Plant growth-promoting rhizobacteria (PGPR) are known to improve plant growth and are used as biofertilizers, thanks to their numerous benefits to agriculture such as phosphorus solubilization and phytohormone production. In this paper, four rhizospheric bacteria (Phyllobacterium sp., Bacillus sp., Agrobacterium sp., and Rhizobium sp.) isolated from surface-sterilized root nodules of Acacia cyanophylla were tested for their ability to solubilize inorganic phosphate and to produce indole-3-acetic acid (IAA) under laboratory conditions. Then, the best IAA producer (Rhizobium sp.) was selected to test optimized conditions for IAA production. Finally, the effect of the four strains on plant growth for A. cyanophylla was evaluated in vivo. The results showed that the totality of the tested isolates had solubilized inorganic phosphate (P) in both NBRIP (National Botanical Research Institute Phosphate) and PVK (Pikovskaya) media. Bacillus sp. was a high P-solubilizer and showed maximum solubilization in PVK (519 μg ml-1) and NBRIP (782 μg ml-1). The optimization of maximum phosphate solubilization was done using different sources of carbon (1%) and nitrogen (0.1%). Glucose and ammonium sulfate were selected to be the best carbon and nitrogen source for phosphate solubilization by all tested strains, except for Phyllobacterium sp., which recorded the highest phosphate solubilization with ammonium nitrate. The IAA production by the tested strains indicated that Rhizobium sp. produced the highest amount of IAA (90.21 μg ml-1) in culture media supplemented with L-tryptophan. The best production was observed with L-Trp concentration of 0.2% (116.42 μg ml-1) and at an initial pH of 9 (116.07 μg ml-1). The effect of NaCl on IAA production was tested at concentrations of 0 to 5% and the maximum production of 89.43 μg ml-1 was found at 2% NaCl. The extraction of crude IAA from this strain was done and purity was confirmed with Thin Layer Chromatography (TLC) analysis. A specific spot from the extracted IAA production was found to correspond with a standard spot of IAA with the same Rf value. Finally, the tested PGPR demonstrated growth stimulatory effects on Acacia cyanophylla seedlings in vivo, with a great increase of shoots’ and roots’ dry weights, and shoot length compared to control. The rhizobacterial isolates were identified by 16S rDNA sequence analysis as Agrobacterium sp. NA11001, Phyllobacterium sp. C65, Bacillus sp. CS14, and Rhizobium sp. V3E1. This study highlights the importance of the use of phosphate solubilizing and IAA producer microorganisms as biofertilizers to increase crop yields. The studied strains showed a significant phosphate solubilization potential and IAA production. The use of selected strains as inoculants would be interesting, in particular with a view of promoting sustainable agriculture. However, further studies to verify the efficacy of the best isolates in situ is certainly required.

中文翻译：

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蓝藻相思根瘤菌根瘤菌菌株筛选并优化吲哚-3-乙酸的产生和磷酸化及其对植物生长的影响

众所周知，促进植物生长的根际细菌（PGPR）可以改善植物的生长，并被用作生物肥料，这归功于它们对农业的诸多好处，例如磷的溶解和植物激素的生产。在本文中，测试了从蓝藻相思的根瘤根结节中分离出的四种根际细菌（Phyllobacterium sp。，芽孢杆菌属，农杆菌属和根瘤菌）的溶解无机磷酸盐和生产吲哚3的能力。 -乙酸（IAA）在实验室条件下。然后，选择最佳的IAA生产商（Rhizobium sp。）来测试IAA生产的最佳条件。最后，在体内评估了四种菌株对蓝藻A.植物生长的影响。结果表明，在NBRIP（国家植物科学研究所磷酸盐）和PVK（Pikovskaya）培养基中，所有测试菌株均具有溶解的无机磷酸盐（P）。芽孢杆菌 是高P增溶剂，在PVK（519μgml-1）和NBRIP（782μgml-1）中显示最大增溶作用。使用不同来源的碳（1％）和氮（0.1％）进行了最大磷酸盐增溶的优化。在所有测试菌株中，葡萄糖和硫酸铵被选为最佳的磷和碳氮源，除了幽门螺杆菌（Phyllobacterium sp。）记录的最高的磷酸盐溶解度是硝酸铵。通过测试菌株的IAA生产表明根瘤菌属。在补充了L-色氨酸的培养基中产生了最高量的IAA（90.21μgml-1）。在0.2％（116.42μgml-1）的L-Trp浓度和9（116.07μgml-1）的初始pH下观察到最佳产量。在0至5％的浓度下测试了NaCl对IAA产生的影响，在2％NaCl下发现最大产生量为89.43μgml-1。从该菌株中提取了粗制IAA，并通过薄层色谱（TLC）分析确认了纯度。发现从提取的IAA生产中得到的特定斑点与具有相同Rf值的IAA标准斑点相对应。最后，测试的PGPR显示出对体内金合欢幼苗的生长刺激作用，与对照相比，芽和根的干重以及茎长大大增加。通过16S rDNA序列分析将根瘤菌分离物鉴定为农杆菌属。NA11001，毛状杆菌属。C65，芽孢杆菌 CS14和根瘤菌sp。V3E1。这项研究强调了使用磷酸盐增溶剂和IAA生产者微生物作为生物肥料以增加农作物产量的重要性。所研究的菌株显示出显着的磷酸盐增溶潜力和IAA产生。使用选定的菌株作为孕育剂将是有趣的，特别是在促进可持续农业方面。但是，肯定需要进一步的研究以验证最佳分离物的原位功效。特别是为了促进可持续农业。但是，肯定需要进一步的研究以验证最佳分离物的原位功效。特别是为了促进可持续农业。但是，肯定需要进一步的研究以验证最佳分离物的原位功效。