The widespread use of hexavalent chromium Cr(VI) in the leather industry causes substantial environmental problems when effluents are left untreated. Therefore, the present work attempts to assess the ability of Bacillus thuringiensis (V45) and Staphylococcus capitis (S21), isolated from tannery industry sediment, to detoxify Cr(VI) by reducing the oxidation state. Initially, the minimum tolerance of chromium by both bacteria was found up to 1000 μg/mL. V45 could tolerate Cr(VI) (520 μg/mL), and S21 could also tolerate hexavalent Cr(VI) (340 μg/mL). Similarly, both bacteria were able to tolerate other metals such as Hg²⁺ (40 μg/mL), Cu²⁺ (30 μg/mL), Ni²⁺ (60 μg/mL), Zn²⁺ (40 μg/mL), and Pb²⁺ (30 μg/mL). V45 and S21 could decrease Cr(VI) at a primary concentration of 50 μg/mL up to 86.42% and 97.34%, respectively. In optimization experiments, the best temperature to decrease Cr(VI) was shown to be 35 °C with pH 7 for 96 h. The occurrence of Cu²⁺ and Na⁺ slightly increased during the decrease of hexavalent Cr(VI) by V45, while the isolate S21 exhibited the same effects with Cu²⁺, Mn²⁺, and Na⁺. The carboxylate and amino conjugates in the biomass are intricate in the bioreduction of Cr(VI), as confirmed by FTIR spectroscopy. In addition, SEM imagery revealed the accumulation of Cr(VI) around both types of bacterial cells. The occurrence of other elements was evident from SEM-EDS spectroscopy. This study demonstrated the ability of native bacterial populations (V45 and S21) in tannery sediment to reduce Cr(VI) compounds.

Graphical abstract

中文翻译：

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从制革厂沉淀物中分离的苏云金芽孢杆菌和金黄色葡萄球菌对六价铬污染的废水进行生物修复

当皮革废水未经处理时，六价铬Cr（VI）在皮革工业中的广泛使用会引起严重的环境问题。因此，本工作试图评估从制革业沉积物中分离的苏云金芽胞杆菌（V45）和葡萄球菌（S21）通过降低氧化态来解毒Cr（VI）的能力。最初，发现两种细菌对铬的最小耐受量均高达1000μg/ mL。V45可以耐受Cr（VI）（520μg/ mL），而S21也可以耐受六价Cr（VI）（340μg/ mL）。同样，两种细菌都能够耐受其他金属，例如Hg ²⁺（40μg/ mL），Cu ²⁺（30μg/ mL），Ni ²⁺（60μg/ mL），Zn ²⁺（40μg/ mL）和Pb ²⁺（30μg/ mL）。在初始浓度为50μg/ mL时，V45和S21可以降低Cr（VI），分别达到86.42％和97.34％。在优化实验中，降低Cr（VI）的最佳温度显示为35°C，pH 7，持续96 h。V45降低六价Cr（VI）时，Cu ²⁺和Na ^+的出现略有增加，而分离株S21对Cu 2 ⁺，Mn ²⁺和Na ⁺表现出相同的作用。FTIR光谱证实，生物量中的羧酸盐和氨基缀合物在Cr（VI）的生物还原中非常复杂。此外，SEM图像显示了两种细菌细胞周围Cr（VI）的积累。从SEM-EDS光谱学可以明显看出其他元素的出现。这项研究表明制革厂沉积物中的原生细菌种群（V45和S21）具有还原Cr（VI）化合物的能力。

图形概要