Instituto de Microbiologia Paulo de Góes, Departamento de Microbiologia Geral, Universidade Federal do Rio de Janeiro, 21941-902, Rio de Janeiro, RJ, Brazil.
Instituto de Biologia, Departamento de Botânica, Universidade Federal do Rio de Janeiro, 21941-902, Rio de Janeiro, RJ, Brazil.
Environ Microbiol. 2018 Jul;20(7):2615-2624. doi: 10.1111/1462-2920.14286.
Magnetotactic bacteria (MTB) comprise a group of motile microorganisms common in most mesothermal aquatic habitats with pH values around neutrality. However, during the last two decades, a number of MTB from extreme environments have been characterized including: cultured alkaliphilic strains belonging to the Deltaproteobacteria class of the Proteobacteria phylum; uncultured moderately thermophilic strains belonging to the Nitrospirae phylum; cultured and uncultured moderately halophilic or strongly halotolerant bacteria affiliated with the Deltaproteobacteria and Gammaproteobacteria classes and an uncultured psychrophilic species belonging to the Alphaproteobacteria class. Here, we used culture-independent techniques to characterize MTB from an acidic freshwater lagoon in Brazil (pH ∼ 4.4). MTB morphotypes found in this acidic lagoon included cocci, rods, spirilla and vibrioid cells. Magnetite (Fe O ) was the only mineral identified in magnetosomes of these MTB while magnetite magnetosome crystal morphologies within the different MTB cells included cuboctahedral (present in spirilla), elongated prismatic (present in cocci and vibrios) and bullet-shaped (present in rod-shaped cells). Intracellular pH measurements using fluorescent dyes showed that the cytoplasmic pH was close to neutral in most MTB cells and acidic in some intracellular granules. Based on 16S rRNA gene phylogenetic analyses, some of the retrieved gene sequences belonged to the genus Herbaspirillum within the Betaproteobacteria class of the Proteobacteria phylum. Fluorescent in situ hybridization using a Herbaspirillum-specific probe hybridized with vibrioid MTB in magnetically-enriched samples. Transmission electron microscopy of the Herbaspirillum-like MTB revealed the presence of many intracellular granules and a single chain of elongated prismatic magnetite magnetosomes. Diverse populations of MTB have not seemed to have been described in detail in an acid environment. In addition, this is the first report of an MTB phylogenetically affiliated with Betaproteobacteria class.
趋磁细菌（MTB）是一类常见于大多数中性 pH 值的中温热水栖息地的运动微生物。然而，在过去的二十年中，已经描述了许多来自极端环境的 MTB，包括：属于变形菌门的δ-变形菌纲的培养的嗜碱性菌株；属于硝化螺旋菌门的未培养的中温菌株；属于δ-变形菌纲和γ-变形菌纲的培养和未培养的中度嗜盐或强耐盐细菌以及属于α-变形菌纲的未培养的嗜冷物种。在这里，我们使用非培养技术来描述巴西一个酸性淡水泻湖（pH ∼ 4.4）中的 MTB。在这个酸性泻湖中发现的 MTB 形态包括球菌、杆菌、螺旋体和弧菌。这些 MTB 的磁小体中只鉴定出磁铁矿（Fe3O4），而不同 MTB 细胞中的磁铁矿磁小体晶体形态包括立方八面体（存在于螺旋体中）、拉长的棱柱体（存在于球菌和弧菌中）和子弹形（存在于杆状细胞中）。使用荧光染料进行的细胞内 pH 测量表明，大多数 MTB 细胞的细胞质 pH 接近中性，而一些细胞内颗粒的 pH 呈酸性。基于 16S rRNA 基因系统发育分析，一些回收的基因序列属于β-变形菌纲的噬氢菌属。用针对噬氢菌属的特异性探针进行的荧光原位杂交与磁富集样品中的弧菌 MTB 杂交。对类似 Herbaspirillum 的 MTB 的透射电子显微镜观察显示存在许多细胞内颗粒和单链拉长的棱柱形磁铁矿磁小体。在酸性环境中似乎还没有详细描述过多样化的 MTB 种群。此外，这是首次报道与β-变形菌纲有系统发育关系的 MTB。
