurs mainly through water-permeable channels called aquaporins (18,19,31,32,39,40,44,47). Synechocystis contains in its genome a single-copy gene encoding an aquaporin homolog, aqpZ (1,7,42). The AqpZ protein resides in the plasma membrane in the cell (1).…”