Enhancement of Cyanobacterial Salt Tolerance by Combined Nitrogen

Abstract

Presence of certain nitrogenous compounds in the growth medium significantly enhanced the salt tolerance of the freshwater cyanobacterium Anabaena sp. strain L-31 as well as the brackish water cyanobacterium Anabaena torulosa. Among these, nitrate, ammonium, and glutamine were most effective followed by glutamate and aspartate. These nitrogenous compounds also inhibited Na influx in both Anabaena spp. with the same order of effectiveness as that observed for protection against salt stress. The inhibition of Na+ influx on addition of the nitrogenous substances was rapid; nitrate and ammonium inhibited Na+ influx competitively. Proline and glycine did not affect Na+ influx and also had no influence on the salt tolerance of either Anabaena sp. The observed protection was not consequent to a stimulatory effect of combined nitrogen on growth per se. Uptake of N03-and NH4+ increased during salt stress but was not correlated with growth. Intracellular levels of N03-and NH4+ were found to be inadequate to constitute a major component of the intemal osmoticum. The results suggest that inhibition of Na+ influx by combined nitrogen is a major mechanism for protection of cyanobacteria against salt stress.

Salt acclimation of Nodularia spumigena CCY9414—a cyanobacterium adapted to brackish water

“…As was found for related strains of the Nostocales (Reddy et al 1989, Fernandes et al 1993, Moisander et al 2002, the growth of Nodularia CCY9414 is clearly diminished in media containing more than 20 g NaCl l −1 . However, in sharp contrast to the studies with freshwater strains of Nostocales that always showed the highest growth rates under NaCl-free conditions, the Baltic Sea isolate Nodularia CCY9414 showed optimal growth after addition of ~10 g NaCl l −1 and decreased rates under low-salt conditions.…”

The oxidative stress caused by NaCl inAzolla carolinianais mitigated by nitrate

“…Under the condition, i.e. in the presence of nitrate, the contribution of cyanobacterial fixed nitrogen is then negligible (Reddy et al 1989;Rai and Abraham 1995). In contrary, Azolla-Anabaena relationship is tolerant to repression by combined nitrogen (Peters 1978;Mostafa and Hassan 2006).…”

“…In contrary, Azolla-Anabaena relationship is tolerant to repression by combined nitrogen (Peters 1978;Mostafa and Hassan 2006). It has been reported reduction in the NaCl-induced growth inhibition of cyanobacteria by nitrate and the reason given is that NO À 3 and Na ' share a common transport system (Reddy et al 1989;Rai and Tiwari 1999). Thus, nitrate protects the growth of Azolla plants by its own enhanced uptake and consequent reduction of Na ' entry into the cells (Rai and Rai 2003).…”

A role for osmotic stress-induced proteins in the osmotolerance of a nitrogen-fixing cyanobacterium, Anabaena sp. strain L-31

“…The possibility of modifying the inherent salt or osmotic tolerance of organisms has been revealed through phenomena such as adaptation and cross-protection (3,11,12,15). This has opened up the possibility of investigating the correlation between the expression of osmotic-stress-induced proteins (OSPs) and cyanobacterial osmotolerance.…”

“…These include (i) exclusion of Na' (3,15) and (ii) accumulation of inorganic osmolytes such as K+ (17) or organic osmolytes such as sugars, polyols, and quaternary amines (6,7,13,16). In most organisms osmotic stress evokes an adaptive response, initiated by stress-regulated gene expression and culminating in certain structural and functional alterations suited for survival under osmotic stress (1,10,12,19,20).…”