Succinate:Quinol Oxidoreductases in the Cyanobacterium Synechocystis sp. Strain PCC 6803: Presence and Function in Metabolism and Electron Transport

Abstract

The open reading frames sll1625 and sll0823, which have significant sequence similarity to genes coding for the FeS subunits of succinate dehydrogenase and fumarate reductase, were deleted singly and in combination in the cyanobacterium Synechocystis sp. strain PCC 6803. When the organic acid content in the ⌬sll1625 and ⌬sll0823 strains was analyzed, a 100-fold decrease in succinate and fumarate concentrations was observed relative to the wild type. A similar analysis for the ⌬sll1625 ⌬sll0823 strain revealed that 17% of the wild-type succinate levels remained, while only 1 to 2% of the wild-type fumarate levels were present. Addition of 2-oxoglutarate to the growth media of the double mutant strain prior to analysis of organic acids in cells caused succinate to accumulate. This indicates that succinate dehydrogenase activity had been blocked by the deletions and that 2-oxoglutarate can be converted to succinate in vivo in this organism, even though a traditional 2-oxoglutarate dehydrogenase is lacking. In addition, reduction of the thylakoid plastoquinone pool in darkness in the presence of KCN was up to fivefold slower in the mutants than in the wild type. Moreover, in vitro succinate dehydrogenase activity observed in wild-type membranes is absent from those isolated from the double mutant and reduced in those from the single mutants, further indicating that the sll1625 and sll0823 open reading frames encode subunits of succinate dehydrogenase complexes that are active in the thylakoid membrane of the cyanobacterium.

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

“…Furthermore, Nostoc PCC 73102 has no bidirectional hydrogenase activity at all but respires with rates comparable to those of other cyanobacteria (22). This could mean that cyanobacterial respiration partly circumvents respiratory complex I and utilizes the succinate dehydrogenase complex instead, as may be inferred from studies with mutants (49). Then the fate of the NAD(P)H generated in carbon catabolism has to be determined.…”

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

“…Another possible explanation for the coordinated increase of 2OG and succinate is to assume the existence of a modified rather than open TCA cycle. Experimental work on Synechocystis 6803 (Cooley et al, 2000) and a metabolic network model for this cyanobacterial strain (Knoop et al, 2010) suggest that a shunt exists that closes the TCA cycle, which starts from 2OG, goes over Glu, 4-aminobutanoate, succinate-semialdehyde, and goes back to succinate. Regardless of whether the TCA cycle is open or somehow closed, the newly fixed organic C is accumulated throughout the path from 3PGA via 2PGA to PEP and subsequently into intermediates of the TCA cycle.…”

Transcriptional Regulation of the Respiratory Genes in the CyanobacteriumSynechocystissp. PCC 6803 during the Early Response to Glucose Feeding

“…To detect a Glc-induced increase in respiratory electron flow, we indirectly measured the redox state of the PQ pool in thylakoids by monitoring the chlorophyll (Chl) a fluorescence yield in darkness (Cooley et al, 2000;Cooley and Vermaas, 2001). As shown in Figure 6C, treatment of Synechocystis cells with the respiratory electron transport inhibitors KCN and 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB) caused the F o level to increase in a sigmoid manner, reaching a maximal level after 8 min with a half-life of 3.9 min.…”

“…Cell density and Chl a content were determined using a UV-VIS spectrophotometer (Myers et al, 1980 Measurements of NAD(P)H (Ryu et al, 2003), Chl a, and AY fluorescence (Teuber et al, 2001;Ryu et al, 2004) from intact cells were performed as described previously. Reduction of the PQ pool was measured after 2 min of dark adaptation using a pulse amplitude modulation fluorometer (Walz) as described previously (Cooley et al, 2000;Cooley and Vermaas, 2001) with a slight modification. The increase in the fluorescence amplitude induced by weak measuring light (F o ) over time was followed for 1 min after the addition of 1 mM KCN, 50 mM DBMIB, and 5 mM sodium ascorbate.…”