National Centre for Antarctic and Ocean Research, Headland Sada, Vasco-da-Gama, Goa, India.
School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala, India.
J Basic Microbiol. 2018 May;58(5):390-402. doi: 10.1002/jobm.201700580. Epub 2018 Mar 13.
Mn-oxidizing potential of two metal-tolerant bacterial strains - Halomonas meridiana and Marinobacter algicola isolated from the South West Indian Ridge waters were compared at varying concentrations of Mn (II), i.e., 1, 10, and 100 μmol and mmol L . Accompanying changes in their morphology and metabolism were also determined. At concentrations >1 mmol L Mn (II), Mn-oxidizing potential of M. algicola was 2-7 times greater than that of H. meridiana. Scanning electron microscopy revealed that exposure to elevated metal content prompted bacterial cells especially those of M. algicola to been enveloped in exopolymeric material and form aggregates. Energy dispersive spectrometric analysis showed that exopolymeric material acts as a nucleation site for Mn deposition and oxide formation which occurs in the form of microspherical aggregates. These features show striking resemblance to biogenically produced Fe-Mn oxide deposits from Lau Basin. Surprisingly, diffractograms of auto-oxidized and bacterially formed Mn-oxide showed similarities to the hydrothermal vein mineral Rhodochrosite indicating that it can also be produced biotically. Elongation of cells by up to 4× the original size and distortion in cell shape were evident at Mn (II) concentrations >100 μmol L . Marked differences in C-substrate utilization by the test strains were also observed in presence of Mn (II). A shift in use of substrates that are readily available in oceanic waters like N-acetyl-d-glucosamine to those that can be used under changing redox conditions (d-cellobiose) or in the presence of metal ions (d-arabinose, l-asparagine) were observed. These findings highlight the significant role of autochthonous bacteria in transforming reduced metal ions and aiding in the formation of metal oxides. Under natural or laboratory conditions, the mode of bacterially generated Mn-oxide tends to remain the same.
从西南印度洋海水中分离得到的耐金属菌株——盐单胞菌（Halomonas meridiana）和海杆菌（Marinobacter algicola）的锰氧化能力在不同浓度的 Mn（II）（即 1、10 和 100 μmol 和 mmol·L-1）下进行了比较。同时还测定了它们形态和代谢的伴随变化。在浓度 >1 mmol·L-1 的 Mn（II）下，海杆菌的锰氧化能力是盐单胞菌的 2-7 倍。扫描电子显微镜显示，暴露于高金属含量会促使细菌细胞，特别是海杆菌，被包裹在胞外聚合物物质中并形成聚集体。能谱分析表明，胞外聚合物物质是 Mn 沉积和氧化物形成的成核位点，这些氧化物以微球形聚集体的形式存在。这些特征与劳盆地生物成因的 Fe-Mn 氧化物沉积物非常相似。令人惊讶的是，自动氧化和细菌形成的 Mn 氧化物的衍射图与热液脉矿物菱锰矿相似，表明它也可以生物合成。在 Mn（II）浓度 >100 μmol·L-1 时，细胞长度可延长至原始长度的 4 倍，细胞形状发生扭曲。在 Mn（II）存在下，测试菌株对 C 底物的利用也存在明显差异。观察到对海洋中易利用的底物（如 N-乙酰-d-葡萄糖胺）的利用向那些可在氧化还原条件变化下利用的底物（如 d-纤维二糖）或在金属离子存在下利用的底物（如 d-阿拉伯糖、l-天冬酰胺）的转移。这些发现强调了自生细菌在转化还原态金属离子和促进金属氧化物形成方面的重要作用。在自然或实验室条件下，细菌生成的 Mn-氧化物的模式往往保持不变。
