Long-Term Response toward Inorganic Carbon Limitation in Wild Type and Glycolate Turnover Mutants of the Cyanobacterium Synechocystis sp. Strain PCC 6803

Abstract

Concerted changes in the transcriptional pattern and physiological traits that result from long-term (here defined as up to 24 h) limitation of inorganic carbon (C i ) have been investigated for the cyanobacterium Synechocystis sp. strain PCC 6803. Results from reverse transcription-polymerase chain reaction and genome-wide DNA microarray analyses indicated stable up-regulation of genes for inducible CO 2 and HCO 3 2 uptake systems and of the rfb cluster that encodes enzymes involved in outer cell wall polysaccharide synthesis. Coordinated up-regulation of photosystem I genes was further found and supported by a higher photosystem I content and activity under low C i (LC) conditions. Bacterial-type glycerate pathway genes were induced by LC conditions, in contrast to the genes for the plant-like photorespiratory C2 cycle. Down-regulation was observed for nitrate assimilation genes and surprisingly also for almost all carboxysomal proteins. However, for the latter the observed elongation of the half-life time of the large subunit of Rubisco protein may render compensation. Mutants defective in glycolate turnover (DglcD and DgcvT) showed some transcriptional changes under high C i conditions that are characteristic for LC conditions in wild-type cells, like a modest down-regulation of carboxysomal genes. Properties under LC conditions were comparable to LC wild type, including the strong response of genes encoding inducible high-affinity C i uptake systems. Electron microscopy revealed a conspicuous increase in number of carboxysomes per cell in mutant DglcD already under high C i conditions. These data indicate that an increased level of photorespiratory intermediates may affect carboxysomal components but does not intervene with the expression of majority of LC inducible genes.

Metabolic and Transcriptomic Phenotyping of Inorganic Carbon Acclimation in the Cyanobacterium Synechococcus elongatus PCC 7942

“…Genes coding for proteins involved in the active uptake of C i (bicarbonate and/or CO 2 ) as part of the CCM showed the highest increase in transcript levels 6 h after the LC shift, as was found previously by reverse transcription-PCR and northern-blot hybridization in Synechococcus species (Woodger et al, 2003(Woodger et al, , 2007 and in Synechocystis 6803 (Wang et al, 2004;Eisenhut et al, 2007). The strongest responses are found for the bicarbonate-specific ATP-binding cassette transporter BCT1 and the symporter SbtA (Table II).…”

“…3). These responses were found previously in Synechocystis 6803 under identical conditions (Eisenhut et al, 2007). Based on this data set, the initial dephosphorylation of 2PG seems to be a crucial, possibly rate-liming step after a shift to LC, whereas the subsequent glycolate metabolism with the three branches appears to be mostly constitutively expressed and coordinated toward efficient detoxification and avoidance of significant accumulation of photorespiratory intermediates.…”

“…However, these LC-induced transcript levels are clearly not controlled by the PII-based C-N sensor system, since the changes are similar in the wild type and the MP2 mutant (Table II). As found previously in Synechocystis 6803 (Eisenhut et al, 2007), genes for the carboxysomal proteins and Rubisco are not significantly increased 6 h after the LC shift, with the exception of carbonic anhydrase. However, ccmK, ccmM, and rbcL showed transient increases in mRNA levels when cells of Synechococcus 7942 were analyzed during the first 60 min after a shift to CO 2 -free air (Woodger et al, 2003).…”

“…To analyze the acclimation of Synechococcus 7942 to low C i , HC-acclimated cells (grown for several days under 5% CO 2 ) of the wild type and the PII mutant MP2 were shifted to LC conditions (grown under 0.035% CO 2 by bubbling with ambient air), and samples were taken for metabolome and transcriptome characterization after 6 and 24 h. Growth conditions and sampling parameters were essentially the same as used before in our experiments with Synechocystis 6803 (Eisenhut et al, 2007(Eisenhut et al, , 2008a to allow for comparison of the data sets. Under our culture conditions, wild-type cells grew better than the MP2 mutant (Fig.…”

“…PCC 6803 (hereafter referred to as Synechocystis 6803), was the most commonly studied strain because its genome sequence had been published in 1996 (Kaneko et al, 1996). Based on this genome sequence, DNA microarrays were generated, allowing the characterization of global transcriptional changes, including studies of HC/LC shifts or acclimation to different light conditions (Hihara et al, 2001;Wang et al, 2004;Eisenhut et al, 2007). Later, the genome sequences and respective "omics" tools of Synechococcus 7942, as well as those of the almost identical strain PCC 6301, became accessible (for Synechococcus 7942, see http:// www.ncbi.nlm.nih.gov/nuccore/NC_007604; for strain PCC 6301, see http:/ /genome.kazusa.or.jp/cyanobase/ PCC6301; Sugita et al, 2007;Nodop et al, 2008).…”