Strategies for the salt tolerance in bacteria and archeae and its implications in developing crops for adverse conditions

Abstract

Salinity is one of the major problems limiting the crop productivity worldwide. Interestingly, halophiles are an interesting class of organisms adapted to moderate and hyper saline environments. In Archaea, the most salt-requiring microorganisms belong to halobacteria. Halophiles can be distinguished into different following categories: extreme halophiles (2.5-s5.2 M salt), borderline extreme halophiles (1.5-4.0 M salt), moderate halophiles (0.5-2.5 M salt), and halotolerant microorganisms that do not require salt for growth but grow well up to reasonably high salt concentrations. The extreme halotolerant groups have growth range above 2.5 M salt. The halophilic proteins are highly acidic in nature and majority would denature in low salt concentration. Most halophilic bacteria and the halophilic methanogenic archaea a number of such organic solutes like glycine betaine, ectoine and other amino acid derivatives, sugars and sugar alcohols. Bacteria and Archaea have developed two basic mechanisms to cope with osmotic stress. The “salt-in-cytoplasm mechanism” involves adjusting the salt concentration in the cytoplasm. The “organic-osmolyte mechanism” involves accumulation of uncharged and highly water-soluble organic compounds to maintain an osmotic equilibrium with the surrounding medium which can be exploited for developing stress-tolerant crop varieties.