Wang Mengxiao, Ma Jingxuan, Wang Xuewei, Wang Zhijun, Tang Lingyi, Chen Haoming, Li Zhen
College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China.
School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China.
Appl Microbiol Biotechnol. 2020 Dec;104(23):10181-10190. doi: 10.1007/s00253-020-10952-x. Epub 2020 Oct 12.
The red yeast (Rhodotorula mucilaginosa: Rho) has abundant extracellular polymeric substances (EPS) and intracellular vesicles (Ves). This study explored the mechanisms of Rho to resist Cu toxicity from extracellular to intracellular, i.e., EPS, membrane, and Ves. The Cu concentrations were set from 0 to 200 mg/L. In contrast to other heavy metals (e.g., Pb), low Cu stress has no evident stimulation to EPS production. In particular, GSH content in EPS did not show significant changes. The Cu removal was decreased from ~ 35 to ~ 0% as Cu stress raised from 0 to 200 mg/L, which confirmed the low binding of Cu cations to EPS. Moreover, redox peaks at - 0.35 V (reduction) and - 0.02 V (oxidation) in EPS were observed based on electrochemical analysis. Subsequently, the potential Haber-Weiss reaction in EPS lowered fungal ability to shield against the Cu toxicity. Then, the contrast of Cu concentration between the extracellular and intracellular regions was enlarged. Moreover, the thickness of cell membrane decreased from 450 to 116 nm during the elevation of Cu stress. These accelerated the transport of Cu cations into intracellular, but the redox reaction in both cell membrane and intracellular region was limited. Under transmission electron microscopy, the intracellular Ves showed evident sorption of Cu cations (100 mg/L). However, the Ves started to deform and gradually lost their activity at 200 mg/L. Therefore, this study successfully elucidated the correlated extracellular and intracellular mechanisms of metal detoxification by yeast. KEY POINTS: •This study provides a comprehensive explanation for the invasion of Cu into fungal (Rhodotorula mucilaginosa) cells based on microbial physiological and biochemical analysis, electrochemical analysis, and transmitted electron microscopy. •Cu nanoparticles are involved in redox reactions in the EPS, thus greatly reducing the prophase protection for fungal cells by EPS. •At 200 mg/L Cu stress, deformation of cell membrane intensifies the contrast of Cu concentrations between extra- and intracellular regions. This further suppresses the transportation of Cu by intracellular vesicles. Graphical abstract.
红酵母（黏液红酵母：Rho）具有丰富的胞外聚合物（EPS）和细胞内囊泡（Ves）。本研究探讨了Rho从细胞外到细胞内抵抗铜毒性的机制，即EPS、细胞膜和Ves。铜浓度设定为0至200mg/L。与其他重金属（如铅）相比，低铜胁迫对EPS产生没有明显刺激。特别是，EPS中的谷胱甘肽含量没有显著变化。随着铜胁迫从0升高到200mg/L，铜去除率从约35%降至约0%，这证实了铜阳离子与EPS的低结合性。此外，基于电化学分析，在EPS中观察到-0.35V（还原）和-0.02V（氧化）的氧化还原峰。随后，EPS中潜在的哈伯-维希反应降低了真菌抵御铜毒性的能力。然后，细胞外和细胞内区域之间的铜浓度差异增大。此外，在铜胁迫升高期间，细胞膜厚度从450nm降至116nm。这些加速了铜阳离子向细胞内的运输，但细胞膜和细胞内区域的氧化还原反应受到限制。在透射电子显微镜下，细胞内囊泡显示出对铜阳离子（100mg/L）的明显吸附。然而，在200mg/L时，囊泡开始变形并逐渐失去活性。因此，本研究成功阐明了酵母进行金属解毒的相关细胞外和细胞内机制。要点：•本研究基于微生物生理生化分析、电化学分析和透射电子显微镜，对铜侵入真菌（黏液红酵母）细胞提供了全面解释。•铜纳米颗粒参与EPS中的氧化还原反应，从而大大降低了EPS对真菌细胞的前期保护作用。•在200mg/L铜胁迫下，细胞膜变形加剧了细胞外和细胞内区域铜浓度的差异。这进一步抑制了细胞内囊泡对铜的运输。图形摘要。
