A strain of Synechocystis sp. PCC 6803 without photosynthetic oxygen evolution and respiratory oxygen consumption: implications for the study of cyclic photosynthetic electron transport

Abstract

Cyclic electron transport around photosystem (PS) I is believed to play a role in generation of ATP required for adaptation to stress in cyanobacteria and plants. However, elucidation of the pathway(s) of cyclic electron flow is difficult because of low rates of this electron flow relative to those of linear photosynthetic and respiratory electron transport. We have constructed a strain of Synechocystis sp. PCC 6803 that lacks both PSII and respiratory oxidases and that, consequently, neither evolves nor consumes oxygen. However, this strain is still capable of cyclic electron flow around PSI. The photoheterotrophic growth rate of this strain increased with light intensity up to an intensity of about 25 mumol photons m-2 s-1, supporting the notion that cyclic electron flow contributes to ATP generation in this strain. Indeed, the ATP-generating ability of PSI is demonstrated by the fact that the PSII-less oxidase-less strain is able to grow at much higher salt concentrations than a strain lacking PSI. A quinone electrode was used to measure the redox state of the plastoquinone pool in vivo in the various strains used in this study. In contrast to what is observed in chloroplasts, the plastoquinone pool was rather reduced in darkness and was oxidized in the light. This is in line with significant electron donation by respiratory pathways (NADPH dehydrogenase and particularly succinate dehydrogenase) in darkness. In the light, the pool becomes oxidized due to the presence of much more PSI than PSII. In the oxidase-less strains, the plastoquinone pool was very much reduced in darkness and was oxidized in the light by PSI. Photosystem II activity did not greatly alter the redox state of the plastoquinone pool. The results suggest that cyclic electron flow around PSI can contribute to generation of ATP, and a strain deficient in linear electron transport pathways provides an excellent model for further investigations of cyclic electron flow.

Distinguishing the roles of thylakoid respiratory terminal oxidases in the cyanobacterium Synechocystis sp. PCC 6803

“…7). The FR lightmediated decrease of fluorescence suggested a highly reduced PQ pool in Δcox/cyd cells in darkness, which is in agreement with an earlier study by Howitt et al (2001). When a saturating pulse was applied over an FR light background, all strains demonstrated an increased maximum fluorescence level ( Fig.…”

Light Modulates the Biosynthesis and Organization of Cyanobacterial Carbon Fixation Machinery through Photosynthetic Electron Flow

“…6). Nontreated cells present similar clustering organization of carboxysomes as DCMU-treated cells, indicating that the PQ pool is oxidized upon the illumination condition, which possibly triggers the state transition to "State 1" (Mullineaux and Allen, 1990) or probably due to the high ratio of photosystem I and photosystem II in cyanobacteria (Howitt et al, 2001). Our results further reveal that the reorganization of carboxysomes appears as a long-term regulation process.…”

Succinate Dehydrogenase and Other Respiratory Pathways in Thylakoid Membranes of Synechocystis sp. Strain PCC 6803: Capacity Comparisons and Physiological Function

“…This apparatus has been used with plant mitochondria (6), pea chloroplasts (4), Rhodobacter membranes (28), and most recently with intact cells of Synechocystis sp. strain PCC 6803 (10). In PSI-containing strains, the PQ pool was fairly reduced in darkness and became increasingly oxidized at increasing light intensities ( Table 1).…”