Aquaporin AqpZ is involved in cell volume regulation and sensitivity to osmotic stress in Synechocystis sp. strain PCC 6803

Masaro Akai, Kiyoshi Onai, Megumi Morishita, Hiroyuki Mino, Toshiaki Shijuku, Hisataka Maruyama, Fumihito Arai, Shigeru Itoh, Akihiro Hazama, Vanessa Checchetto, Ildikò Szabò, Yoshinori Yukutake, Makoto Suematsu, Masato Yasui, Masahiro Ishiura, Nobuyuki Uozumia

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23 Citations (Scopus)


The moderately halotolerant cyanobacterium Synechocystis sp. strain PCC 6803 contains a plasma membrane aquaporin, AqpZ. We previously reported that AqpZ plays a role in glucose metabolism under photomixotrophic growth conditions, suggesting involvement of AqpZ in cytosolic osmolarity homeostasis. To further elucidate the physiological role of AqpZ, we have studied its gene expression profile and its function in Synechocystis. The expression level of aqpZ was regulated by the circadian clock. AqpZ activity was insensitive to mercury in Xenopus oocytes and in Synechocystis, indicating that the AqpZ can be categorized as a mercury-insensitive aquaporin. Stopped-flow light-scattering spectrophotometry showed that addition of sorbitol and NaCl led to a slower decrease in cell volume of the Synechocystis ΔaqpZ strain than the wild type. The ΔaqpZ cells were more tolerant to hyperosmotic shock by sorbitol than the wild type. Consistent with this, recovery of oxygen evolution after a hyperosmotic shock by sorbitol was faster in the ΔaqpZ strain than in the wild type. In contrast, NaCl stress had only a small effect on oxygen evolution. The amount of AqpZ protein remained unchanged by the addition of sorbitol but decreased after addition of NaCl. This decrease is likely to be a mechanism to alleviate the effects of high salinity on the cells. Our results indicate that Synechocystis AqpZ functions as a water transport system that responds to daily oscillations of intracellular osmolarity.

Original languageEnglish
Pages (from-to)6828-6836
Number of pages9
JournalJournal of Bacteriology
Issue number24
Publication statusPublished - 2012 Oct

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


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