Plant growth-promoting rhizobacteria are a group of free-living bacteria that colonize plant rhizosphere and benefit plant root growth, thereby increasing host plant to cope with salinity induced stress. The aim of this study was to (1) isolate and characterize auxin-producing bacteria showing a high plant growth-promoting (PGP) potential, and (2) evaluate the PGP effects on the growth of Medicago sativa L under salinity stress (130 mM NaCl). Of thirteen isolates, Bacillus megaterium NRCB001 (NRCB001), B. subtilis subsp. subtilis NRCB002 (NRCB002) and B. subtilis NRCB003 (NRCB003) had the ability to produce auxin, which ranged from 47.53 to 154.38 μg ml⁻¹. The three auxin-producing bacterial strains were shown multiple PGP traits, such as producing siderophore and NH₃, showing ACC deaminase activity, solubilize phosphate and potassium. Furthermore, NRCB001, NRCB002, and NRCB003 could survive in LB medium containing 1750 mM NaCl. The three auxin-producing with salinity tolerance strains were selected for further analyses. In greenhouse experiments, when inoculated with NRCB001, NRCB002 and NRCB003, dry weight of alfalfa significantly (P < 0.05) increased by 24.1%, 23.1% and 38.5% respectively, compared with those of non-inoculated control seedlings under normal growth condition. When inoculated with NRCB002 and NRCB003, dry weight of alfalfa significantly (P < 0.05) increased by 96.9 and 71.6% respectively, compared with those of non-inoculated control seedlings under 130 mM NaCl condition. Our results indicated that NRCB002 and NRCB003 having PGP traits are promising candidate strains to develop biofertilizers, especially used under salinity stress conditions.

促进植物生长的根际细菌是一类自由生活的细菌，它们定植在植物根际中并有利于植物根部生长，从而增加宿主植物以应对盐分诱导的胁迫。这项研究的目的是（1）分离并鉴定具有高植物生长（PGP）潜力的生长素生成细菌，以及（2）评价PGP对盐胁迫（130 mM）下紫花苜蓿L的生长的影响。NaCl）。在十三种分离物中，巨大芽孢杆菌NRCB001（NRCB001），枯草芽孢杆菌亚种。枯草芽孢杆菌NRCB002（NRCB002）和枯草芽孢杆菌NRCB003（NRCB003）具有产生植物生长素的能力，范围为47.53至154.38μgml ^-1。这三个生长素的细菌菌株显示出多个PGP性状，例如产生铁载体和NH ₃，显示出ACC脱氨酶活性，溶解了磷酸盐和钾。此外，NRCB001，NRCB002和NRCB003可以在含有1750 mM NaCl的LB培养基中存活。选择了三种具有盐度耐受性的生长素生产菌株用于进一步分析。在温室试验中，接种NRCB001，NRCB002和NRCB003后，紫花苜蓿的干重 与正常生长条件下未接种的对照幼苗相比分别显着增加（P <0.05）24.1％，23.1％和38.5％。接种NRCB002和NRCB003后，苜蓿的干重显着（P <0.05）与在130 mM NaCl条件下未接种的对照幼苗相比，分别增加了96.9和71.6％。我们的结果表明，具有PGP特性的NRCB002和NRCB003是有望开发生物肥料的候选菌株，特别是在盐分​​胁迫条件下使用。