黄河下游支流铬污染沉积物中耐Cr(Ⅵ)真菌的分离及转化机制

Isolation and transformation mechanism of Cr(VI)-tolerant fungi from Cr-contaminated sediments in the downstream tributary of the Yellow River

摘要:

【背景】 黄河下游支流——蟒河因长期受重金属废水排放的影响，其沉积物存在以铬污染为主的重金属复合污染，污染区形成独特的微生物群落。【目的】 从该污染区的沉积物中筛选耐受和转化高浓度Cr(Ⅵ)污染的真菌，并对其Cr(Ⅵ)转化能力和机理进行探究。【方法】 采用梯度培养法进行耐受和转化高浓度Cr(Ⅵ)污染真菌的筛选；采用形态学观察和ITS序列分析的方法进行菌种鉴定；通过菌株不同组分对Cr(Ⅵ)的还原能力、扫描电镜(scanning electron microscope, SEM)、傅里叶变换红外光谱(Fourier transform infrared spectroscopy, FTIR)、X射线光电子能谱(X-ray photoelectron spectroscopy, XPS)及X射线衍射(X-ray diffraction, XRD)对菌株转化Cr(Ⅵ)的机理进行探究。【结果】 筛选得到2株真菌p18和p20耐受1 000 mg/L Cr(Ⅵ)，经鉴定分别为云南木霉(Trichoderma yunnanense)和环形镰刀菌(Fusarium annulatum)。2株菌在100 mg/L Cr(Ⅵ)培养120 h的Cr(Ⅵ)去除率分别达到79.40%和63.48%，Cr(Ⅵ)还原率分别为73.55%和50.94%；对积累铬能力的测定发现，500 mg/L Cr(Ⅵ)条件下p18和p20每克菌体干重积累铬含量达到最大，分别为10.84 mg和6.98 mg。通过SEM菌体表征分析发现铬处理后的菌株p18和p20菌体表面附着铬颗粒；FTIR测定表明氨基、羟基、羰基、C-H和酰胺基参与了铬的吸附；通过XPS和XRD分析证实了菌体转化Cr(Ⅵ)生成Cr(OH)₃，处于无定形和晶体之间。进一步测定菌体不同组分对Cr(Ⅵ)的还原能力，结果表明Cr(Ⅵ)还原物质主要位于胞外分泌物(extracellular secretion)。【结论】 筛选得到的2株高耐Cr(Ⅵ)真菌T. yunnanense、F. annulatum对Cr(Ⅵ)具有高效的转化能力，为河流长期污染下重金属转化过程和污染修复提供依据。

Abstract:

[Background] The Manghe River, a downstream tributary of the Yellow River, suffers from heavy metal-containing wastewater discharge over a long period of time, and its sediments are characterized by the presence of heavy metal composite pollution dominated by chromium contamination, with the formation of a unique microbial community in the contaminated area. [Objective] To screen the fungi capable of tolerating and transforming high concentrations of Cr(VI) in the sediments of the contaminated area and explore the Cr(VI) transformation ability and mechanism. [Methods] The fungi capable of tolerating and transforming high concentrations of Cr(VI) were screened by the gradient culture method and identified by morphological observation and ITS sequencing. The mechanism of Cr(VI) transformation by the strains was investigated based on the reduction ability of different components of the strains, scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). [Results] Two fungal strains p18 and p20 tolerant to 1 000 mg/L Cr(VI) were isolated and identified as Trichoderma yunnanense and Fusarium annulatum, respectively. The two strains showed the Cr(VI) removal rates of 79.40% and 63.48% and the Cr(VI) reduction rates of 73.55% and 50.94%, respectively, after being cultured with 100 mg/L Cr(VI) for 120 h. In the medium with 500 mg/L Cr(VI), p18 and p20 accumulated the highest amounts of Cr per gram of dry mycelia, which reached 10.84 mg and 6.98 mg, respectively. SEM revealed that the surfaces of p18 and p20 cells were adorned with Cr particles after exposure to Cr treatment. FTIR indicated that -NH, -OH, C=O, C-H, and -CONH₂ were involved in the adsorption of Cr. XPS and XRD confirmed that the strains transformed Cr(VI) into Cr(OH)₃, which existed in an intermediate state between amorphous and crystalline forms. The predominant substances responsible for Cr(VI) reduction were the extracellular secretion of the two strains. [Conclusion] The two highly Cr(VI)-tolerant fungal strains, T. yunnanense and F. annulatum, demonstrate efficient transformation of Cr(VI), which provide a basis for the heavy metal transformation and remediation of the river suffering from long-term contamination.