Open AccessIdentification of an ATP-binding cassette transporter involved in bicarbonate uptake in the cyanobacterium Synechococcus sp. strain PCC 7942
Author(s) -
Tatsuo Omata,
G. Dean Price,
Murray R. Badger,
Masato Okamura,
Satoshi Gohta,
Teruo Ogawa
Publication year - 1999
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.96.23.13571
Subject(s) - operon , transporter , atp binding cassette transporter , synechococcus , cyanobacteria , bicarbonate , biochemistry , mutant , transcription (linguistics) , nitrate , biology , microbiology and biotechnology , chemistry , gene expression , gene , bacteria , ecology , linguistics , genetics , philosophy , endocrinology
Exposure of cells of cyanobacteria (blue–green algae) grown under high-CO2 conditions to inorganic C-limitation induces transcription of particular genes and expression of high-affinity CO2 and HCO3 − transport systems. Among the low-CO2 -inducible transcription units ofSynechococcus sp. strain PCC 7942 is thecmpABCD operon, encoding an ATP-binding cassette transporter similar to the nitrate/nitrite transporter of the same cyanobacterium. A nitrogen-regulated promoter was used to selectively induce expression of thecmpABCD genes by growth of transgenic cells on nitrate under high CO2 conditions. Measurements of the initial rate of HCO3 − uptake after onset of light, and of the steady-state rate of HCO3 − uptake in the light, showed that the controlled induction of thecmp genes resulted in selective expression of high-affinity HCO3 − transport activity. The forced expression ofcmpABCD did not significantly increase the CO2 uptake capabilities of the cells. These findings demonstrated that thecmpABCD genes encode a high-affinity HCO3 − transporter. A deletion mutant ofcmpAB (M42) retained low CO2 -inducible activity of HCO3 − transport, indicating the occurrence of HCO3 − transporter(s) distinct from the one encoded bycmpABCD . HCO3 − uptake by low-CO2 -induced M42 cells showed lower affinity for external HCO3 − than for wild-type cells under the same conditions, showing that the HCO3 − transporter encoded bycmpABCD has the highest affinity for HCO3 − among the HCO3 − transporters present in the cyanobacterium. This appears to be the first unambiguous identification and description of a primary active HCO3 − transporter.