Anoxygenic Photosynthesis Research Articles

Solar Lake (Sinai). 2. Distribution of photosynthetic microorganisms and primary production1

The seasonal and vertical distributions of sulfur photosynthetic bacteria and cyanobacteria in Solar Lake, and their contribution to primary production, are described. During stratification, separate plates of the phototrophic sulfur bacteria Chromatium violescens and Prosthecochloris sp. develop. A bottom cyanobacterial bloom consisting of Oscillatoria spp. and Microcoleus sp. develops H2Sconcentrations up to 39 ppm and under light conditions down to 0.5% of surface light. The occurrence of a cyanobacterial bloom in the hypolimnion is explained by the facultative anoxygenic photosynthesis of Oscillatoria limnetica. Primary production is extremely high during stratification and reaches a maximum of 8,015 mg C m−2 d−1, 91% of which is produced in the metalimnion and hypolimnion. The overall annual production (59.09 g C m−2 yr−1) is low, owing to extremely low primary production in the epilimnion throughout stratification and in the whole column during holomixis. Stagnant conditions in a shallow body of water exposed to high irradiation leads to an inverse productivity profile.

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

A comparison of the quantum yield spectra of the oxygenic (H(2)O as the electron donor) with the anoxygenic (H(2)S 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 CO(2) 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 CO(2) 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 I. Thus, 3-fold enhancement of oxygenic photosynthesis by superimposition of photosystem I light, and low 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 position of cyanobacteria in the world of phototrophs

Recent advances in our knowledge of the biological properties of the cyanobacteria (former «blue-green algae») are reviewed. The subjects discussed include: cyanobacterial cell structure and development; comparative aspects of photosyntetic structure and function in prokaryotes; carbon metabolism and its relation to obligate photoautotrophy; and special properties of cyanobacteria that are of ecological significance (temperature relationships, nitrogen fixation and facultative anoxygenic photosynthesis).

Occurrence of facultative anoxygenic photosynthesis among filamentous and unicellular cyanobacteria

Eleven of 21 cyanobacteria strains examined are capable of facultative anoxygenic photosynthesis, as shown by their ability to photoassimilate CO2 in the presence of Na2S, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 703-nm light. These include different cyanobacterial types (filamentous and unicellular) of different growth histories (aerobic, anaerobic, and marine and freshwater). Oscillatoria limnetica, Aphanothece halophytica (7418), and Lyngbya (7104) have different optimal concentrations of Na2S permitting CO2 photoassimilation, above which the rate decreases: 3.5, 0.7, and 0.1 mM, respectively. In A. halophytica, for each CO2 molecule photoassimilated two sulfide molecules are oxidized to elemental sulfur, which is excreted from the cells. The ecological and evolutionary significance of anoxygenic photosynthesis in the cyanobacteria is discussed.

Sulphide-dependent anoxygenic photosynthesis in the cyanobacterium Oscillatoria limnetica

PROFOUND differences in structure and function separate the prokaryotic cyanobacteria (blue-green algae) from eukaryotic algae and plants, whereas oxygenic photosynthesis is considered to distinguish the cyanobacteria and eukaryotic plants from the other phototrophic bacteria. The prevailing concepts on the cyanobacteria emphasise their prokaryotic nature and oxygenic photosynthesis. This combination of properties, among others, led to the suggestion that the cyanobacteria represent a group of possible progenitors of chloroplasts1. While cyanobacteria typically exhibit oxygenic photosynthesis with two photosystems using electrons from water, it has been demonstrated that photosystem I of certain cyanobacteria can function in vivo independently in supporting virus production2, heterocyst functions3 and even photoheterotrophic growth4. We have demonstrated anoxygenic photosynthesis in a cyanobacterium Oscillatoria limnetica, also capable of oxygenic photosynthesis, which was isolated from the anaerobic H2S rich hypolimnion layer of the monomictic, hypersaline Solar Lake located on the desert margin of the Gulf of Elat, Israel5. During winter stratification, this layer is located below two plates of phototrophic sulphur bacteria (Chromatium violescens and Prosthecochloris sp.), and exhibits a dense cyanobacterial bloom with very high rates of primary production. We report here evidence for the photosystem I-driven CO2 photoassimilation in O. limnetica with H2S serving as sole electron donor through oxidation to elemental sulphur.

Facultative anoxygenic photosynthesis in the cyanobacterium Oscillatoria limnetica.

An isolate from H2S-rich layers of the Solar Lake, the cyanobacterium Oscillatoria limnetica, exhibits both oxygenic and anoxygenic photosynthesis. It can use Na2S as an electron donor for CO2 photoassimilation (photosystem I supplies the energy) in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea or 700-nm light. A stoichiometric ratio of approximately 2 is observed between the Na2S consumed and the photoassimilated CO2. The anoxygenic phototrophic capability of this cyanobacterium explains its growth in nature in high sulfide concentrations and indicates a selective advantage.

Observations on photosynthesis and related systems. I. Influence of anaerobiosis on photosynthetic rates during continuous irradiation

The extremely sensitive method of oxygen determination by the quenching of phosphorescence and the technique for the study of anaerobic photosynthesis used previously by Franck et al. has been modified and improved to the point where it has been possible to establish a known anaerobic state of 10 −6 mm. Hg of oxygen within 10 min. During photosynthesis at saturation, the concentration of oxygen in the sample (expressed in terms of the pressure of oxygen in an atmosphere above the sample which would be in equilibrium with this concentration) has been maintained at a measured value of 0.004 mm. Hg. Under this severe oxygen restriction, the saturation rates observed are as good as, and often better than ordinary aerobic rates. The suggestion that molecular oxygen per se enters into the mechanism of photosynthesis by way of a fast back-reaction is, therefore, rendered untenable. These results, coupled with the studies of Brown et al. with the mass spectrometer and isotopically labeled oxygen and with the work of Calvin et al. on the dilution of a C 14O 2 enriched gas phase with C 12O 2 from endogenous carbon, tend to discredit almost to the point of certainty the mechanism suggested by Burk and Warburg.