Adaptation of cyanobacteria to environmental stimuli: new steps towards molecular mechanisms

Abstract

Dating from the Pre‐Cambrian era, cyanobacteria have a long history of adaptation to the Earth's environment. By evolving oxygen via photosynthetic reactions similar to those of plants and green algae, these prokaryotes were essential to the evolution of the present biosphere. They continue to make a large contribution to the equilibrium of the Earth's atmosphere by production oxygen and removing carbon dioxide. To survive in extreme or variable environments, cyanobacteria have developed specific regulatory systems, in addition to more general mechanisms equivalent to those of other prokaryotes or photosynthesis eukaryotes. Specific regulatory systems control the differentiation of specialized nitrogen‐fixing cells and of cell types facilitating the dispersion of species. In the past decade, considerable progress has been made towards understanding the expression of the cyanobacterial genome in response to variations in the intensity and spectral quality of incident light and in response to nutritional conditions, especially carbon, nitrogen and sulphur sources. These studies have provided insights into the relationships between carbon and nitrogen intermediary metabolism, and a start towards understanding of the interconnected pathways which lead from the perception of environmental signals to the regulation of enzyme activities and gene expression. Cyanobacterial regulatory mechanisms share common features with those of other prokaryotes, but are unique since these essentially photo‐autotrophic organisms must maintain a proper cellular C/N balance, in spite of dailty variations in incident light. Thus an appropriate coordination between photosynthesis and other metabolic processes must be achieved through control of the catalytic activity of key enzymes by reducing equivalents and ATP produced by photosynthetic or respiratory electron transport. Recently discovered kinases/phosphatases act by post‐translational modification of specific proteins which probably act as signal transducers or modulators of gene expression in a manner similar to the well‐known two‐component regulatory systems described in other bacteria. In this overview, we present our current knowledge on the molecular aspects of the biology of cyanobacteria, as well as on their mechanisms of resistance to metal ions and their responses to metabolic stress.

Recent Applications of Metabolomics Toward Cyanobacteria

“…The growth and metabolic activities of cyanobacteria are determined and influenced by diverse environmental factors such as light, temperature, salinity, and the availability of different C or N sources [91,92]. Transcriptomics revealed increased or decreased expression of defined groups of genes for certain biochemical routes, i.e.…”

Evaluation of the Antioxidant Activity of Cell Extracts from Microalgae

“…Microalgae are the basis of the food chain in aquatic ecosystems; with the aid of solar energy, they can use H 2 O and CO 2 to synthesize complex organic compounds—and subsequently accumulate and/or secrete many primary and secondary metabolites of interest [4,5,6]. Furthermore, microalgae exhibit adaptative responses to oxidative stresses, via stimulation of their antioxidant defence system [7] that consists of both enzymatic and non-enzymatic mechanisms: superoxide dismutase, catalase, glutathione reductase and ascorbate peroxidase are key enzymes in the former, whereas the non-enzymatic counterpart includes such mediator compounds as ascorbic acid, reduced glutathione, tocopherols, carotenoids and phycocyanin [8].…”

Enigmatic Microorganisms and Life in Extreme Environments

“…They have a world-wide distribution and colonize many terrestrial (neutral and alkaline) and aquatic (limnic and marine) habitats, from polar to tropical areas of the globe (Carr and Whitton, 1982;Dodds et aI., 1995;Stal, 616 1995;Bergman, 1996;Capone et al, 1997). Many cyanobacteria can also adjust to a variety of extreme growth conditions such as salt marshes, hot springs or deserts (Carr and Whitton, 1982;Dodds et al, 1995) and can withstand many abiotic stresses (Tandeau de Marsac and Houmard, 1993;Grossman et al, 1994;Potts, 1996).…”