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Bacterial contractile injection systems (CIS) are phage tail-like macromolecular complexes that mediate cell-cell interactions by injecting effector proteins into target cells. CIS from (CIS ) are localized in the cytoplasm. Under stress, they induce cell death and impact the life cycle. It remains unknown, however, whether CIS require accessory proteins to directly interact with the cytoplasmic membrane to function. Here, we characterize the putative membrane adaptor CisA, a conserved factor in CIS gene clusters across species. We show by cryo-electron tomography imaging and in vivo assays that CIS contraction and function depend on CisA. Using single-particle cryo-electron microscopy, we provide an atomic model of the extended CIS apparatus; however, CisA is not part of the complex. Instead, our findings show that CisA is a membrane protein with a cytoplasmic N-terminus predicted to interact with CIS components, thereby providing a possible mechanism for mediating CIS recruitment to the membrane and subsequent firing. Our work shows that CIS function in multicellular bacteria is distinct from type VI secretion systems and extracellular CIS, and possibly evolved due to the role CIS play in regulated cell death.

Needle-free injection system (NFIS) is easy to operate and can decrease needle phobia. Besides, NFIS can increase the interaction of antigens in a more dispersed manner with immune cell at local injection site, which may improve the immune responses of mRNA vaccines. Although SARS-CoV-2 mRNA vaccines have great success, universal vaccines are urgently needed. Delivering universal mRNA vaccines by NFIS is preferred to combat COVID-19. RBD3-Fc mRNA expressing BA.4, Delta, and prototype RBD, and human IgG Fc with YTE mutation was designed and synthesized. The safety and immune responses of universal RBD3-Fc naked mRNA and mRNA-LNP vaccines delivered intradermally using NFIS (named GV-01) and intramuscularly via needles were evaluated and compared in rats. The prime-boost regimen administered by two routes resulted in potent immune responses and intradermal delivery displays comparable or better performance in terms of binding antibodies, neutralizing antibodies and T cell responses. Naked mRNA vaccines were functional, but less effective than mRNA-LNP vaccines. The above results suggest that RBD3-Fc vaccines are safe and immunogenic and NFIS can be used as an alternative to needles/syringes for the inoculation of mRNA-LNP vaccines to elicit robust systematic immune responses.

Antibiotic resistance poses a growing risk to public health, requiring new tools to combat pathogenic bacteria. Contractile injection systems, including bacteriophage tails, pyocins, and bacterial type VI secretion systems, can efficiently penetrate cell envelopes and become potential antibacterial agents. Bacteriophage XM1 is a dsDNA virus belonging to the Myoviridae family and infecting Vibrio bacteria. The XM1 virion, made of 18 different proteins, consists of an icosahedral head and a contractile tail, terminated with a baseplate. Here, we report cryo-EM reconstructions of all components of the XM1 virion and describe the atomic structures of 14 XM1 proteins. The XM1 baseplate is composed of a central hub surrounded by six wedge modules to which twelve spikes are attached. The XM1 tail contains a fewer number of smaller proteins compared to other reported phage baseplates, depicting the minimum requirements for building an effective cell-envelope-penetrating machine. We describe the tail sheath structure in the pre-infection and post-infection states and its conformational changes during infection. In addition, we report, for the first time, the in situ structure of the phage neck region to near-atomic resolution. Based on these structures, we propose mechanisms of virus assembly and infection.

This research describes a mechanism wherein a bacterium prompts the metamorphic development of an animal from larva to juvenile form by injecting a protein that disrupts membranes in the larval cilia. Specifically, results show that a bacterial contractile injection system and the protein effector it injects form pores in larval cilia, influencing critical signaling pathways like mitogen-activated protein kinase and calcium flux, ultimately driving animal metamorphosis. This discovery sheds light on how a bacterial protein effector exerts its activity through membrane disruption, a phenomenon observed in various bacterial toxins affecting cellular functions, and elicits a developmental response. This work reveals a potential strategy used by marine organisms to respond to microbial cues, which could inform efforts in coral reef restoration and biofouling prevention. The study’s insights into metamorphosis-associated contractile structures’ delivery of protein effectors to specific anatomical locations highlight prospects for future biomedical and environmental applications.

The swimming larvae of many marine animals identify a location on the sea floor to undergo metamorphosis based on the presence of specific bacteria. Although this microbe–animal interaction is critical for the life cycles of diverse marine animals, what types of biochemical cues from bacteria that induce metamorphosis has been a mystery. Metamorphosis of larvae of the tubeworm Hydroides elegans is induced by arrays of phage tail-like contractile injection systems, which are released by the bacterium Pseudoalteromonas luteoviolacea. Here we identify the novel effector protein Mif1. By cryo-electron tomography imaging and functional assays, we observe Mif1 as cargo inside the tube lumen of the contractile injection system and show that the mif1 gene is required for inducing metamorphosis. Purified Mif1 is sufficient for triggering metamorphosis when electroporated into tubeworm larvae. Our results indicate that the delivery of protein effectors by contractile injection systems may orchestrate microbe–animal interactions in diverse contexts. Many marine animals, including corals and tubeworms, begin life as larvae swimming in open water before transforming into adults that anchor themselves to the seabed. These transformations, known as metamorphoses, are often triggered by certain types of bacteria that form friendly relationships (or “symbioses”) with the animals. One such symbiosis forms between a bacterium called Pseudoalteromonas luteoviolacea and a tubeworm known as Hydroides elegans. Previous studies have shown that P. luteoviolacea produces syringe-like structures known as Metamorphosis Associated Contractile structures (or MACs for short) that are responsible for stimulating metamorphosis in the tubeworm larvae. Some viruses that infect bacteria use similar structures to inject molecules into their host cells. However, it was not clear whether MACs were also able to inject molecules into cells. Here, Ericson, Eisenstein et al. used a technique called cryo-electron tomography combined with genetic and biochemical approaches to study how the MACs of P. luteoviolacea trigger metamorphosis in tubeworms. The experiments identified a protein in the bacteria named Mif1 that was required for the tubeworms to transform. The bacteria loaded Mif1 into the tube of the MAC structure and then injected it into the tubeworms. Further experiments showed that inserting Mif1 alone into tubeworms was sufficient to activate metamorphosis. Mif1 is the first protein from bacteria to be shown to activate metamorphosis, but it is likely that many more remain to be discovered. Since other marine animals also form symbioses with bacteria, understanding how Mif1 and other similar proteins work may inform efforts to restore coral reefs and other fragile ecosystems, and increase the production of oysters and other shellfish. Furthermore, MACs and related structures may have the potential to be developed into biotechnology tools that deliver drugs and other molecules directly into animal cells.

Leachate injection in bioreactor landfills increases the moisture content within the municipal solid waste and facilitates rapid waste decomposition, thereby leading to early waste stabilization. Three types of leachate injection systems (LIS), namely, horizontal trenches (HT), vertical wells (VW), and drainage blankets (DB), are commonly used for leachate injection in bioreactor landfills. This study compares the performance of the three LIS to distribute a specific amount of injected leachate into a typical bioreactor landfill configuration considering the effects of waste characteristics, the rate of leachate injection, the mode of leachate injection, and saturated and unsaturated hydraulic conductivity parameters. A numerical two-phase flow model is used to predict evolution of saturation levels, pore-fluid pressures, when subjected to the same volume of leachate injection. Based on the results, the relative effectiveness of each LIS for achieving maximum uniform moisture distribution without inducing excessive pore-fluid pressures is determined. The results showed that the DB is effective in uniformly distributing the leachate and increasing the moisture levels across the landfill than the HT and VW for the same leachate injection rates. Intermittent mode of leachate injection was found to induce lower pore-water pressures in the waste while maintaining required saturation levels. The unsaturated hydraulic properties of waste were found to have considerable impact on moisture distribution by affecting the hydraulic conductivity of waste.

Petroleum is an indispensable energy source in modern industrial society, and maintaining the safe and stable operation of its injection and production system is of great significance. To analyze the mechanism of pipeline damage caused by corrosion and scaling in the injection production system, taking a water injection pipeline in an oil field as an example, the causes of corrosion and scaling damage were studied by detecting pipeline samples and analyzing corrosion products and various service conditions of the pipeline. The results showed that there was more scaling on the inner wall of the pipeline, and there was local corrosion in the pipeline sections that had experienced water injection, shutdown, and gas injection conditions, while there was no significant corrosion thinning in the pipeline sections that had only experienced water injection and shutdown conditions. The scale layer formed under water injection conditions is mainly composed of barium strontium sulfate (Ba0.75Sr0.25SO4), barium sulfate (BaSO4) and a small amount of silica (SiO2). The main reason for scale formation is the high content of barium ions (Ba2+) in the injected water. The corrosion products formed under gas injection conditions, including strontium ions (Sr2+) and sulfate ions (SO42−), are mainly composed of ferrous carbonate (FeCO3) and ferric oxide (Fe2O3). The pipeline corrosion product FeCO3 is mainly caused by carbon dioxide (CO2) in the medium. In addition, the high liquid content, cecal position, high Cl− (chloride ion) content, and slightly acidic environment in the pipeline also accelerate the occurrence of corrosion damage. The Fe2O3 in the corrosion products is formed when the pipeline is exposed to air after sampling, and is not the main cause of pipeline corrosion.

Endosymbiotic bacteria have evolved intricate delivery systems that enable these organisms to interface with host biology. One example, the extracellular contractile injection systems (eCISs), are syringe-like macromolecular complexes that inject protein payloads into eukaryotic cells by driving a spike through the cellular membrane. Recently, eCISs have been found to target mouse cells 1 – 3 , raising the possibility that these systems could be harnessed for therapeutic protein delivery. However, whether eCISs can function in human cells remains unknown, and the mechanism by which these systems recognize target cells is poorly understood. Here we show that target selection by the Photorhabdus virulence cassette (PVC)—an eCIS from the entomopathogenic bacterium Photorhabdus asymbiotica —is mediated by specific recognition of a target receptor by a distal binding element of the PVC tail fibre. Furthermore, using in silico structure-guided engineering of the tail fibre, we show that PVCs can be reprogrammed to target organisms not natively targeted by these systems—including human cells and mice—with efficiencies approaching 100%. Finally, we show that PVCs can load diverse protein payloads, including Cas9, base editors and toxins, and can functionally deliver them into human cells. Our results demonstrate that PVCs are programmable protein delivery devices with possible applications in gene therapy, cancer therapy and biocontrol. The tail fibre of an extracellular contractile injection system (eCIS) from Photorhabdus asymbiotica recognizes targets expressed on eukaryotic host cells, and can be reprogrammed to target specific organisms and cell types for delivery of novel protein payloads.

Contractile injection systems mediate bacterial cell-cell interactions by a bacteriophage tail–like structure. In contrast to extracellular systems, the type 6 secretion system (T6SS) is defined by intracellular localization and attachment to the cytoplasmic membrane. Here we used cryo-focused ion beam milling, electron cryotomography, and functional assays to study a T6SS in Amoebophilus asiaticus. The in situ architecture revealed three modules, including a contractile sheath-tube, a baseplate, and an anchor. All modules showed conformational changes upon firing. Lateral baseplate interactions coordinated T6SSs in hexagonal arrays. The system mediated interactions with host membranes and may participate in phagosome escape. Evolutionary sequence analyses predicted that T6SSs are more widespread than previously thought. Our insights form the basis for understanding T6SS key concepts and exploring T6SS diversity.

The article discusses the possibilities of detecting defects in the marine diesel engine injection system on a selected example. Basing on statistical data, it was pointed out that these engines had a significant failure rate in relation to the failure rate of other machinery and equipment used on ships. First, it concerns damage of the elements of the injection systems. Therefore, basing on the results of the authors’ own research, the possibility of improving diagnostic methods of the injection system that can be used in the ship operation process was pointed out. First, high diagnostic effectiveness of the analysis of pressure changes measured in the injection system was pointed out here. At the same time, taking into account the difficulties of such measurement in the conditions of the ship’s power plant, it has been shown that very good diagnostic effects can be obtained by using indicator diagrams to calculate heat release characteristics. On the selected damage of the injection pump example, the diagnostic usefulness of net heat release (Q) and intensity of heat release (q) has been shown. The improvement of diagnostic methods allows increasing the efficiency of diagnosis of marine engines.