Archaic chaperone-usher pilus self-secretes into a superelastic zigzag spring architecture

Adhesive pili are hair-like appendages assembled via the chaperone-usher pathway (CUP) that mediate host tissue colonization and biofilm formation of Gram-negative bacteria 1-3. Archaic CUP pili, the most diverse and widespread CUP adhesins, are promising vaccine and drug targets due to their prevalence in the most troublesome multidrug-resistant (MDR) pathogens 1,4,5. However, their architecture and assembly-secretion process remain unknown. Here, we present the 3.4 Å resolution cryo-electron microscopy structure of the prototypical archaic Csu pilus that mediates biofilm formation of Acinetobacter baumannii, a notorious MDR nosocomial pathogen. In contrast to the thick helical tubes of the classical CUP pili, archaic pili assemble into a conceptually novel ultrathin zigzag architecture secured by an elegant clinch mechanism. The molecular clinch provides the pilus with high mechanical stability as well as superelasticity, a property observed now for the first time in biomolecules, while enabling a more economical and faster pilus production. Furthermore, we demonstrate that clinch formation at the cell surface drives pilus secretion through the outer membrane. These findings suggest that clinch-formation inhibitors might represent a new strategy to fight MDR bacterial infections.

Modeling time-temperature history and sterilization value of mango puree under conventional and microwave assisted pasteurization

Continuous pasteurization of liquid foods has to provide the desired lethality level to guarantee food safety with minimum degradation of quality attributes (sensorial and nutritional characteristics) and high energy efficiency. To optimize quality and cost, a thermal process should be modeled considering flow, heat transfer and mass dispersion principles; however, flow through helical tubes and microwave heating require a complex 3D multiphysics approach. Herein a simplified 2D approach is presented to model a hybrid pasteurization unit with conventional and microwave heating under laminar flow to predict axial and radial distributions of temperature and residual activity of a microorganism or enzyme. A study case of 20 °Brix mango puree (power law fluid) processing is used to test the model based on an existing pilot plant unit. Results were useful to compare conventional and microwave heating regarding the process sterilization value and model can be used for process analysis, design and optimization.

Analysis of heat transfer oscillation and buoyancy effects of supercritical R1234ze(E) cooled in horizontal helically coiled tubes

The helically coiled tubes have been attracting huge attention for enhancing the heat transfer of supercritical fluids and improving energy efficiency. Moreover, the new refrigerant R1234ze(E) has excellent environmental properties and system performance, but few studies have been focused on the supercritical R1234ze(E) heat transfer. In this work, the SST turbulence model is adopted for the numerical simulation of the cooling heat transfer performance of s-R1234ze(E) in horizontal helically coiled tubes. The influences of heat flux, mass flux, coil pitch, and tube radius on the heat transfer coefficient, gravitational buoyancy effect, and centrifugal buoyancy effect are respectively investigated. Furthermore, the results reveal heat transfer oscillation occurs when, and the oscillation mechanism is analyzed. Different from that in the vertical helical tube, the angle between the radial component of gravitational buoyancy and centrifugal force changes continuously in the horizontal helical tube, resulting in the fluid with lower temperature may locate in the inner-left region or the inner-right region. Subsequently, the heat transfer piecewise correlation applicable for supercritical R1234ze(E) in horizontal helical tubes is developed. The average absolute deviation of the predicted results is 5.88%.