title: Water and CO₂ permeability of SsAqpZ, the cyanobacterium Synechococcus sp. PCC7942 aquaporin.
abstract: BACKGROUND
  Cyanobacteria possess Aquaporin-Z (AqpZ) membrane channels which have been suggested to mediate the water efflux underlying osmostress-inducible gene expression and to be essential for glucose metabolism under photomixotrophic growth. However, preliminary observations suggest that the biophy-sical properties of transport and physiological meaning of AqpZ in such photosynthetic microorganisms are not yet completely assessed.
  
  
  RESULTS
  In this study, we used Xenopus laevis oocyte and proteoliposome systems to directly demonstrate the water permeability of the cyanobacterium Synechococcus sp. PCC7942 aquaporin, SsAqpZ. By an in vitro assay of intracellular acidification in yeast cells, SsAqpZ was found to transport also CO2 . Consistent with this result, during the entire exponential phase of growth, Synechococcus SsAqpZ-null-mutant cells grew slower than the corresponding wild-type cells. This phenotype was stronger with higher levels of extracellular CO2 . In line with the conversion of CO2 gas into HCO3(-) ions under alkaline conditions, the impairment in growth of the SsAqpZ-null strain was weaker in more alkaline culture medium.
  
  
  CONCLUSIONS
  Cyanobacterial SsAqpZ may exert a pleiotropic function in addition to the already reported roles in macronutrient homeostasis and osmotic-stress response as it appears to constitute an important pathway in CO2 uptake, a fundamental step in photosynthesis.
authors.affiliation: Graduate School of Bioresource Sciences, Akita Prefectural University, Shimoshinjo, Japan.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Ding
authors.forename: Tadashi
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Patrizia
authors.initials: P
authors.lastname: Gena
authors.forename: Chengwei
authors.initials: C
authors.lastname: Liu
authors.forename: Marialuisa
authors.initials: M
authors.lastname: Pellegrini-Calace
authors.forename: Shihua
authors.initials: S
authors.lastname: Zhong
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Sun
authors.forename: Yanming
authors.initials: Y
authors.lastname: Zhu
authors.forename: Maki
authors.initials: M
authors.lastname: Katsuhara
authors.forename: Ikuko
authors.initials: I
authors.lastname: Iwasaki
authors.forename: Yoshichika
authors.initials: Y
authors.lastname: Kitagawa
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Calamita
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000378:metabolism*; D001681:Biological Assay; D002245:Carbon Dioxide / Q000378:metabolism*; D002463:Cell Membrane Permeability; D008081:Liposomes / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000378:metabolism; D009995:Osmosis; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D046940:Synechococcus / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D014867:Water / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D020346:Aquaporins; D008081:Liposomes; D014867:Water; D002245:Carbon Dioxide