Photosynthetic Organisms - Plants, Algae, Cyanobacteria

28/02/2012 · OSCILLATORIA CYANOBACTERIA--PHOTOSYNTHETIC amun8isis

Cyanobacteria, also called blue-green algae, ..

N2 - The capacity for anoxygenic photosynthesis and other physiological traits related to sulfide tolerance were compared in several strains of the thermophilic cyanobacterium Oscillatoria amphigranulata. Strains were isolated from hot springs in which the environmental sulfide over O. amphigranulata microbial mats spanned a range from 0.2 to 1 mM. Great differences in the capacity for anoxygenic photosynthesis existed among the isolates but these correlated in a predictable manner with the sulfide content of the springs. The time required for commencement of anoxygenic photosynthesis and the degree of initial sensitivity of Photosystem II to sulfide did not correlate with environmental sulfide levels. Kinetic parameters of sulfide consumption indicate uniformly low affinities for sulfide (Km of about 1 mM) but differences among strains in Vmax.

An isolate from H2S-rich layers of the Solar Lake, the cyanobacterium Oscillatoria limnetica, exhibits both oxygenic and anoxygenic photosynthesis

Cyanobacteria | Cyanobacteria | Photosynthesis

AB - Anoxygenic cyanobacteria that use sulfide as the electron donor for photosynthesis are a potentially influential but poorly constrained force on Earth's biogeochemistry. Their versatile metabolism may have boosted primary production and nitrogen cycling in euxinic coastal margins in the Proterozoic. In addition, they represent a biological mechanism for limiting the accumulation of atmospheric oxygen, especially before the Great Oxidation Event and in the low-oxygen conditions of the Proterozoic. In this study, we describe the draft genome sequence of Geitlerinema sp. PCC 9228, formerly Oscillatoria limnetica 'Solar Lake', a mat-forming diazotrophic cyanobacterium that can switch between oxygenic photosynthesis and sulfide-based anoxygenic photosynthesis (AP). Geitlerinema possesses three variants of psbA, which encodes protein D1, a core component of the photosystem II reaction center. Phylogenetic analyses indicate that one variant is closely affiliated with cyanobacterial psbA genes that code for a D1 protein used for oxygen-sensitive processes. Another version is phylogenetically similar to cyanobacterial psbA genes that encode D1 proteins used under microaerobic conditions, and the third variant may be cued to high light and/or elevated oxygen concentrations. Geitlerinema has the canonical gene for sulfide quinone reductase (SQR) used in cyanobacterial AP and a putative transcriptional regulatory gene in the same operon. Another operon with a second, distinct sqr and regulatory gene is present, and is phylogenetically related to sqr genes used for high sulfide concentrations. The genome has a comprehensive nif gene suite for nitrogen fixation, supporting previous observations of nitrogenase activity. Geitlerinema possesses a bidirectional hydrogenase rather than the uptake hydrogenase typically used by cyanobacteria in diazotrophy. Overall, the genome sequence of Geitlerinema sp. PCC 9228 highlights potential cyanobacterial strategies to cope with fluctuating redox gradients and nitrogen availability that occur in benthic mats over a diel cycle. Such dynamic geochemical conditions likely also challenged Proterozoic cyanobacteria, modulating oxygen production. The genetic repertoire that underpins flexible oxygenic/anoxygenic photosynthesis in cyanobacteria provides a foundation to explore the regulation, evolutionary context, and biogeochemical implications of these co-occurring metabolisms in Earth history.

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

AB - Among the nitrogen (N2)-fixing cyanobacteria, the filamentous, nonheterocystous marine Oscillatoria spp. (Trichodesmium) appears enigmatic; it exhibits N2 fixation in the presence of oxygenic photosynthesis without structural protection of the N2-fixing apparatus (nitrogenase) from potential inhibition by molecular oxygen (O2). Characteristically, N2 fixation is largely confined to aggregates (bundles) of filaments. Previous work has suggested that spatial partitioning of photosynthesis and of N2 fixation occurs in the bundles as a means of allowing both processes to occur contemporaneously. The probing of freshly sampled bundles with O2 microelectrodes directly confirmed such partitioning by showing the presence of O2-depleted (reduced) microzones in photosynthetically active, N2-fixing bundles. Bundle size was directly related to both the development of internal reduced microzones and cellular N2 fixation rates. By enhancing microzone formation, bundles optimize N2 fixation as a means of supporting Oscillatoria spp. blooms in surficial, nitrogen-depleted tropical and subtropical waters.

switches to RC II and performs oxygenic photosynthesis (Oscillatoria is a member of the Cyanobacteria.


216 | Photosynthesis | Cyanobacteria

Among the nitrogen (N2)-fixing cyanobacteria, the filamentous, nonheterocystous marine Oscillatoria spp. (Trichodesmium) appears enigmatic; it exhibits N2 fixation in the presence of oxygenic photosynthesis without structural protection of the N2-fixing apparatus (nitrogenase) from potential inhibition by molecular oxygen (O2). Characteristically, N2 fixation is largely confined to aggregates (bundles) of filaments. Previous work has suggested that spatial partitioning of photosynthesis and of N2 fixation occurs in the bundles as a means of allowing both processes to occur contemporaneously. The probing of freshly sampled bundles with O2 microelectrodes directly confirmed such partitioning by showing the presence of O2-depleted (reduced) microzones in photosynthetically active, N2-fixing bundles. Bundle size was directly related to both the development of internal reduced microzones and cellular N2 fixation rates. By enhancing microzone formation, bundles optimize N2 fixation as a means of supporting Oscillatoria spp. blooms in surficial, nitrogen-depleted tropical and subtropical waters.

Oscillatoria - an overview | ScienceDirect Topics

The capacity for anoxygenic photosynthesis and other physiological traits related to sulfide tolerance were compared in several strains of the thermophilic cyanobacterium Oscillatoria amphigranulata. Strains were isolated from hot springs in which the environmental sulfide over O. amphigranulata microbial mats spanned a range from 0.2 to 1 mM. Great differences in the capacity for anoxygenic photosynthesis existed among the isolates but these correlated in a predictable manner with the sulfide content of the springs. The time required for commencement of anoxygenic photosynthesis and the degree of initial sensitivity of Photosystem II to sulfide did not correlate with environmental sulfide levels. Kinetic parameters of sulfide consumption indicate uniformly low affinities for sulfide (Km of about 1 mM) but differences among strains in Vmax.