Photooxidative Damage in Photosynthetic Activities of Chromatium vinosum

Abstract

The capacity of photosynthetic CO2 fiXation in the anaerobic purplesulfur bacterium, COmadum vinosum is markedly impaired by strong ilumination (9 x 10i lux) in the presence of 100% 0s. In the absence of HCO0, decline in activity occurred gradually, with about 40% of the initial activity reminng after a 1-hour incubation. The addition of 50 milimolar HCOj-to the incubation medium resulted in a measurable delay (about 30 minutes) of the inactivation process. Ribulose-1,5-bisphosphate carboxylase activty and light-dependent Os uptake (electron flow) or crude extracts prepared after pretreatment of the bacterial cells with 02 and light were not affected but the photophosphorylation capacity of either bacterial cells or chromatophores was drastically reduced. The inhibition of photophosphorylation in the chromatophore preparations was signiflcantiy reduced by the addition of either an Os scavenger, Tiron, or an 102 scavenger, atocopherol. These results suggest that the active O2 species, Os2 or 10, might take part in the observed inactivation.The pretreatment of the bacteria with 02 and light inhibited CO2 assimilation through the Calvin-Benson cycle, while relatively stimulating the formation of aspartate and glutamate. It also inhibited the conversion of glycolate to glycine, resulting in a sustained extraceUlular excretion of glycolate. The inactivation of photosynthetic CO2 fixation by intact cells was enhanced by low temperature, KCN, or methylviologen addition during the pretreatment with 02 and light. The mechanism(s) of 02-dependent photoinactivation of photosynthetic activities in Chromadum are discussed in relation to the possible role of photorespiration as a means of producing CO2 in the photosynthetic system.There are two types of inhibitory effects of 02 on photosynthesis in various photoautotrophic organisms. The first mechanism which is reversible and is often referred to as the Warburg effect is considered to govern photorespiratory processes. It is likely a result of the competitive inhibition of CO2 fixation by 02 (14,15,20,34). We have previously demonstrated an inhibitory effect of 02 on photosynthetic CO2 fixation as well as the mechanism of glycolate biosynthesis and metabolism by the photosynthetic anaerobic bacterium, Chromatium vinosum, which are phenomenologically similar to the Warburg effect observed in higher plants (7,29). The second type of 02 inhibition, which is irreversible and often referred to as the photodynamic action, is caused by photooxidation damage of cellular component(s) (36). A number of isolated enzymes or photosystem(s) in green plants are subject to photooxidative inactivation (12,18,22,26,33). The Chl-bearing photosystems of photosynthetic organisms serve to transform ra-

Inhibition of phototrophically growing Chromatium vinosum D by glycine

“…While high metabolite turnover rates would be expected to result in a low glycine pool concentration [17] and tittle glycine efflux under natural growth conditions, consideration of certain aspects of CO 2 fixation by C. vinosum provides a rationale for the possible occurrence of glycine efflux in C. vinosum. CO2-fixation in C. vinosurn occurs via the Calvin cycle and involves ribulosebisphosphate carboxylase which, in the presence of oxygen, exhibits oxygenase activity [18] producing glycolate which is eventually converted to glycine [19,20]. Thus, the facultative chemotroph C. vinosum [21,22] may be expected to accumulate glycine during autotrophic growth in the dark under micro-to semiaerobic conditions.…”

Measurement of Photosynthesis Using PAM Technology in a Purple Sulfur Bacterium Thermochromatium tepidum (Chromatiaceae)

“…Thus, it would be expected that photosynthetic rates nearer to the optimum temperatures for this thermophile would be considerably above those measured in this study, probably by a factor of about 2–5. The other limitation of this study was that Thermochromatium is much more sensitive to oxygen and hence harder to grow than rhodopseudomonads. Thermochromatium would also be expected to be more adversely affected by oxygen when filtered onto glass fiber disks than Afifella and Rhodopseudomonas , hence the lower maximum yields shown in Fig.…”

“…Provision of an organic carbon source (acetate) because it is known that Chromatium has a limited capacity for aerobic metabolism of acetate did improve the yield ( Y ) but did not improve photosynthesis when Fe 2+ was provided as an electron source. Perhaps different results would have been found if it was possible to perform the PAM measurements under strict anoxic conditions because CO 2 fixation in Chromatium is known to be is strongly O 2 sensitive .…”

Photoinactivation of Microcystis aeruginosa ribulose 1,5-bisphosphate carboxylase: Effects of endogenous and added sensitizers and the role of oxygen

“…Direct effects of light on the activation of the enzyme have also been reported [2,3]. In contrast, visible light has also been implicated in a photoinactivation of RuBP carboxylase in cyanobacterial cells [4,5] and in extracts from purple sulfur bacteria, cyanobacteria, green algae and higher plants in the presence of a sensitizer [6][7][8][9]. The photoinactivation of RuBP carboxylase may occur during the frequently observed photoinhibiti0n of phytoplankton photosynthesis in natural waters [10].…”