Involvement of Photosystem II in the ammonia metabolism of a heterotrophic cyanobacterium

Ammonium photo-production by heterocytous cyanobacteria: potentials and constraints

Over the last decades, production of microalgae and cyanobacteria has been developed for several applications, including novel foods, cosmetic ingredients and more recently biofuel. The sustainability of these promising developments can be hindered by some constraints, such as water and nutrient footprints. This review surveys data on N2-fixing cyanobacteria for biomass production and ways to induce and improve the excretion of ammonium within cultures under aerobic conditions. The nitrogenase complex is oxygen sensitive. Nevertheless, nitrogen fixation occurs under oxic conditions due to cyanobacteria-specific characteristics. For instance, in some cyanobacteria, the vegetative cell differentiation in heterocyts provides a well-adapted anaerobic microenvironment for nitrogenase protection. Therefore, cell cultures of oxygenic cyanobacteria have been grown in laboratory and pilot photobioreactors (Dasgupta et al., 2010; Fontes et al., 1987; Moreno et al., 2003; Nayak & Das, 2013). Biomass production under diazotrophic conditions has been shown to be controlled by environmental factors such as light intensity, temperature, aeration rate, and inorganic carbon concentration, also, more specifically, by the concentration of dissolved oxygen in the culture medium. Currently, there is little information regarding the production of extracellular ammonium by heterocytous cyanobacteria. This review compares the available data on maximum ammonium concentrations and analyses the specific rate production in cultures grown as free or immobilized filamentous cyanobacteria. Extracellular production of ammonium could be coupled, as suggested by recent research on non-diazotrophic cyanobacteria, to that of other high value metabolites. There is little information available regarding the possibility for using diazotrophic cyanobacteria as cellular factories may be in regard of the constraints due to nitrogen fixation.

Occurrence of the 32-kDa QB-binding protein of photosystem II in vegetative cells, heterocysts and akinetes ofAzolla carotiniana cyanobionts

Transmission electron microscopy and immunocytological labeling were used to localize the 32-kilodalton (kDa) protein (DI polypeptide) of photosystem II in different cell types of the cyanobionts within leaf cavities ofAzolla caroliniana Willd. The 32-kDa protein binds the secondary electron acceptor QB, and is highly conserved between plants and cyanobacteria. Three antisera, specific for different epitopes of the 32-kDa protein, were used as primary antibodies. Immunologically recognizable 32-kDa protein was localized on membranes ofAzolla chloroplasts, vegetative cyanobacterial cells, akinetes, and heterocysts that were at all stages of the differentiation process. The 32-kDa protein was not detected in nonphotosynthetic endosymbiotic bacteria found within leaf cavities. The amount of the 32-kDa protein observed in different cyanobacterial cell types was dependent upon the primary antiserum used and membrane orientation within a cell with respect to the plane of sectioning. Therefore, although 32-kDa protein was present in all three cyanobacterial cell types and clear trends in labeling patterns could be elucidated, it was not possible to quantitate the amounts of protein with respect to either cell type or leaf-cavity age.