Halotolerant Rhizobacteria for Salinity-Stress Mitigation: Diversity, Mechanisms and Molecular Approaches

Abstract

Agriculture is the best foundation for human livelihoods, and, in this respect, crop production has been forced to adopt sustainable farming practices. However, soil salinity severely affects crop growth, the degradation of soil quality, and fertility in many countries of the world. This results in the loss of profitability, the growth of agricultural yields, and the step-by-step decline of the soil nutrient content. Thus, researchers have focused on searching for halotolerant and plant growth-promoting bacteria (PGPB) to increase soil fertility and productivity. The beneficial bacteria are frequently connected with the plant rhizosphere and can alleviate plant growth under salinity stress through direct or indirect mechanisms. In this context, PGPB have attained a unique position. The responses include an increased rate of photosynthesis, high production of antioxidants, osmolyte accumulation, decreased Na+ ions, maintenance of the water balance, a high germination rate, and well-developed root and shoot elongation under salt-stress conditions. Therefore, the use of PGPB as bioformulations under salinity stress has been an emerging research avenue for the last few years, and applications of biopesticides and biofertilizers are being considered as alternative tools for sustainable agriculture, as they are ecofriendly and minimize all kinds of stresses. Halotolerant PGPB possess greater potential for use in salinity-affected soil as sustainable bioinoculants and for the bioremediation of salt-affected soil.

Plant Beneficial Deep-Sea Actinobacterium, Dermacoccus abyssi MT1.1T Promote Growth of Tomato (Solanum lycopersicum) under Salinity Stress

“…Osmoprotectants, or compatible solutes, are molecules produced by living organisms in response to several abiotic stresses including salinity [ 82 ]. Accumulation of compatible solutes is the mechanism for osmoregulation under salt stress in plants [ 5 , 10 ] and microorganisms [ 27 , 83 ]. They can be divided into four main classes; (1) the N-containing solutes such as proline and glycine betaine; (2) sugars such as sucrose and raffinose; (3) straight-chain polyhydric alcohols (polyols) such as mannitol and sorbitol; and (4) cyclic polyhydric alcohols (cyclic polyols) [ 5 ].…”

“…In addition, actinobacteria mitigate salt stress or enhance salt tolerance ability in plants using several strategies: 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, osmoregulation, and antioxidative defense/protection system. Osmoregulation can be achieved by the production of compatible solutes to relieve osmotic stress in plants under salt stress condition [ 27 ]. Common compatible solutes include amino acids (proline, glycine, and betaine) and sugars (sucrose and trehalose) [ 5 , 27 , 28 , 29 ].…”

“…Osmoregulation can be achieved by the production of compatible solutes to relieve osmotic stress in plants under salt stress condition [ 27 ]. Common compatible solutes include amino acids (proline, glycine, and betaine) and sugars (sucrose and trehalose) [ 5 , 27 , 28 , 29 ]. Inoculation of Streptomyces sp.…”

Improvement of Plant Responses by Nanobiofertilizer: A Step towards Sustainable Agriculture

“…It is one of the major sources of soil pollution, water pollution, and air pollution. Developing a cheap, nontoxic, and eco-friendly alternative to obtain high productivity in agriculture without any side effects is the need of the hour [ 99 ]. The biofertilizers are eco-friendly, cost-effective, sustainable, and have long-lasting effects.…”

Bioaugmentation Improves Phytoprotection in <em>Halimione Portulacoides </em>Exposed to Mild Salt Stress: Perspectives for Salinized Soil Restoration

“…The increase of the Ca concentration in the leaves could serve as an ionic balance mechanism, allowing the cell membrane to maintain the K/Na selectivity [43]. In fact, the uptake of K and Ca due to PGPR inoculation has been demonstrated to result in the up-regulation of the antioxidant system and mitigation of salt stress oxidative effects [48]. Furthermore, it has been described that rhizosphere inoculation by this halotolerant bacteria may confer salt tolerance through sequestering Na + into vacuoles, expelling Na + from roots, and, thru the exertion of a modulating effect in the ion transporters [49,50].…”