The goal of the present work was to investigate the physicochemical and radiochemical conditions and the composition of the microbial community in the groundwater of a suspended surface repository for radioactive waste (Russia) and to determine the possibility of in situ groundwater bioremediation by removal of nitrate ions. Groundwater in the repository area (10-m depth) had elevated concentrations of strontium, tritium, nitrate, sulfate, and bicarbonate ions. High-throughput sequencing of the V3–V4/V4 region of the 16S rRNA gene revealed the presence of members of the phyla Proteobacteria (genera Acidovorax, Simplicispira, Thermomonas, Thiobacillus, Pseudomonas, Brevundimonas, and uncultured Oxalobacteraceae), Firmicutes (genera Bacillus and Paenibacillus), and Actinobacteria (Candidatus Planktophila, Gaiella). Canonical correspondence analysis suggested that major contaminant – nitrate, uranium, and sulfate shaped the composition of groundwater microbial community. Groundwater samples contained culturable aerobic organotrophic, as well as anaerobic fermenting, iron-reducing, and denitrifying bacteria. Pure cultures of 33 bacterial strains belonging to 15 genera were isolated. Members of the genera Pseudomonas, Rhizobium, Cupriavidus, Shewanella, Ensifer, and Thermomonas reduced nitrate to nitrite and/or dinitrogen. Application of specific primers revealed the nirS and nirK genes encoding nitrite reductases in bacteria of the genera Pseudomonas, Rhizobium, and Ensifer. Nitrate reduction by pure bacterial cultures resulted in decreased ambient Eh. Among the organic substrates tested, sodium acetate and milk whey were the best for stimulation of denitrification by the microcosms with groundwater microorganisms. Injection of these substrates into the subterranean horizon (single-well push-pull test) resulted in temporary removal of nitrate ions in the area of the suspended radioactive waste repository and confirmed the possibility for in situ application of this method for bioremediation.

Biomimetic nanomaterials (BNMs) are functional materials containing nanoscale components and having structural and technological similarities to natural (biogenic) prototypes. Despite the fact that biomimetic approaches in materials technology have been used since the second half of the 20th century, BNMs are still at the forefront of materials science. This review considered a general classification of such nanomaterials according to the characteristic features of natural analogues that are reproduced in the preparation of BNMs, including biomimetic structure, biomimetic synthesis, and the inclusion of biogenic components. BNMs containing magnetic, metal, or metal oxide organic and ceramic structural elements (including their various combinations) were considered separately. The BNMs under consideration were analyzed according to the declared areas of application, which included tooth and bone reconstruction, magnetic and infrared hyperthermia, chemo- and immunotherapy, the development of new drugs for targeted therapy, antibacterial and anti-inflammatory therapy, and bioimaging. In conclusion, the authors’ point of view is given about the prospects for the development of this scientific area associated with the use of native, genetically modified, or completely artificial phospholipid membranes, which allow combining the physicochemical and biological properties of biogenic prototypes with high biocompatibility, economic availability, and scalability of fully synthetic nanomaterials.

Magnetotactic bacteria (MTB) are prokaryotes that possess genes for the synthesis of membrane-bounded crystals of magnetite or greigite, called magnetosomes. Despite over half a century of studying MTB, only about 60 genomes have been sequenced. Most belong to Proteobacteria, with a minority affiliated with the Nitrospirae, Omnitrophica, Planctomycetes, and Latescibacteria. Due to the scanty information available regarding MTB phylogenetic diversity, little is known about their ecology, evolution and about the magnetosome biomineralization process. This study presents a large-scale search of magnetosome biomineralization genes and reveals 38 new MTB genomes. Several of these genomes were detected in the phyla Elusimicrobia, Candidatus Hydrogenedentes, and Nitrospinae, where magnetotactic representatives have not previously been reported. Analysis of the obtained putative magnetosome biomineralization genes revealed a monophyletic origin capable of putative greigite magnetosome synthesis. The ecological distributions of the reconstructed MTB genomes were also analyzed and several patterns were identified. These data suggest that open databases are an excellent source for obtaining new information of interest.

Three strains of helical-shaped, magnetotactic bacteria, SO-1T, SP-1T and BB-1T, were isolated from freshwater sediments collected from three distinct points of European Russia. Phylogenetic analysis showed that the strains belong to the genus Magnetospirillum. Strains SO-1T and SP-1T showed the highest 16S rRNA gene sequence similarities with Magnetospirillum magnetotacticum MS-1T (99.3% and 98.1% respectively), strain BB-1T with Magnetospirillum gryphiswaldense MSR-1T (97.3%). The tree based on the concatenated amino acid sequences of the MamA, B, K, M, O, P, Q and T proteins which are involved in magnetosome formation was congruent with the tree based on the 16S rRNA gene sequences. The genomic G+C contents of the strains SO-1T, SP-1T and BB-1T were 65.9, 63.0 and 65.2 mol% respectively. As major fatty acids, C18:1ω9, C16:1ω7c, C16:0 and C18:0 were detected. DDH values between the strains and their closest relatives in the genus Magnetospirillum were less than 51.7±2.3%. In contrast to M. magnetotacticum MS-1T, the strains could utilize butyrate and propionate, strains SO-1T and BB-1T could utilize glycerol. Strain SP-1T showed strictly microaerophilic growth, whereas strains SO-1T and BB-1T were more tolerant to oxygen. The results of DDH and physiological tests allowed genotypic and phenotypic differentiation of the strains from each other as well as from the two validly published Magnetospirillum species. Therefore the strains represent the new species for which were proposed the names Magnetospirillum caucaseum sp. nov., type strain SO-1T (=DSM28995T=VKM B-2936T), Magnetospirillum marisnigri sp. nov., type strain SP-1T (=DSM29006T=VKM B-2938T), and Magnetospirillum moscoviense sp.nov., type strain BB-1T (=DSM29455T=VKM B-2939T).

Magnetotactic bacteria (MTB) belong to several phyla. This class of microorganisms exhibits the ability of magneto-aerotaxis. MTB synthesize biominerals in organelle-like structures called magnetosomes, which contain single-domain crystals of magnetite (Fe₃O₄) or greigite (Fe₃S₄) characterized by a high degree of structural and compositional perfection. Magnetosomes from dead MTB could be preserved in sediments (called fossil magnetosomes or magnetofossils). Under certain conditions, magnetofossils are capable of retaining their remanence for millions of years. This accounts for the growing interest in MTB and magnetofossils in paleo- and rock magnetism and in a wider field of biogeoscience. At the same time, high biocompatibility of magnetosomes makes possible their potential use in biomedical applications, including magnetic resonance imaging, hyperthermia, magnetically guided drug delivery, and immunomagnetic analysis. In this review, we attempt to summarize the current state of the art in the field of MTB research and applications.