Unraveling the Genetic Adaptations in Cell Surface Composition and Transporters of Lactiplantibacillus plantarum for Enhanced Acid Tolerance

This study employed adaptive laboratory evolution to improve the acid tolerance of Lactiplantibacillus plantarum, a vital strain in food fermentation and a potential probiotic. Phenotype and genomic analyses identified the overexpression of stress response proteins, ATP synthases, and transporters as pivotal in conferring acid tolerance to the evolved strains. These adaptations led to a shorter lag phase, improved survival rates, and higher intracellular pH values compared to the wild-type strain under acid stress conditions. Additionally, the evolved strains showed an increased expression of genes in the fatty acid synthesis pathway, resulting in a higher production of unsaturated fatty acids. The changes in cell membrane composition possibly prevented H+ influx, while mutant genes related to cell surface structure contributed to observed elongated cells and thicker cell surface. These alterations in cell wall and membrane composition, along with improved transporter efficiency, were key factors contributing to the enhanced acid tolerance in the evolved strains.

Safety Considerations for Lyophilized Human Amniotic Membrane Impregnated with Colistin and Silver Nanoparticles

Lyophilized human amniotic membrane (HAM) and silver nanoparticles (AgNPs) have multispectral applications as a biological dressing. The present study focuses on the safety aspects of HAM coated with colistin and AgNPs (HACoN) dressing in relation to its structural and hematological changes. Four dressing groups were designed for the study, HAM, HAM coated with colistin (HACo), HAM coated with AgNPs (HAN), and HAM coated with colistin (HACo) and HACoN. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were utilized for constitutional analysis. Biological safety was checked by applying HAM of all groups on open excisional burn wounds on Sprague-Dawley rats for 21 days. The skin, kidneys, liver, and spleen were removed, and histological analysis was performed for detailed structural analysis. Oxidative stress was assessed using homogenate from newly generated skin. No structural or biochemical change was observed in any of the study groups as observed by SEM and FTIR. After 21 days of grafting, wounds were healed properly with normal skin, and no anomaly was observed in related to kidneys, spleen, and liver. Some of antioxidant enzymes were increased, while malondialdehyde which is a reactive oxygen species was reduced in the skin tissue homogenate of HACoN group. Impregnation of colistin and AgNPs in combination on HAM has no effects on hematological and structural constitution of HAM. It leaves no obvious change in vital organs of rats and improves oxidative stress and inflammation. Hence, it can be claimed that HACoN is a biologically safe antibacterial dressing.

Comprehensive Analysis of the Physiological Characterization of Escherichia coli Nissle 1917

Escherichia coli Nissle 1917 (EcN) is one of the probiotics that has drawn more attention from researchers in recent days as it extends many host beneficial effects. EcN is being used as a treatment regimen especially for gastrointestinal disorders for more than 100 years. Apart from its clinical applications in its original form, EcN is being genetically engineered to meet the therapeutic requirements which ultimately led to the gradual transformation of EcN from being a mere food supplement to a complex therapeutic agent. However, comprehensive analysis of physiological characterization of EcN is inadequate. In this study, we have systematically studied various physiological parameters and found that EcN grows very well at the normal as well as at stressful conditions such as temperature (30, 37 and 42 °C), nutritional (minimal and LB), pH (ranging from 3 to 7) and osmotic stress (0.4 M NaCl, 0.4 M KCl, 0.4 M Sucrose and salt conditions). However, EcN shows nearly onefold reduction in viability at extreme acidic conditions (pH 3 and 4). It produces biofilm and curlin very efficiently compared to the laboratory strain MG1655. Through genetic analysis we have also shown that EcN exhibits high level of transformation efficiency and greater ability to retain heterogenous plasmid. Very interestingly, we have found that EcN is highly resistant to P1 phage infection. Since, EcN is being exploited largely for its clinical and therapeutic applications, the results that we have reported here would add more value and further expand its scope in clinical and biotechnological research.

Bacteria hinder large-scale transport and enhance small-scale mixing in time-periodic flows

Understanding mixing and transport of passive scalars in active fluids is important to many natural (e.g., algal blooms) and industrial (e.g., biofuel, vaccine production) processes. Here, we study the mixing of a passive scalar (dye) in dilute suspensions of swimming Escherichia coli in experiments using a two-dimensional (2D) time-periodic flow and in a simple simulation. Results show that the presence of bacteria hinders large-scale transport and reduces overall mixing rate. Stretching fields, calculated from experimentally measured velocity fields, show that bacterial activity attenuates fluid stretching and lowers flow chaoticity. Simulations suggest that this attenuation may be attributed to a transient accumulation of bacteria along regions of high stretching. Spatial power spectra and correlation functions of dye-concentration fields show that the transport of scalar variance across scales is also hindered by bacterial activity, resulting in an increase in average size and lifetime of structures. On the other hand, at small scales, activity seems to enhance local mixing. One piece of evidence is that the probability distribution of the spatial concentration gradients is nearly symmetric with a vanishing skewness. Overall, our results show that the coupling between activity and flow can lead to nontrivial effects on mixing and transport.

Humidity-Dependent Decay of Viruses, but Not Bacteria, in Aerosols and Droplets Follows Disinfection Kinetics

The transmission of some infectious diseases requires that pathogens can survive (i.e., remain infectious) in the environment, outside the host. Relative humidity (RH) is known to affect the survival of some microorganisms in the environment; however, the mechanism underlying the relationship has not been explained, particularly for viruses. We investigated the effects of RH on the viability of bacteria and viruses in both suspended aerosols and stationary droplets using traditional culture-based approaches. Results showed that viability of bacteria generally decreased with decreasing RH. Viruses survived well at RHs lower than 33% and at 100%, whereas their viability was reduced at intermediate RHs. We then explored the evaporation rate of droplets consisting of culture media and the resulting changes in solute concentrations over time; as water evaporates from the droplets, solutes such as sodium chloride in the media become more concentrated. Based on the results, we suggest that inactivation of bacteria is influenced by osmotic pressure resulting from elevated concentrations of salts as droplets evaporate. We propose that the inactivation of viruses is governed by the cumulative dose of solutes or the product of concentration and time, as in disinfection kinetics. These findings emphasize that evaporation kinetics play a role in modulating the survival of microorganisms in droplets.