Recover vigorous cells of Magnetospirillum magneticum AMB-1 by capillary magnetic separation

Cultivable magnetotactic bacteria(MTB) in laboratory can provide sufficient samples for molecular microbiological and magnetic studies.However,a cold-stored MTB strain,such as Magnetospirillum magneticum AMB-1,often loses its ability to synthesize magnetosomes and consequently fails to sense the external magnetic field.It is therefore important to quickly recover vigorous bacteria cells that highly capable of magnetosome producing.In this study,a modified capillary magnetic separation system was designed to recover a deteriorating strain of Magnetospirillum magneticum AMB-1 that long-term cold-stored in a refrigerator.The results show that all cells obtained after a 3-cycle treatment were vigorous and had the ability to produce magnetosomes.Moreover,the 3rd-cycle recovered cells were able to form more magnetosome crystals.Compared with the colony formation method,this new method is time-saving,easily operated,and more efficient for recovering vigorous MTB cells.

Metamorphosis of Magnetospirillum magneticum AMB-1 cells

Magnetospirillum magneticum strain AMB-1 belongs to the family of magnetotactic bacteria. It possesses a magnetosome chain aligning, with the assistance of cytoskeleton filaments MamK, along the long axis of the spiral cells. Most fresh M. magneticum AMB-1 cells exhibit spiral morphology. In addition, other cell shapes such as curved and spherical were also observed in this organism. Interestingly, the spherical cell shape increased steadily with prolonged incubation time. As the actin-like cytoskeleton protein MreB is involved in maintenance of cell shapes in rod-shaped bacteria such as Escherichia coli and Bacillus subtilis, the correlation between MreB protein levels and cell shape was investigated in this study. Immunoblotting analysis showed that the quantity of MreB decreased when the cell shape changed along with incubation time. As an internal control, the quantity of MamA was not obviously changed under the same conditions. Cell shape directs cell-wall synthesis during growth and division. MreB is required for maintaining the cell shape. Thus, MreB might play an essential role in maintaining the spiral shape of M. magneticum AMB-1 cells.

Electroactivity of the magnetotactic bacteria Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1

Magnetotactic bacteria reside in sediments and stratified water columns.They are named after their ability to synthesize internal magnetic particles that allow them to align and swim along the Earth’s magnetic field lines.Here,we show that two magnetotactic species,Magnetospirillum magneticum strain AMB-1 and Magnetospirillum gryphiswaldense strain MSR-1,are electroactive.Both M.magneticum and M.gryphiswaldense were able to generate current in microbial fuel cells with maximum power densities of 27 and 11μW/m^(2),respectively.In the presence of the electron shuttle resazurin both species were able to reduce the crystalline iron oxide hematite(Fe_(2)O_(3)).In addition,M.magneticum could reduce poorly crystalline iron oxide(FeOOH).Our study adds M.magneticum and M.gryphiswaldense to the growing list of known electroactive bacteria,and implies that electroactivity might be common for bacteria within the Magnetospirillum genus.

A comparative study of magnetic properties between whole cells and isolated magnetosomes of Magnetospirillum magneticum AMB-1

The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials in biotechnological and biomedical applications. We carried out magnetic and electron transmission microscopy analyses of fresh Magnetospirillum magneticum AMB-1 whole cells and isolated magnetosomes. Results revealed that AMB-1 synthesized single-domain magnetite magneto-somes, which are arranged in the form of linear fragmental chain. The distinct differences of magnetic properties between these two samples can be faithfully interpreted in terms of spatial arrangement of magnetosomes and magnetostatic interaction. For the whole cells, the strong intra-chain interactions and weak inter-chain interactions generate behaviors of non-interacting uniaxial single-domain particles. Its δ-ratio is 3.0 and passes the Moskowitz test. In contrast, the isolated magnetosome sample has reduced values of coercivity and δ-ratio (1.5), due to increasing three-dimensional magnetostatic interactions and collapse of magneto-some chains. These observations provide useful insights into applications of the biogenic magnetite (magnetosomes) in magnetic nano-materials and magnetofossils in the paleomagnetic and environmental magnetism.

趋磁细菌的电化学活性研究

采用循环伏安和计时电流等电化学手段研究了趋磁细菌(Magnetospirillum magneticum AMB-1)的电化学活性.通过对比不同培养条件下的循环伏安曲线可知,培养3 d时的菌体具有较强的电化学活性,其氧化峰出现在0.1 V处,还原峰出现在-0.2 V处;溶解氧能够改变氧化峰的峰电位(0 V),并形成新的还原峰(-0.3 V);磁小体的生成则严重抑制趋磁细菌的胞外电子传递过程.实验结果表明,磁小体的形成与趋磁细菌的胞外电子传递有关.

趋磁螺菌AMB-l磁小体合成相关基因的克隆及功能分析

为了更清楚的了解趋磁螺菌产磁小体的合成机理和调节途径,用Tn5转座子诱变的方法筛选得到了2株磁小体合成降低的突变株,并克隆了突变株中被插入失活的基因,分别为编码ABC型Fe3+转移系统中的离子结合蛋白的amb3385基因和功能未知的amb3672基因.互补实验表明携带amb3385和amb3672基因的广宿主载体可以不同程度地恢复突变株中磁小体的合成,证明了D.Schüler关于磁小体合成假说的第一个步骤,即Fe3+从胞外向经由Fe3+转运蛋白运输至了胞内.由于amb3672基因比对时未发现特殊相似基因,其功能尚需进一步研究.

趋磁菌AMB-1超氧化物歧化酶Fe-SOD在大肠杆菌中的表达及生理活性研究

超氧化物歧化酶(SOD)可以减轻超阳阴离子O_2^-对细胞的毒害作用,提高菌体的抗氧化能力,从而改善菌株的生理状态。利用PCR技术,将趋磁菌AMB-1的超氧化物歧化酶基因fesod克隆至原核表达载体pET-20b(+),并在E.coli BL21(DE3)有效表达。重组菌株BL21(DE3)/(pET-20b-fesod-histag)在0.6 mmol/L IPTG诱导浓度下进行发酵培养,在生长前期2-14 h生长速率优于对照组E.coli BL21(DE3)/(pET-20b)。通过亲和层析柱纯化后,重组酶蛋白纯度达电泳均一,超氧化物歧化酶fesod活性最适作用温度为25℃,在25℃和45℃下酶热稳定较好,pH4.2-8.2之间酶活力稳定。趋磁菌AMB-1来源的Fe-SOD作为一种抗氧化酶,在大肠杆菌中的有效表达从一定程度上改善了宿主菌的生长情况。

趋磁细菌AMB-1生物矿化相关蛋白Mms6参与磁小体的合成

【目的】研究趋磁细菌AMB-1生物矿化相关蛋白Mms6与磁小体合成的关系。【方法】在液体静置培养条件和好氧条件下对AMB-1进行培养,分析基因mms6在不同培养条件下转录水平的变化;对基因mms6进行基因敲除,分析突变株的生长和产磁变化。【结果】基因mms6的转录水平随着磁小体的合成逐渐升高;mms6的突变导致菌株在液体静置培养条件下趋磁性降低约50%,但不会影响菌株的生长水平。【结论】基因mms6参与了趋磁细菌AMB-1胞内磁小体的合成。