Acharya Celin, Chandwadkar Pallavi, Nayak Chandrani
Molecular Biology Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
Homi Bhabha National Institute, Anushakti Nagar, Mumbai, India.
Appl Environ Microbiol. 2017 Apr 17;83(9). doi: 10.1128/AEM.03356-16. Print 2017 May 1.
Reports on interactions between cyanobacteria and uranyl carbonate are rare. Here, we present an interesting succession of the metabolic responses employed by a marine, filamentous, diazotrophic cyanobacterium, for its survival following prolonged exposure to uranyl carbonate extending up to 384 h at pH 7.8 under phosphate-limited conditions. The cells sequestered uranium (U) within polyphosphates on initial exposure to 100 μM uranyl carbonate for 24 to 28 h. Further incubation until 120 h resulted in (i) significant degradation of cellular polyphosphates causing extensive chlorosis and cell lysis, (ii) akinete differentiation followed by (iii) extracellular uranyl precipitation. X-ray diffraction (XRD) analysis, fluorescence spectroscopy, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy established the identity of the bioprecipitated uranium as a U(VI) autunite-type mineral, which settled at the bottom of the vessel. Surprisingly, cells resurfaced as small green flakes typical of actively growing colonies on top of the test solutions within 192 to 240 h of U exposure. A consolidated investigation using kinetics, microscopy, and physiological and biochemical analyses suggested a role of inducible alkaline phosphatase activity of cell aggregates/akinetes in facilitating the germination of akinetes leading to substantial regeneration of by 384 h of uranyl incubation. The biomineralized uranium appeared to be stable following cell regeneration. Altogether, our results reveal novel insights into the survival mechanism adopted by to resist sustained uranium toxicity under phosphate-limited oxic conditions. Long-term effects of uranyl exposure in cyanobacteria under oxic phosphate-limited conditions have been inadequately explored. We conducted a comprehensive examination of the metabolic responses displayed by a marine cyanobacterium, , to cope with prolonged exposure to uranyl carbonate at pH 7.8 under phosphate limitation. Our results highlight distinct adaptive mechanisms harbored by this cyanobacterium that enabled its natural regeneration following extensive cell lysis and uranium biomineralization under sustained uranium exposure. Such complex interactions between environmental microbes such as and uranium over a broader time range advance our understanding on the impact of microbial processes on uranium biogeochemistry.
关于蓝细菌与碳酸铀酰之间相互作用的报道很少。在此，我们展示了一种海洋丝状固氮蓝细菌在磷酸盐限制条件下，于pH 7.8环境中长时间暴露于碳酸铀酰长达384小时后，为求生存而采取的一系列有趣的代谢反应。细胞在最初暴露于100 μM碳酸铀酰24至28小时后，将铀（U）螯合在多磷酸盐中。进一步孵育至120小时导致：（i）细胞内多磷酸盐显著降解，引起广泛的褪绿和细胞裂解；（ii）厚壁孢子分化，随后（iii）细胞外碳酸铀酰沉淀。X射线衍射（XRD）分析、荧光光谱、X射线吸收近边结构（XANES）和扩展X射线吸收精细结构（EXAFS）光谱确定了生物沉淀铀为U(VI)钙铀云母型矿物，其沉淀在容器底部。令人惊讶的是，在铀暴露192至240小时内，细胞重新出现在测试溶液顶部，呈典型的活跃生长菌落的小绿色薄片。一项综合运用动力学、显微镜以及生理生化分析的研究表明，细胞聚集体/厚壁孢子的诱导碱性磷酸酶活性在促进厚壁孢子萌发方面发挥了作用，导致在铀酰孵育384小时后大量再生。细胞再生后，生物矿化的铀似乎很稳定。总之，我们的结果揭示了该蓝细菌在磷酸盐限制的有氧条件下抵抗持续铀毒性所采用的生存机制的新见解。在有氧磷酸盐限制条件下，铀酰暴露对蓝细菌的长期影响尚未得到充分研究。我们对一种海洋蓝细菌在磷酸盐限制下，于pH 7.8环境中长时间暴露于碳酸铀酰时所表现出的代谢反应进行了全面研究。我们的结果突出了这种蓝细菌所具有的独特适应机制，使其在持续铀暴露下经历广泛的细胞裂解和铀生物矿化后能够自然再生。像这种环境微生物与铀在更广泛时间范围内的复杂相互作用，推动了我们对微生物过程对铀生物地球化学影响的理解。
