Saline microbiome: Biodiversity, ecological significance, and potential role in amelioration of salt stress

Worldwide, plant growth and productivity are majorly affected by the extreme environment of soil salinity, which is one of the major limiting factors. Numerous studies are increasing day by day to explore microbial diversity form saline environments and its application for crop improvements. Halophilic microbes are reported from diverse saline habitat including food crops growing under saline conditions, halophytic plants, saline lakes, sea, hypersaline soil, and mangrove. The microbiomes of saline habitats have the ability to survive in hypersaline conditions and colonized in rhizospheric/phyllospheric and internal tissue of plants. It promotes the plant growth by production of phytohormones and other important metabolites as well as produces some chemicals such as siderophore, hydrogen cyanide, ammonia, and hydrolytic enzymes for defenses of host plant from pathogenic microbes. The biodiversity of halophilic microbes will be illustrated in terms of different phylum, class, genera, and species and their mechanisms of action for the enhancement of plant growth, salt stress, and soil health for sustainable agriculture. All three domain archaea, bacteria and eukaryote with different phylum, e.g., Actinobacteria, Ascomycota, Bacteroidetes, Balneolaeota, Basidiomycota, Cyanobacteria, Euryarchaeota, Firmicutes, Proteobacteria (α/β/γ/δ), and Spirochaetes obtained from diverse saline habitat have been reported. Among all halophilic microbes, the phylum Firmicutes was found to be most dominant followed by Proteobacteria whereas phylum Balneolaeota was found less in numbers. The microbes with ecological significance were reported, e.g., many microbes such as Alternaria, Arthrobacter, Bacillus, Halobacillus, Halomonas, Oceanobacillus, Penicillium, Pseudomonas, and Sediminibacillus have been sorted out to be common at all site studies/survey, whereas microbes Alcaligenes, Amycolatopsis, Cladosporium, Haloarchaeobius, Myrothecium, Salinibacter, Soortia, and Spirochaeta have been reported as niche specific. This chapter is a critical and comprehensive review on biodiversity of microbiomes in saline environments, its ecological significance, and potential biotechnological applications for the betterment of salt stress, soil health, and plant growth for agriculture sustainability. These halophilic microbes help in promoting plant growth by increasing uptake of nutrients, plant growth and yield under the saline habitat, which could be utilized as biofertilizers/bioinoculants for crops growing in saline habitat.