Genes Essential to Sodium-dependent Bicarbonate Transport in Cyanobacteria

Abstract

The cyanobacterium Synechocystis sp. strain PCC 6803 possesses two CO 2 uptake systems and two HCO 3 ؊ transporters. We transformed a mutant impaired in CO 2 uptake and in cmpA-D encoding a HCO 3 ؊ transporter with a transposon inactivation library, and we recovered mutants unable to take up HCO 3 ؊ and grow in low CO 2 at pH 9.0. They are all tagged within slr1512 (designated sbtA). We show that SbtA-mediated transport is induced by low CO 2 , requires Na ؉ , and plays the major role in HCO 3 ؊ uptake in Synechocystis. Inactivation of slr1509 (homologous to ntpJ encoding a Na ؉ /K ؉ -translocating protein) abolished the ability of cells to grow at [Na ؉ ] higher than 100 mM and severely depressed the activity of the SbtA-mediated HCO 3 ؊ transport. We propose that the SbtA-mediated HCO 3 ؊ transport is driven by ⌬Na ؉ across the plasma membrane, which is disrupted by inactivating ntpJ. Phylogenetic analyses indicated that two types of sbtA exist in various cyanobacterial strains, all of which possess ntpJ. The sbtA gene is the first one identified as essential to Na ؉ -dependent HCO 3 ؊ transport in photosynthetic organisms and may play a crucial role in carbon acquisition when CO 2 supply is limited, or in Prochlorococcus strains that do not possess CO 2 uptake systems or Cmp-dependent HCO 3 ؊ transport.Growth of many photosynthetic microorganisms depends on the activity of a CO 2 -concentrating mechanism (CCM), 1 which raises the [CO 2 ] in close proximity to ribulose-1,5-bisphosphate carboxylase/oxygenase and thereby enables efficient CO 2 fixation despite the low affinity of the enzyme for CO 2 (1, 2). In the cyanobacterium Synechocystis sp. strain PCC 6803 (hereafter Synechocystis 6803), the CCM involves active CO 2 uptake and HCO 3 Ϫ transport. We have recently identified two systems for CO 2 uptake in Synechocystis 6803, one constitutive and the other inducible by low CO 2 (3). As deduced from phylogenetic analysis of proteins encoded by the genes involved, these CO 2 uptake systems are present in various cyanobacteria with the exception of Prochlorococcus marinus (3). The inducible system that depends on NdhD3/ NdhF3/CupA shows higher maximal activity and higher affinity for CO 2 than the constitutive, NdhD4/NdhF4/CupB-dependent system. Inactivation of two different genes, one encoding a component of the constitutive system and the other a constituent of the inducible system, abolished CO 2 uptake activity. The double mutants were unable to grow at pH 7.0 under air level of CO 2 (3, 4). In contrast, because the mutants possessed HCO 3 Ϫ transport capability, they could grow like the wild type (WT) at pH 9.0 in air.An ABC-type HCO 3 Ϫ transporter encoded by cmpABCD has been identified in Synechococcus sp. strain PCC 7942 (thereafter Synechococcus 7942) (5). Inactivation of cmp genes in Synechocystis 6803, however, had little effect on the HCO 3 Ϫ transport activity. This indicated that another HCO 3 Ϫ transporter, as yet unidentified, plays a central role in HCO 3 Ϫ uptake. Sodium ions are essential for ...

Genetic diversity of inorganic carbon uptake systems causes variation in CO2 response of the cyanobacterium Microcystis

“…Hence, to our knowledge, Microcystis is the first example of a cyanobacterium in which bicA and sbtA are located on the same operon. The presence of a sodium/proton antiporter gene on the same operon strengthens the hypothesis (Shibata et al, 2002;Price et al, 2004) that bicarbonate transport by BicA and SbtA is sodium-dependent. The presence of an upstream LysR-type transcriptional regulator gene, ccmR2, makes it likely that transcription of the bicA-sbtAB-nhaS3 operon is strongly regulated and dependent on environmental conditions.…”

“…So far, five different C i uptake systems have been identified in cyanobacteria, two for CO 2 and three for bicarbonate (Omata et al, 1999;Shibata et al, 2002;Price et al, 2004;Price, 2011). These uptake systems have different properties (Price et al, 2004), and not all uptake systems are present in every cyanobacterium (Rae et al, 2011).…”

“…The function of SbtB is still unknown, and it does not seem essential for SbtA activity (Price, 2011). Both SbtA and BicA are sodium-dependent bicarbonate transporters (Shibata et al, 2002;Price et al, 2004), although the molecular details of their sodium co-transport have not yet been elucidated . The third bicarbonate transporter, BCT1, has a medium substrate affinity (K 0.5 ¼ 10-15 mM bicarbonate) and low flux rate .…”

Anaerobic fermentation of glycerol byEscherichia coli: A new platform for metabolic engineering

“…Therefore, while CO 2 can freely diffuse in and out of the cell, HCO 3 À is a membrane-impermeable molecule. Although bicarbonate transport proteins have been identified in mammalian cells (Sterling and Casey, 2002) and cyanobacteria (Shibata et al, 2002), no such transporters have been reported in E. coli. While the principal reactions consuming bicarbonate/CO 2 in E. coli do so in the form of bicarbonate (whose only source is the hydration of CO 2 ), the reactions producing bicarbonate/CO 2 do so in the form of CO 2 .…”

Utilization of inorganic carbon in the edible cyanobacterium Ge‐Xian‐Mi (Nostoc) and its role in alleviating photo‐inhibition

“…1998;Omata et al . 1999;Shibata et al . 2002) and two CO 2 uptake systems associated with the operation of specialized NAD(P)H dehydrogenase complexes [one low-CO 2 inducible, dependent on NdhD3/NdhF3/CupA(ChpY); one constitutive, dependent on NdhD4/NdhF4/CupB(ChpX)] (Sültemeyer et al .…”