Development, structure and mechanics of a synthetic E. coli outer membrane model

Advancements in Escherichia coli secretion systems for enhanced recombinant protein production

Escherichia coli is inarguably one of the most studied microorganisms across the spectrum of microbiology. It is very widely used in recombinant protein production owing to its rapid growth, ease of genetic manipulation, and relatively high protein yields. Despite all of its advantages, its inability to efficiently secrete proteins naturally remains a drawback leading to protein aggregation as inclusion bodies in the cytoplasm and consequent low overall protein yield. Therefore, many approaches to mitigate this weakness and enhance extracellular secretion to increase protein yield have been devised. This review explores the natural and engineered secretion systems in E. coli, highlighting their potential for enhanced protein secretion for non-glycosylated proteins. Natural one-step (e.g., Type I and III Secretion Systems) and two-step systems (e.g., Sec and Tat pathways) are detailed alongside recent advancements in genetic engineering, mutagenesis, and synthetic biology approaches aimed at improving protein yield, folding, and secretion efficiency. Emerging technologies, such as the ESETEC® and BacSec® platforms, promise scalable and cost-effective solutions for higher protein production. Challenges, including limited cellular capabilities and protein aggregation, are addressed through innovative strategies like cell wall modification, co-expression of chaperones, and medium optimization. This review emphasizes E. coli's adaptability to industrial applications, and the promising future of recombinant protein technologies.

The Effect of Lipopolysaccharides from Salmonella enterica on the Size, Density, and Compressibility of Phospholipid Vesicles

The properties of the large unilamellar vesicles (LUVs) from 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC), modified by lipopolysaccharides (LPS) from Salmonella enterica sv. Enteritidis, which mimics Gram-negative bacteria, were studied by various physical methods. LPS, in the range of 0/20/50 % w/w relative to the lipid, had a regulatory role in the structure of the LUVs toward the lower size, low polydispersity, and over-a-month size stability due to the lower negative zeta potential. The addition of LPS resulted in increased density, which determined the ultrasound velocity and the specific adiabatic compressibility. In a 0.5/1/2 mg/mL concentration range, the total lipid content did not significantly affect the size of LUVs and influenced the density-related attributes similarly to the LPS content. A positive correlation was found between temperature and vesicle size, and a negative correlation was found between temperature and density and compressibility-except for the anomaly behavior at 25 °C, around the melting point of DMPC.

Nanostructural and nanomechanical alterations of photosensitized lipid membranes due to light induced formation of reactive oxygen species

Photosensitization has a wide range of applications in vastly distant fields. Three key components must be present at the same time to trigger the related photodynamic effect: light, the photosensitizer (PS) and oxygen. Irradiating the sensitizer leads to the formation of reactive oxygen species (ROS). Since PSs are accumulated preferably in lipid membranes, the study of photoinduced damage to membrane lipids can greatly increase our understanding of the effect of ROS on membranes in pathological as well as therapeutic conditions. We aimed to characterize the topographical and nanomechanical changes in supported lipid bilayers (SLBs) evoked by light-induced ROS formation. SLBs were prepared on mica surfaces by deposition of liposomes containing unsaturated lipid components. Topographical changes of SLBs were imaged by atomic force microscopy (AFM), and ROS-induced nanomechanical alterations of the membranes were assessed by AFM force measurements. To shed light on chemical alterations of the membrane constituents, infrared spectra were recorded. In the AFM images of porphyrin-containing membranes nanoscopic, bilayer-spanning holes were detected after irradiation. The measured rupture forces increased as a result of irradiation. These phenomena did not occur in membranes lacking unsaturated lipid components, emphasizing their role in ROS-mediated disruption confirmed by infrared spectroscopy results.

Antibacterial, bacteriolytic, antibiofilm, and synergistic effects of the peel oils of Citrus microcarpa and Citrus x amblycarpa with tetracycline against foodborne Escherichia coli

Citrus essential oils (EOs) have shown significant antibacterial activity. The present study was undertaken to evaluate the antibacterial activity of the peel oils of Citrus microcarpa and C. x amblycarpa against Escherichia coli. The minimum inhibition concentration (MIC) was determined by using the broth microdilution assay. The checkerboard method was used to identify synergistic effects of the EOs with tetracycline, while bacteriolysis was assessed by calculating the optical density of the bacterial supernatant, crystal violet assay was used to assess their antibiofilm. Ethidium bromide accumulation test was employed to assess efflux pump inhibition. Electron microscope analysis was performed to observe its morphological changes. The EOs of C. microcarpa and C. x amblycarpa were found to contain D-limonene major compound at 55.78% and 46.7%, respectively. Citrus microcarpa EOs exhibited moderate antibacterial against E. coli with a MIC value of 200 μg/mL. The combination of C. microcarpa oil (7.8 μg/mL) and tetracycline (62.5 μg/mL) exhibited a synergy with FICI of 0.5. This combination inhibited biofilm formation and disrupt bacterial cell membranes. Citrus microcarpa EOs blocked the efflux pumps in E. coli. Citrus microcarpa EOs demonstrated promising antibacterial activity, which can be further explored for the development of drugs to combat E. coli.

Near-infrared responsive sulfur vacancy-rich CuS nanosheets for efficient antibacterial activity via synergistic photothermal and photodynamic pathways

Defect engineering has been proven to be an effective approach for electronic structure modulation and plays an important role in the photocatalytic performance of nanomaterials. In this study, a series of CuS nanosheet sulfur vacancies (V_S) are constructed by a simple hydrothermal synthesis method. The CuS with the highest V_S concentration exhibits strong antibacterial performance, achieving bactericidal rates of 99.9% against the Gram-positive Bacillus subtilis and Gram-negative Escherichia coli bacteria under 808 nm laser irradiation. Under illumination, the temperature of the catalyst increases from 23.5 °C to 53.3 °C, and with a high photothermal conversion efficiency of 41.8%. For E. coli and B. subtilis, the reactive oxygen species (ROS) production that is induced by the CuS group is 8.6 and 9.6 times greater, respectively, than that of the control group. The presence of V_S facilitates the enhancement of the light absorption capacity and the separation efficiency of electron-hole pairs, thereby resulting in improved photocatalytic performance. The synergistic effect of photothermal therapy (PTT) and photodynamic therapy (PDT) is aimed at causing oxidative damage and leading to bacterial death. Our findings provide an effective antibacterial strategy and offer new horizons for the application of CuS catalysts with V_S in the NIR region.

Model architectures for bacterial membranes

The complex composition of bacterial membranes has a significant impact on the understanding of pathogen function and their development towards antibiotic resistance. In addition to the inherent complexity and biosafety risks of studying biological pathogen membranes, the continual rise of antibiotic resistance and its significant economical and clinical consequences has motivated the development of numerous in vitro model membrane systems with tuneable compositions, geometries, and sizes. Approaches discussed in this review include liposomes, solid-supported bilayers, and computational simulations which have been used to explore various processes including drug-membrane interactions, lipid-protein interactions, host-pathogen interactions, and structure-induced bacterial pathogenesis. The advantages, limitations, and applicable analytical tools of all architectures are summarised with a perspective for future research efforts in architectural improvement and elucidation of resistance development strategies and membrane-targeting antibiotic mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-021-00913-7.