Isolation of Thiomonas thermosulfatus Strain 51, a Species Capable of Coupling Biogenic Pyritization with Chemiosmotic Energy Transduction

The precipitation of iron sulfides potentially offers enough energy and reducing power to sustain life but organisms harnessing this reaction have not to our knowledge been previously described. We isolated a bacterial strain, capable of forming the iron sulfide minerals troilite (FeS), greigite (Fe₃S₄), and pyrite (FeS₂), from subsurface, microbial mats in Mangalia, Romania. This strain, most closely related to strains of Thiomonas sp., forms pyrite only if the redox conditions remain negative (< ?60 mV), sulfides are provided continually (≈1 mM), and the concentration of iron remains low (≤ 0.08 mM) but constant. Pyrite formation by this microbial strain is proposed as an example of biologically controlled mineralization because it is controlled by uncouplers of oxidative phosphorylation, it is larger in living than in dead cells, it is additive (controlled less by the amount of cell surfaces and more by reagents), and it results in the formation of ATP. This study indicates that precipitation and crystal formation can represent an energy resource for life and provides support for the “iron-sulfide world hypothesis” regarding the early evolution of life on Earth.     

多细胞趋磁原核生物研究进展

多细胞趋磁原核生物指一类由含有磁小体的革兰氏阴性原核细胞聚集而成的球形或者卵球形细胞聚集体,一般由745个细胞组成,直径在223μm之间,它们可在地磁场或外加磁场中沿磁力线定位并做定向运动。通过对巴西潟湖、美国盐湖、德国和法国海岸带花瓣型MMPs以及最近对中国青岛海域潮间带菠萝型MMPs研究结果的总结,分别从MMPs的生物学特征、细胞内容物以及生态学分布及分类地位等方面的研究进行综述,并对未来研究方向进行一定的展望。     

Common ancestry of iron oxide- and iron-sulfide-based biomineralization in magnetotactic bacteria

Magnetosomes are prokaryotic organelles produced by magnetotactic bacteria that consist of nanometer-sized magnetite (Fe₃O₄) or/and greigite (Fe₃S₄) magnetic crystals enveloped by a lipid bilayer membrane. In magnetite-producing magnetotactic bacteria, proteins present in the magnetosome membrane modulate biomineralization of the magnetite crystal. In these microorganisms, genes that encode for magnetosome membrane proteins as well as genes involved in the construction of the magnetite magnetosome chain, the mam and mms genes, are organized within a genomic island. However, partially because there are presently no greigite-producing magnetotactic bacteria in pure culture, little is known regarding the greigite biomineralization process in these organisms including whether similar genes are involved in the process. Here using culture-independent techniques, we now show that mam genes involved in the production of magnetite magnetosomes are also present in greigite-producing magnetotactic bacteria. This finding suggest that the biomineralization of magnetite and greigite did not have evolve independently (that is, magnetotaxis is polyphyletic) as once suggested. Instead, results presented here are consistent with a model in which the ability to biomineralize magnetosomes and the possession of the mam genes was acquired by bacteria from a common ancestor, that is, the magnetotactic trait is monophyletic.     

Geochemical Characteristics Related to the Gregite-Producing Multicellular Magnetotactic Prokaryote Candidatus Magnetoglobus multicellularis in a Hypersaline Lagoon

We studied the geochemical properties of sediment layers where the gregite-producing multicellular magnetotactic prokaryote Candidatus Magnetoglobus multicellularis exists. The ratio of iron and bioavailable sulfur concentrations regulates the population density of this microorganism. The population density can reach 8.5 × 10² cells/cm³ at an iron to sulfur ratio of 0.5. In iron- and sulfur-rich environments, microorganisms concentrated in the upper region of the oxic-anoxic zone, following an increasing nitrogen gradient with a lower isotopic ¹⁵N/¹⁴N ratio. Candidatus Magnetoglobus multicellularis prefers environmental conditions that favor the biomineralization of greigite, but in situations where the nutrient availability is low, it moves to more suitable sites.