An Engineered Escherichia coli Community for Studying Quorum Sensing

In bacterial communities, quorum sensing (QS) is a process mediated via chemical signalling that individuals use to coordinate their collective phenotypes. It is closely associated with pathogenic traits such as virulence factor production and antibiotic resistance. In their natural habitats, bacteria live in small niches, forming intricate consortia, where the role of QS is little understood. This work aims to construct a tuneable, trackable, and reconfigurable model bacterial community for studying QS. To this end, three Escherichia coli fluorescent reporter strains were constructed based on the paradigm LuxI/LuxR QS system. The strains recreate the three major aspects of QS response: sensing (S), autoinducer production (P), and regulation (R). We found that the response of the S strain as a function of the N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) concentration did not saturate and exhibited a concentration-dependent response (in the range 10−7 to 10−4 M). The P strain produced OHHL and showed the ability to activate the S response, while the R strain showed the ability to attenuate the response due to the expression of the lactonase AiiA. Monitoring the fluorescent signals of the strains permits tracking the activation and attenuation activities of the LuxI/LuxR QS system. Future studies can now also benefit from this straightforward subcloning strategy to study other QS systems

Characterisation of locust bean gum with asymmetric flow field-flow fractionation (AF4) and light scattering

We present a detailed characterisation of locust bean gum (LBG), an industrially significant galactomannan, utilising asymmetric flow field-flow fractionation (AF4) and light scattering. Molecular weight and size determination of galactomannans is complicated by their tendency to aggregate, even in dilute solutions; AF4 allows us to confirm the presence of aggregates, separate these from well-dispersed polymer, and characterise both fractions. For the dispersed polymer, we find Mw=9.2×105 g mol−1 and Rg,z=82.1 nm; the distribution follows Flory scaling (Rg∼Mν) with ν∼ 0.63, indicating good solvent conditions. The aggregate fraction exhibited radii of up to 1000 nm and masses of up to 3×1010 g mol−1. Furthermore, we demonstrate how both fractions are influenced by changes to filtration procedure and solvent conditions. Notably, a 200 nm nylon membrane effectively removes the aggregated fraction; we present a concentration-dependent investigation of solutions following this protocol, using static and dynamic light scattering, which reveals additional weak aggregation in these unfractionated samples. Overall, we demonstrate that AF4 is highly suited to LBG characterisation, providing structural information for both well-dispersed and aggregated fractions, and expect the methods employed to apply similarly to other galactomannans and associating polymer systems

Composition, characterisation and emulsifying properties of natural nanoparticles in chickpea aquafaba for the formation of chilli oleoresin-in-water Pickering emulsions

This study aims to assess the compositional characteristics of British Kabuli chickpea aquafaba (AF) by conducting a comprehensive analysis from raw chickpeas to centrifugation fractions of AF and its potential use in forming and stabilising capsaicin-loaded O/W Pickering systems by exploiting the presence of self-assembled nanoparticles and proteins, which act as natural-coating agent. To this end, chickpeas were soaked (16 h, 4 °C, 1:4 chickpea: water) and pressure-cooked (20 min, 113 °C, 10 psig, 1:5 chickpea: water). The dry weight-based (DWB) compositions included total carbohydrate (76.33 ± 4.20%), protein (16.29 ± 0.43%), total phenolics (7.05–8.77 mg/g) and saponins (39.95 ± 0.89 mg/g), thus confirming the leaching of these components from seeds to AF. SDS-PAGE electrophoresis analysis revealed the presence of low MW proteins (≤∼16 kDa). The monosaccharides comprised d-glucose, d-galactose, l-arabinose, d-xylose and d-fructose. AF's particle size distribution revealed the occurrence of a bimodal population of nanoparticles (Dh ≤∼1000 nm and Dh ≤∼100 nm), further characterised by SAXS and TEM imaging. O/W emulsions were prepared with three chilli oleoresin types (capsicum, chilli birds' eye, and chilli ancho) by high-pressure homogenisation. The emulsion with the highest capsaicin content (capsicum oleoresin) was the most stable while the emulsion with the lowest capsaicin content (chilli ancho oleoresin) was the least stable. The presence of incidental nanoparticles and denatured proteins in AF was reasoned to account for the formation and stabilisation of chilli oleoresin-in-water Pickering emulsions, a newly offered explanation for its interfacial properties that will be pursued further in future studies

Effect of protein extraction and fractionation of chia seeds grown in different locations: Nutritional, antinutritional and protein quality assessment

Chia (Salvia hispanica) has become increasingly popular in recent years due to its high protein content, among other nutritional benefits. This study aims to evaluate the nutritional and antinutritional composition, protein profile and protein quality of two chia seeds grown in Mexico and the UK, as well as to assess the impact that occurs during protein extraction and fractionation. Protein content of chia samples showed an increase after degumming, defatting, and extraction, obtaining protein concentrates from Mexican (MPC) and British (BPC) chia seeds with 88.32 and 89.20 g/100 g dw, respectively. Main protein fractions found in both chia seeds were globulins (Glo) and albumins (Alb). Essential amino acid index (EAAI) of chia samples ranged between 189.40 and 496.73% showing a 2-fold increase in comparison to the reference protein. In vitro protein digestibility (IVPD) increased after protein extraction (91% for MPC and BPC) but decreased after fractionation (∼68%). Trypsin inhibitors increased 78–82% after protein extraction, while total phenolics content (TPC) increased 7.77- and 5.76-fold for Mexican albumins (MAlb) and British albumins (BAlb), respectively. Phytic acid content showed a reduction of > 90% after extraction/fractionation. These findings showed that depending on the extraction and/or fractionation methods used the protein quality, digestibility and antinutrients will be highly influenced

Effect of the ultrastructure of chitosan nanoparticles in colloidal stability, quorum quenching and antibacterial activities

We have fabricated two types of crosslinked chitosan-based nanoparticles (NPs), namely (1) ionically crosslinked with tripolyphosphate (TPP), designated as IC-NPs and (2) dually co-crosslinked (ionically and covalently with TPP and genipin, respectively) termed CC-NPs. The two types of NPs were physichochemically characterized by means of DLS-NIBS, synchrotron SAXS and M3-PALS (zeta potential). First, we found that covalent co-crosslinking of ionically pre-crosslinked nanoparticles yielded monodisperse CC-NPs in the size range of ∼200 nm, whereas the parental IC-NPs remained highly polydisperse. While both types of chitosan nanoparticles displayed a core-shell structure, as determined by synchrotron SAXS, only the structure of CC-NPs remained stable at long incubation times. This enhanced structural robustness of CC-NPs was likely responsible of their superior colloidal stability even in biological medium. Second, we explored the antimicrobial and quorum sensing inhibition activity of both types of nanoparticles. We found that CC-NPs had lower long-term toxicity than IC-NPs. In contrast, sub-lethal doses of IC-NPs consistently displayed higher levels of quorum quenching activity than CC-NPs. Thus, this work underscores the influence of the NP’s ultrastructure on their colloidal and biological properties. While the cellular and molecular mechanisms at play are yet to be fully elucidated, our results broaden the spectrum of use of chitosan-based nanobiomaterialsin the development of antibiotic-free approaches against Gram-negative pathogenic bacteria

The Rosetta Stone of interactions of mucosa and associated bacteria in the gastrointestinal tract

Purpose of review Gut microbiota–mucosa–epithelial cells co-exist in an intricate three-way relationship that underpins gut homeostasis, and ultimately influences health and disease conditions. The O-glycans of mucin glycoproteins have been uncovered as a centrepiece of this system, although understanding the phenomena at play at the molecular level has been challenging and subject to significant traction over the last years. The purpose of this review is to discuss the recent advances in the phenomena that mediate microbiota and mucus multidirectional interactions in the human gut. Recent findings The mucus biosynthesis and degradation by both commensal and pathogenic bacteria is under tight regulation and involves hundreds of carbohydrate-active enzymes (CAZy) and transporters. The fucosylation of O-glycans from mucin-2 seems to dictate binding by pathogenic species and to influence their virulence. Less clear is the influence of O-glycans in quorum sensing and biofilm formation. We have reviewed the advances in the in vitro models available to recreate the phenomena that capture the physiological context of the intestinal environment, emphasising models that include mucus and other aspects relevant to the physiological context. Summary The recent findings highlight the importance of merging advances in analytical (glycans analysis) and omics techniques along with original robust in vitro models that enable to deconstruct part of the high complexity of the living gut and expand our understanding of the microbes-mucosa relationships and their significance in health and disease

Emulsifying properties of mesquite gum

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A rapid and portable fluorescence spectroscopy staining method for the detection of plastic microfibers in water

We propose a simple technique for microplastic detection based on their interaction with a hydrophilic and anionic fluorescent dye 1,3,6,8 pyrene tetrasulfonate (PTSA). Synthetic microfibers derived from surgical face masks (an abundantly generated plastic waste post COVID) were considered as model microplastics. The interactions between microfibers and the dye were studied as a function of physiological parameters (pH, contact time and temperature), external agents, dye dosage and polymer variants. A pocket-sized photometer (by Lovibond Tintometer group) was employed for the detection and further validated using advanced equipment set-ups (fluorescence microscope, Fourier transform infrared spectroscopy and benchtop spectrofluorometer). Risk assessment studies were conducted on Artemia salina as a model organism. As a risk mitigation strategy, dye recovery followed by sunlight mediated degradation were performed. The detection study was performed in real water samples collected from fresh, estuarine and seawater samples spiked with microfibers. As an outcome, an optimized standard operational conditions were determined for the effective detection of synthetic microfibers. The data obtained could have scientific and industrial impact, in particular for experts working in the broad arena of clean water, who are specifically interested in developing cost-effective solutions for effective detection and biomonitoring of emerging pollutants

On the gelling behaviour of 'nopal' (<i>Opuntia ficus indica</i>) low methoxyl pectin

International audienc