Differential Responses of Nitrogen-Fixing Cyanobacteria to Salinity and Osmotic Stresses

Abstract

Two nitrogen-fixingAnabaena strains were found to be differentially tolerant to salinity and osmotic stresses. Anabaena torulosa, a brackish-water, salt-tolerant strain, was relatively osmosensitive. Anabaena sp. strain L-31, a freshwater, salt-sensitive strain, on the other hand, displayed significant osmotolerance. Salinity and osmotic stresses affected nitrogenase activity differently. Nitrogen fixation in both of the strains was severely inhibited by the ionic, but not by the osmotic, component of salinity stress. Such differential sensitivity of diazotrophy to salinity-osmotic stresses was observed irrespective of the inherent tolerance of the two strains to salt-osmotic stress. Exogenously added ammonium conferred significant protection against salinity stress but was ineffective against osmotic stress. Salinity and osmotic stresses also affected stress-induced gene expression differently. Synthesis of several proteins was repressed by salinity stress but not by equivalent or higher osmotic stress. Salinity and osmotic stresses induced many common proteins. In addition, unique salt stressor osmotic stress-specific proteins were also induced in both strains, indicating differential regulation of protein synthesis by the two stresses. These data show that cyanobacterial sensitivity and responses to salinity and osmotic stresses are distinct, independent phenomena.

Cyanophycin and glycogen synthesis in a cyanobacterial Scytonema species in response to salt stress

“…Indeed the inhibition of growth with increasing salt concentrations was paralleled by a loss of nitrogen ¢xation (acetylene reduction; Fig. 1), consistent with the observations of Fernandes [20].…”

The marine cyanobacterium Crocosphaera watsonii WH8501 synthesizes the compatible solute trehalose by a laterally acquired OtsAB fusion protein

“…In contrast to the picoplanktonic cells, Crocosphaera is able to fix dinitrogen making the cell independent from the external nitrogen amount. An increased salt resistance under non-nitrogen-fixing growth conditions was also reported for N 2-fixing Anabaena strains (Fernandes et al, 1993).…”

Effect of salinity changes on the bacterial diversity, photosynthesis and oxygen consumption of cyanobacterial mats from an intertidal flat of the Arabian Gulf

“…Cyanobacteria were shown to tolerate high salinities by accumulating inorganic (K + ions) and organic (sugars, polyols, and quaternary amines, etc.) osmoregulators intracellularly in order to reach an osmotic equilibrium with the surrounding environment (Blumwald and Tel-Or, 1983;Mackay et al, 1983;Reed et al, 1984;Csonka, 1989;Fernandes et al, 1993;Galinsky, 1995). The production of these compounds requires a reallocation of a significant fraction of cell resources, consequently affecting other metabolic processes (Pinckney et al, 1995).…”

“…Microcoleus, Anabaena and Spirulina spp.) showed a significant reduction in rates of processes like photosynthesis, respiration and nitrogen fixation by osmotic stress (Vonshak et al, 1988;Fernandes et al, 1993;Karsten, 1996). However, extrapolation of physiological adaptations of individual microorganisms to complex natural bacterial communities, where various metabolic processes closely interact, may not always be valid.…”