Department of Microbiology, University of Kalyani, Kalyani, 741235, West Bengal, India.
World J Microbiol Biotechnol. 2021 Feb 5;37(3):39. doi: 10.1007/s11274-021-03003-8.
In this study, experiments were conducted to isolate, characterize, and evaluate rice rhizosphere bacteria for their arsenic (As) tolerance ability and zinc (Zn) solubilization potential in culture media and soil. Among 20 bacterial isolates recovered, six were found to solubilize inorganic Zn salt(s) efficiently under in vitro culture conditions. 16S rRNA gene sequence-based phylogenetic analysis indicated the affiliation of efficient Zn solubilizing bacteria (ZSB) to Burkholderia vietnamiensis and Burkholderia seminalis. Zinc solubilizing efficiency (ZSE) of the bacteria varied with the concentrations and types of Zn salts used in the experiments. Increasing trend in ZSE of the bacteria was noticed when the percentage of ZnO increased from 0.1 to 0.5 but the same decreased at 1.0%. Increased Zn solubilization was noticed when bacteria were incubated with lower concentration of Zn(PO) and ZnCO. In general, Zn solubilization increased with increasing incubation time in lower volume medium, while some isolates failed to solubilize one or more tested Zn salts. However, enriched concentrated cells of the ZSB in glucose amended medium with 0.5% ZnO showed an increasing trend of Zn solubilization with time and were able to solubilize more than 300 mg/L Zn. This increased rate of Zn release by the ZSB was attributed to marked decline in pH that might be due to the enhanced gluconic acid production from glucose. As evident from the decreased ZSE of the bacteria in the presence of As(V) in particular, it seems arsenic imparts a negative effect on Zn solubilization. The ZSB were also able to increase the rate of Zn release in soil. A microcosm-based soil incubation study amending the enriched bacteria and 0.5% ZnO in soil showed an elevated level of both water-soluble and available Zn compared to un-inoculated control. During Zn solubilization in microcosms, viable cells in terms of colony-forming unit (CFU) declined by the same order of magnitude both in the presence and absence of ZnO that might be due to the nutrients limiting condition aroused during the incubation period rather than Zn toxicity. The bacteria in this study also exhibited plant growth promoting traits, such as growth in nitrogen-free medium, production of indole acetic acid (IAA), and solubilization of potassium and phosphate. Our findings suggested that Burkholderia spp. could be the potential candidates for enhancing Zn dissolution in the soil that might reduce the rate of inorganic Zn fertilization in agricultural soil.
在这项研究中，进行了实验以分离、表征和评估水稻根际细菌对砷 (As) 的耐受性能力和在培养基和土壤中的锌 (Zn) 溶解能力。在回收的 20 个细菌分离物中，有 6 个在体外培养条件下有效地溶解无机 Zn 盐。基于 16S rRNA 基因序列的系统发育分析表明，高效 Zn 溶解细菌（ZSB）与越南伯克霍尔德氏菌和博克霍尔德氏菌属有关。细菌的 Zn 溶解效率（ZSE）随实验中使用的 Zn 盐浓度和类型而变化。当 ZnO 的百分比从 0.1 增加到 0.5 时，细菌的 ZSE 呈上升趋势，但在 1.0%时则下降。当细菌用较低浓度的 Zn(PO) 和 ZnCO 孵育时，Zn 溶解增加。一般来说，随着在低体积培养基中孵育时间的增加，Zn 溶解增加，而一些分离物未能溶解一种或多种测试的 Zn 盐。然而，在含 0.5% ZnO 的葡萄糖改良培养基中富集浓缩的 ZSB 细胞显示出随着时间的推移 Zn 溶解的增加趋势，并且能够溶解超过 300 mg/L 的 Zn。ZSB 释放 Zn 的这种增加速度归因于 pH 的显著下降，这可能是由于葡萄糖产生的葡萄糖酸增加所致。从细菌在 As(V)存在下的 ZSE 降低可以明显看出，砷似乎对 Zn 溶解产生负面影响。ZSB 还能够增加土壤中 Zn 的释放速度。在土壤中添加富集细菌和 0.5% ZnO 的微宇宙培养研究表明，与未接种对照相比，水溶性和有效 Zn 的水平均升高。在微宇宙中 Zn 溶解过程中，无论是在存在还是不存在 ZnO 的情况下，以菌落形成单位（CFU）表示的活菌数量都按相同的数量级下降，这可能是由于在培养期间出现了限制营养的条件，而不是 Zn 毒性。本研究中的细菌还表现出植物生长促进特性，例如在无氮培养基中生长、产生吲哚乙酸（IAA）以及溶解钾和磷酸盐。我们的研究结果表明，伯克霍尔德氏菌属可能是增强土壤中 Zn 溶解的潜在候选者，这可能会降低农业土壤中无机 Zn 施肥的速度。
