Magnetite produced by magnetotactic bacteria (MTB) provides stable paleomagnetic signals because it occurs as natural single‐domain magnetic nanocrystals. MTB can also provide useful paleoenvironmental information because their crystal morphologies are associated with particular bacterial groups and the environments in which they live. However, identification of the fossil remains of MTB (i.e., magnetofossils) from ancient sediments or rocks is challenging because of their generally small sizes and because the growth, morphology, and chain assembly of magnetite within MTB are not well understood. Nanoscale characterization is, therefore, needed to understand magnetite biomineralization and to develop magnetofossils as biogeochemical proxies for paleoenvironmental reconstructions. Using advanced transmission electron microscopy, we investigated magnetite growth and chain arrangements within magnetotactic Deltaproteobacteria strain WYHR‐1, which reveals how the magnetite grows to form elongated, bullet‐shaped nanocrystals. Three crystal growth stages are recognized: (i) initial isotropic growth to produce nearly round ~20 nm particles, (ii) subsequent anisotropic growth along the [001] crystallographic direction to ~75 nm lengths and ~30–40 nm widths, and (iii) unidirectional growth along the [001] direction to ~180 nm lengths, with some growing to ~280 nm. Crystal growth and habit differ from that of magnetite produced by other known MTB strains, which indicates species‐specific biomineralization. These findings suggest that magnetite biomineralization might be much more diverse among MTB than previously thought. When characterized adequately at species level, magnetofossil crystallography, and apomorphic features are, therefore, likely to become useful proxies for ancient MTB taxonomic groups or species and for interpreting the environments in which they lived.

Summary Magnetotactic bacteria (MTB) are diverse prokaryotes that produce magnetic nanocrystals within intracellular membranes (magnetosomes). Here, we present a large‐scale analysis of diversity and magnetosome biomineralization in modern magnetotactic cocci, which are the most abundant MTB morphotypes in nature. Nineteen novel magnetotactic cocci species are identified phylogenetically and structurally at the single‐cell level. Phylogenetic analysis demonstrates that the cocci cluster into an independent branch from other Alphaproteobacteria MTB, that is, within the Etaproteobacteria class in the Proteobacteria phylum. Statistical analysis reveals species‐specific biomineralization of magnetosomal magnetite morphologies. This further confirms that magnetosome biomineralization is controlled strictly by the MTB cell and differs among species or strains. The post‐mortem remains of MTB are often preserved as magnetofossils within sediments or sedimentary rocks, yet paleobiological and geological interpretation of their fossil record remains challenging. Our results indicate that magnetofossil morphology could be a promising proxy for retrieving paleobiological information about ancient MTB.

Magnetotactic bacteria (MTB) widely inhabit the oxic-anoxic interface (OAI) of sediments and water columns, with their motility guided by geomagnetic fields (a behavior known as magnetotaxis). Beside biomineralizing membrane-enveloped magnetite or greigite nanocrystals called magnetosomes, cells of many MTB groups contain numerous sulfur globules within their cells. Here, by combining transmission electron microscopy and synchrotron-based scanning transmission X-ray microscopy, we investigated the cellular structure and chemistry of Candidatus Magnetobacterium casensis (Mcas), a giant rod-shaped MTB from the Nitrospirae phylum. We find that nitrate-storing vacuoles and linearly polymeric sulfur globules occur exclusively within some Mcas cells along with magnetosomal magnetite. Genomic prediction indicates that Mcas cells have the potential to oxidize sulfide to sulfate (i.e., S 2− → S 0 → SO 3 2− → SO 4 2−), to reduce sulfate to sulfide (i.e., SO 4 2− → SO 3 2− → S 2−), and to reduce nitrate to NH 4 + /N 2. Together with previous environmental observations, comparative genomic analysis allows us to propose a model for Mcas involving the microbial sulfur cycle across aquatic OAIs based on magnetotaxis. Via directional movement guided by geomagnetic fields, Mcas cells shuttle either upward to upper microoxic zones for sulfur oxidation and nitrate accumulation in the OAI, or downward to deeper anoxic zones for sulfur deposition by coupling sulfide oxidation and nitrate reduction. Development of magnetotaxis makes MTB an efficient bacterial shuttle for C, N, S, and Fe across aquatic OAI environments and likely contributes significantly to their global biogeochemical cycling. It also benefits cell growth and magnetosomal magnetite formation in MTB. Plain Language Summary Microbial sulfur cycling across the oxic-anoxic interface (OAI) of sediments and the water column is an important component of the global sulfur cycle. Electrons from deeper anoxic zones are transported to microoxic/oxic surface zones, which drives biogeochemical element cycling across OAIs. Vast amounts of sulfide are produced in deeper anoxic zones. This sulfide must either be taken up there or be oxidized completely in upper microoxic/oxic zones by sulfide oxidizers via several adaption strategies. We report here a new adaptation to the microbial sulfur cycle in a giant magnetotactic bacterium, Mcas. This MTB forms intracellular sulfur globules or vacuoles (possibly storing nitrate) along with magnetosomal magnetite, and its up-and-down movement within the OAI is guided by geomagnetic fields. This adaptation is beneficial for cell growth and magnetite biomineralization in Mcas, but it also makes magnetotactic bacteria efficient bacterial shuttles for C, N, S, and Fe in aquatic OAI environments.

Multi-modal pre-training models have been intensively explored to bridge vision and language in recent years. However, most of them explicitly model the cross-modal interaction between image-text pairs, by assuming that there exists strong semantic correlation between the text and image modalities. Since this strong assumption is often invalid in real-world scenarios, we choose to implicitly model the cross-modal correlation for large-scale multi-modal pretraining, which is the focus of the Chinese project 'Wen-Lan' led by our team. Specifically, with the weak correlation assumption over image-text pairs, we propose a twotower pre-training model called BriVL within the crossmodal contrastive learning framework. Unlike OpenAI CLIP that adopts a simple contrastive learning method, we devise a more advanced algorithm by adapting the latest method MoCo into the cross-modal scenario. By building a large queue-based dictionary, our BriVL can incorporate more negative samples in limited GPU resources. We further construct a large Chinese multi-source imagetext dataset called RUC-CAS-WenLan for pre-training our BriVL model. Extensive experiments demonstrate that the pre-trained BriVL model outperforms both UNITER and OpenAI CLIP on various downstream tasks.

Magnetotactic bacteria (MTB) are morphologically and phylogenetically diverse prokaryotes. They can form intracellular chain-assembled magnetite (Fe3O4) or greigite (Fe3S4) nanocrystals each enveloped by a lipid bilayer membrane called a magnetosome. Magnetotactic cocci have been found to be the most abundant morphotypes of MTB in various aquatic environments. However, knowledge on magnetosome biomineralization within magnetotactic cocci remains elusive due to small number of strains that have been cultured. By using a coordinated fluorescence and scanning electron microscopy method, we discovered a unique magnetotactic coccus strain (tentatively named SHHC-1) in brackish sediments collected from the estuary of Shihe River in Qinhuangdao city, eastern China. It phylogenetically belongs to the Alphaproteobacteria class. Transmission electron microscopy analyses reveal that SHHC-1 cells formed many magnetite-type magnetosomes organized as two bundles in each cell. Each bundle contains two parallel chains with smaller magnetosomes generally located at the ends of each chain. Unlike most magnetotactic alphaproteobacteria that generally form magnetosomes with uniform crystal morphologies, SHHC-1 magnetosomes display a more diverse variety of crystal morphology even within a single cell. Most particles have rectangular and rhomboidal projections, whilst others are triangular, or irregular. High resolution transmission electron microscopy observations coupled with morphological modeling indicate an idealized model—elongated octahedral crystals, a form composed of eight {111} faces. Furthermore, twins, multiple twins and stack dislocations are frequently observed in the SHHC-1 magnetosomes. This suggests that biomineralization of strain SHHC-1 magnetosome might be less biologically controlled than other magnetotactic alphaproteobacteria. Alternatively, SHHC-1 is more sensitive to the unfavorable environments under which it lives, or a combination of both factors may have controlled the magnetosome biomineralization process within this unique MTB.

Magnetotactic bacteria (MTB) are phylogenetically diverse prokaryotes that are able to biomineralize intracellular, magnetic chains of magnetite or greigite nanocrystals called magnetosomes. Simultaneous characterization of MTB phylogeny and biomineralization is crucial but challenging because most MTB are extremely difficult to culture. We identify a large rod, bean-like MTB (tentatively named WYHR-1) from freshwater sediments of Weiyang Lake, Xi'an, China, using a coupled fluorescence and scanning electron microscopy approach at the single-cell scale. Phylogenetic analysis of 16S rRNA gene sequences indicates that WYHR-1 is a novel genus from the Deltaproteobacteria class. Transmission electron microscope observations reveal that WYHR-1 cells contain tens of magnetite magnetosomes that are organized into a single chain bundle along the cell long axis. Mature WYHR-1 magnetosomes are bullet-shaped, straight, and elongated along the [001] direction, with a large flat end terminated by a {100} face at the base and a conical top. This crystal morphology is distinctively different from bullet-shaped magnetosomes produced by other MTB in the Deltaproteobacteria class and the Nitrospirae phylum. This indicates that WYHR-1 may have a different crystal growth process and mechanism from other species, which results from species-specific magnetosome biomineralization in MTB. IMPORTANCE Magnetotactic bacteria (MTB) represent a model system for understanding biomineralization and are also studied intensively in biogeomagnetic and paleomagnetic research. However, many uncultured MTB strains have not been identified phylogenetically or investigated structurally at the single-cell level, which limits comprehensive understanding of MTB diversity and their role in biomineralization. We have identified a novel MTB strain, WYHR-1, from a freshwater lake using a coupled fluorescence and scanning electron microscopy approach at the single-cell scale. Our analyses further indicate that strain WYHR-1 represents a novel genus from the Deltaproteobacteria class. In contrast to bullet-shaped magnetosomes produced by other MTB in the Deltaproteobacteria class and the Nitrospirae phylum, WYHR-1 magnetosomes are bullet-shaped, straight, and highly elongated along the [001] direction, are terminated by a large {100} face at their base, and have a conical top. Our findings imply that, consistent with phylogenetic diversity of MTB, bulletshaped magnetosomes have diverse crystal habits and growth patterns.

Magnetotactic bacteria (MTB) have long fascinated geologists and biologists because they biomineralize intracellular single domain (SD) magnetite crystals within magnetosomes that are generally organized into single or multiple chains. MTB remains in the geological record (magnetofossils) are ideal magnetic carriers and are used to reconstruct paleomagnetic and paleoenvironmental information. Here we studied the biomineralization and magnetic properties of magnetosomal magnetite produced by uncultured magnetotactic coccus strain THC-1, isolated from the Tanghe River, China, by combining transmission electron microscope (TEM) and rock magnetic approaches. Our results reveal that THC-1 produces hexagonal prismatic magnetite single crystals that are elongated along the [111] crystallographic direction. Most of the magnetite crystals within THC-1 are dispersed without obvious chain assembly. A whole-cell THC-1 sample yields a normal SD hysteresis loop and a Verwey transition temperature of 112 K. In contrast to MTB cells with magnetosome chain(s), THC-1 cells have a teardrop first-order reversal curve distribution that is indicative of moderate interparticle interactions. Due to the absence of a magnetosome chain, THC-1 has relatively high values of the difference between the saturation isothermal remanent magnetization (SIRM) below and above the Verwey transition temperature for field-cooled and zero field-cooled SIRM curves (δ FC , δ ZFC) and a low δ FC /δ ZFC value. Together with previous studies, our results demonstrate that some MTB species/strains can form magnetosomal magnetite without linear chain configurations. Magnetite produced by MTB has diverse magnetic properties, which are distinctive but not necessarily unique compared to other magnetite types. Therefore, combining bulk magnetic measurements and TEM observations remains necessary for identifying magnetofossils in the geological record. Plain Language Summary Magnetotactic bacteria (MTB) are intriguing because they produce magnetic nanocrystals of magnetite (Fe 3 O 4) or greigite (Fe 3 S 4) within intracellular organelles (magnetosomes) that can leave tiny magnetic fossils (magnetofossils) in the geological record. Magnetofossil identification for paleoenvironmental and paleomagnetic purposes is based heavily on knowledge of modern MTB that often organize magnetic particles into chain(s). We studied here the crystallographic and magnetic properties of uncultured magnetotactic coccus strain THC-1 in which magnetosomal magnetite particles are dispersed without obvious chain assembly. In contrast to whole-cell MTB samples with magnetosome chain(s), THC-1 has distinctive magnetic properties. Together with previous studies, our results demonstrate that MTB magnetite has diverse magnetic properties that are distinctive but not necessarily unique compared to other magnetite types. This indicates that combining magnetic measurements and transmission electron microscope observations remains necessary for identifying magnetofossils.

The q-Rung orthopair fuzzy set (q-ROFS) is an effective and powerful tool for expressing fuzzy information. It can cover more complex and more hesitant fuzzy evaluation information. The aggregation operators are an effective tool to deal with decision problems, but when faced with these new types of fuzzy set whose operational rules are defective, they often causes a lot of information distortion. Therefore, based on the advantages of q-ROFSs, this paper presents a new extended fuzzy group TOPSIS method which doesn't need aggregation technology. This method can effectively reduce the distortion of decision information and improve the accuracy of evaluation results. In addition, this method involves an expert weight model, which can deal with the group decision problems with unknown weight of experts by using the importance of experts and the rationality of evaluation results. By using this weight model, the proposed method can effectively eliminate the unreasonable impact of the extreme evaluation value on the evaluation results, further solve the decision-making situation in which experts' opinions are divergent and experts are manipulated. In order to verify the effectiveness and superiority of the proposed method, this paper applies it to some practical examples and makes a detailed comparison with other existing methods. INDEX TERMS q-Rung orthopair fuzzy numbers, expert weight, TOPSIS method, multiple attribute group decision-making.