Domestication Of Salt-tolerant Microorganisms Under Different Salinity Conditions And Their Performance

Soil salinization has caused a large decrease in the total cultivated land.Thus,alleviating the inhibitory effects of salt stress on plant growth is becoming more and more important.At present,the method of saline–alkali soil improvement mainly includes water improvement,farming technology improvement,addition of chemicals and plant improvement,etc.However,it's difficult to achieve an expected effect in the management of saline-alkali soil due to the high implementation cost,long time cycle and the unsustainability of these methods.Therefore,an effective method to alleviate salt stress is needed to remedy the above shortcomings.In this study,salt-tolerant bacteria were screened from saline soil to act on plants and alleviate the inhibitory effects of salt stress on plant growth.Isolation and purification of salt-tolerant microorganisms: salt-tolerant strains were isolated from saline soil samples on an Anaerobic broth medium and a Marine broth 2216 medium containing 2% of Na Cl through plate scribing method,which was purified through zonal scribing method.Identification and screening of salt-tolerant microorganisms: an analysis of 16 S r DNA gene sequences was applied to identify the isolates.The nucleotide sequences of each strain were respectively compared with the data in National Center for Biotechnology Information Gen Bank database and a developmental tree was constructed.These strains were initially understood by reviewing the literature and finally 3 strains(Bacillus velezensis,Bacillus thuringiensis and Brevibacterium frigoritolerans)were selected for subsequent experiments.Domestication of salt-tolerant microorganisms: the experimental strains were cultured and domesticated step by step in Na Cl with a concentration of 4-10% to enable them to tolerate the high salt stress.The microbial activity was measured under different salinity domestication conditions through a UV spectrophotometer,so as to determine their stable growth under salt stress.The experimental results showed that all the domesticated strains were able to tolerate a salt stress of 10%,and also showing a stable growth trend with different Na Cl concentrations.Thus,the domesticated strains were able to adapt to adverse salt stress conditions and protect their hosts against salt stress environments.Plant growth-promoting characteristics: the ability of the experimental strains to promote plant growth was determined by measuring their plant growth-promoting characteristics in Na Cl with a concentration of 0-10%.The results showed that B.velezensis had a positive 1-aminocyclopropane-1-carboxylic acid(ACC)deaminase activity and indole-3-acetic acid(IAA)production;B.thuringiensis had a positive IAA production,phosphate solubilization and nitrogen fixation;and B.frigoritolerans had a positive ACC deaminase activity,IAA production,phosphate solubilization and siderophore.Each of the experimental strains had two or more plant growth-promoting characteristics,which were well complementary.Pot experiment: the test plants were planted in soil with different Na Cl concentrations(0,50,100,200,300 and 400 m M)to explore the promotion effect of single or co-inoculation of the experimental strains on plant growth under different salt stresses.The results showed that the order of effect of inoculation was co-inoculation > single inoculation > control.For a single inoculation,the wheat inoculated with B.frigoritolerans showed the best performance of plant growth promotion.