Classification And Genome Analysis Of An Endophytic Aquibacillus

Many endophytes can not only promote plant growth,but also improve seed germination rate,root growth of the host.The study can provide important theoretical support for the utilization of plant endophytic growth-promoting bacteria.In this study,a strain HU2P27^Tisolated from the stem of Kalidium cuspidatum collected in Tumd Right Banner,Inner Mongolia,was identified by multiphase classification.The main results are as follows:（1）Strain HU2P27^Twas Gram-stain-positive,strictly aerobic,motile,endospore-forming,milk-white,rod-shaped 0.5-0.7μm wide,2.0-4.0μm long.Strain grew at 10-40℃（optimum,30℃）,at p H 6.0-9.0（optimum,p H 7.0）and with0-14.0%Na Cl（optimum,5.0-8.0%）.The strain tested positive for oxidase,catalase,urease,methyl red reaction and nitrate reductase,but twain-80 and Voges Proskauer reaction were negative.Strain HU2P27^Tcontained MK-7 as the major respiratory quinone.Its major fatty acids were anteiso-C_15:0and iso-C_15:0,and the major polar lipids were phosphatidylglycerol,diphosphatidylglycerol and four unidentified phospholipids.The cell wall of strain HU2P27^Twas determined to contain peptidoglycan with meso-diaminopimelic acid as the diagnostic diamino acid.The phylogenetic trees based on the 16S r RNA gene sequence and the core genome both showed that strain HU2P27^Tclustered with Aquibacillus koreensis BH30097^T,sharing 97.7%and<97.0%of 16S r RNA gene similarity with A.koreensis BH30097^Tand any other type strain.The average nucleotide identity,amino acid identity and digital DNA-DNA hybridization values of strain HU2P27^Twith A.koreensis BH30097^Twere 71.7,69.2 and 19.4%.The strain HU2P27^Twas identified as a new species of Aquibacillus based on phylogenetic analysis and physiological and biochemical characteristics,named Aquibacillus kalidii sp.nov.The genomic DNA G+C content was 36.0mol%.（2）The strain HU2P27^Tcould produce IAA,after 72h culture in DF medium,the strain could produce 9.403±0.312 mg/L IAA.The strain could secrete siderophores.（3）The functional gene analysis of strain HU2P27^Tshowed that strain HU2P27^Tsynthesized IAA through the tryptophan dependent pathway,and the type of siderophores synthesized was catechol salt.In addition,there are multiple genes involved in resistance to antibiotics and toxic compounds;flagellar movement and related genes that accept methylation contribute to bacterial migration and colonization.In addition,strain HU2P27^Tcan synthesize small organic molecules such as choline and betaine to maintain osmotic pressure balance and adapt to the adverse extracellular environment such as high salinity.