Interaction Mechanism With Enterobacter Cloacae Rs-2 On Regulation Of Bacillus Subtilis SL-44 Siderophore Producing

As an important bioactive substance secreted by soil microorganisms,siderophore can efficiently chelate soil Fe（III）and promote its conversion into Fe（II）that can be absorbed by plants,thereby improving the absorption of iron ions in the soil and promoting plant photosynthesis and nutrient accumulation.Previous studies have shown that in the development and application of microbial agents,a single strain producing siderophore has shortcomings such as poor stability,single performance,and low applicability.The previous research of the research team showed that the mixed culture of Bacillus subtilis SL-44 and Enterobacteriaceae cloacae Rs-2 screened from the rhizosphere soil of saline cotton fields in Xinjiang could significantly increase the content of siderophore,but the rule of the synthesis of siderophore in this co culture system and the internal regulation mechanism of strain interaction on the synthesis of siderophore have not yet been explored.Research has found that Bacillus subtilis SL-44 can synthesize secondary metabolites that are beneficial for plant growth,including indole-3-acetic acid（IAA）,siderophore,and organic acids that promote soil phosphorus conversion.In vitro antibacterial experiments have shown that SL-44 has high antibacterial activity against Rhizoctonia solani（R.solani）.Through annotation and analysis of the entire SL-44 genome,it was found that a large number of genes are involved in antioxidant stress,antibiotic and toxin synthesis.At the same time,using Anti SMASH 6.0 online platform analysis,the biosynthetic gene cluster of secondary metabolites such as baillibactin was identified.By exploring the influencing factors of regulating the secretion of siderophore in the co culture system,it was found that the iron content in the culture medium would significantly affect the synthesis of siderophore.When the content of Fe³⁺is less than 10μM,it can induce the release of siderophore,whereas it can inhibit it.The Casky and Arnow experiments showed that SL-44 mainly synthesized catechol type siderophore,while Rs-2 mainly synthesized hydroxamic acid type siderophore.The co-culture system of the two strains mainly synthesized catechol type siderophore,indicating that the interaction between the two is manifested as the induction of SL-44 siderophore synthesis by Rs-2.Furthermore,through differential gene expression analysis,it was found that both the secondary metabolites of Rs-2 and EPS can indirectly promote siderophore synthesis by downregulating the expression of Fur family transcription regulators related genes in SL-44,alleviating the inhibition of siderophore synthesis.The extracellular polymer of Rs-2 can directly promote siderophore synthesis by upregulating the expression of genes related to siderophore secretion.Through seed germination experiments and pot experiments,pea was used as the research object,and treated with a co culture system and crude iron extract of SL-44.The results showed that the co culture system of iron producing strains could effectively promote the germination and plant growth of pea seeds.When co cultured at 9:1（SL-44:Rs-2）,the germination rate of pea seeds was 100%,and the vitality index increased by 24.4%.After treatment with crude iron extract,the total chlorophyll content in pea leaves increased by87.0%,and soil sucrase（S-SC）increased by 1.32 times.The generated siderophore can also alleviate the iron deficiency response mechanism of plants by converting Fe（III）into available Fe（II）that can be utilized by plants.In summary,the analysis of the entire genome data provides clear evidence indicating the enormous potential of Bacillus subtilis SL-44 produce various biological antagonistic natural products and promoting metabolic products,which may contribute to further research on effective treatment measures for plant biological control.The mixture of Bacillus subtilis SL-44 and Enterobacteriaceae cloacae Rs-2 can give full play to the advantages of siderophore-producing rhizogenic bacteria.At the same time,the interaction mechanism of two strains producing siderophore was preliminarily explored,which revealed for the first time that siderophore enhanced soil enzyme activity,improved soil nutrient transformation,promoted pea biomass accumulation,and had potential application value in biological fertilizer development and bioremediation of iron deficient soil.