Quantum yields for oxygenic and anoxygenic photosynthesis in the cyanobacterium Oscillatoria limnetica

Abstract

A comparison of the quantum yield spectra of the oxygenic (H20 as the electron donor) with the anoxygenic (H2S as the electron donor) photosynthesis of the cyanobacterium, Oscillatoria limnetica reveals that anoxygenic photosynthesis is driven by photosystem I only. The highest quantum yields of the latter (maximum; 0.059 CO2 molecules/quantum of absorbed light) were obtained with wavelengths which preferentially excite photosystem I (<550, >650) in which chlorophyll a and-carotenoids are the major pigments. The addition of 3(3,4-dichlorophenyl)1,1-dimethylurea had no effect on anoxygenic photosynthesis, and no enhancement in quantum efficiency was observed by a superimposition of light preferentially exciting photosystem II.Oxygenic photosynthesis efficiently utilizes only a narrow range of the absorption spectrum (550-650 nm) where light is provided in excess to photosystem II via-phycocyanin. The quantum yield (0.033 CO2 molecules/quantum of absorbed light) is lower than the theoretical yield by a factor of 3, possibly due to inefficient light transfer from photosystem II to L. Thus, 3-fold enhancement of oxygenic photosynthesis by superimposition of photosystem I light, andlow quantum yields for anoxygenic photosynthesis, were obtained in this region. These results are consonant with the suggestion that such a cyanobacterium represents an intermediate stage in phototrophic evolution. The photosynthetic apparatus of the cyanobacteria ("blue-green algae") resembles that of eukaryotic algae and higher plants; it includes two photosystems, both utilizing water as the electron donor with the evolution of oxygen. Nevertheless, a number of cyanobacteria have been recently found which, in addition, display bacterial-type anoxygenic photosynthesis, driven by photosystem I with sulfide as the electron donor (1, 2). Thus, when the electron flow between photosystems II and I is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (Cl2Ph2Me2U), or when only photosystem I is excited by illumination with 703-nm light, anoxygenic photosynthesis proceeds with sulfide as the electron donor. Furthermore, two strains, Oscillatoria limnetica and Aphanothece halophytica have been shown to readily shift from aerobic growth with oxygenic photosynthesis to anaerobic growth and anoxygenic photosynthesis. In the anoxygenic photosynthesis of these strains, two sulfide molecules are oxidized to elemental sulfur for each CO2 molecule photoassimilated. The sulfur is then excreted from the cells (3).The ancient age since cyanobacteria appeared on earth (4) as well as a combination of prokaryotic cellular organization and oxygenic photosynthesis, underly the suggestion that cyanobacteria represent a primitive group of organisms from which the oxygenic plant-type photosynthesis evolved (5). The fact that various cyanobacteria (1, 2) display both anoxygenic and oxygenic photosynthesis and can readily shift from one to the other, points to the possibility that this faculty represents the missing link between bacterial type and plant t...

Oxygenic primary production below the oxycline and its importance for redox dynamics

“…Since we did not correct for the absorbance of light by particles other than phototrophic organisms, our calculated estimate represents a lower limit of quantum efficiency. Still, our values agree well with the values reported in other studies for cyanobacteria in the laboratory (0.03 mol E -1 , Oren et al 1977) and algae in the field (0.003-0.052 mol E -1 , Fahnenstiel et al 1984;Kirk 1994). Since we performed the in-situ incubations under very low light conditions in Lake Rot, we only obtained the initial, linear part of the P-I relation (Fig.…”

Na-Dithionite Promotes Photosynthetic Sulfide Utilization by the Cyanobacterium Oscillatoria limnetica

“…It photosynthetic electron transport chain at a site preceding PSI, and that both sulfide-dependent reactions, namely CO2 photoassimilation and H2 evolution, share a common electron transfer pathway at least up to Fd (5). Unlike many sulfide-oxidizing photosynthetic bacteria (19), 0. limnetica could not be shown to utilize other reduced sulfur compounds such as dithionite, thiosulfate, or sulfite for photoassimilation of CO2 (13). With the exception of several reports on very inefficient thiosulfate utilization by Anacystis nidulans (18,22), this observation seems to be true for all cyanobacterial strains tested, including those which share with 0. limnetica the ability to oxidize sulfide (see Ref.…”

“…Oscillatoria limnetica (7) was aerobically grown as previously described (15 (0), No additions or Na2S and 20 mm DBMIB; (A), Na2S; (M), Nadithionite; (0), Na2S and Na-dithionite; (V), Na2S, Na-dithionite, and 0.1 mM TMPD; (*), Na2S added following a 2-h preincubation in the light with Na-dithionite.…”

“…The bottles were then opened and the pH of the reaction mixture determined. The CO2 fixed was assayed in 1 ml of the cell suspension as previously described (15).…”

Sulfide induction of synthesis of a periplasmic protein in the cyanobacterium Oscillatoria limnetica

“…The insensitivity of anoxygenic photosynthesis to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and the absence of the red-drop phenomenon demonstrate that photosystem I alone is involved (7,12). Detailed electron transport inhibitor studies indicate that the sulfide electron donation site is at or just before the cytochrome b6 f complex (2)(3)(4)15).…”