The evaluation of Starmerella magnoliae X3 as a biodiesel feedstock based on triacylglycerol (TAG) production, lipid productivity, and fatty acid profile under nitrogen limitation and acidic pH conditions.

The effects of four initial culture pH values (3, 4, 5, and 6) and nitrogen limitation on growth, TAG accumulation, lipid production, fatty acid profile, and estimated biodiesel quality of Starmerella magnoliae X3 were investigated. TAG and lipid levels were measured by Nile Red fluorescence and sulfo-phospho-vanilin (SPV) techniques, respectively. The results showed that a combination of nitrogen limitation and acidic pH significantly (p < 0.05) increased TAG accumulation, total lipid contents, and lipid productivity in Starmerella magnoliae X3 compared to the control group. Under nitrogen limitation, the highest TAG accumulation was achieved at initial pHs of 3 and 5 after 72 h of cultivation, and the highest lipid productivity (0.306 g L-1 d-1) was observed after 48 h at pH 3; the major fatty acids at the four pH values were oleic acid (63.6%-64%), palmitoleic acid (11.3%-12.5%), stearic acid (9.7%-11.4%), and palmitic acid (9.4%-10%). In addition, both stresses were associated with lower iodine value and higher cetane number of the biodiesel compared to the control. These findings suggest that cultivation in a low-nitrogen medium at an initial pH of 3 or 5 holds promise in increasing TAG production in Starmerella magnoliae X3.

Peptide retention time prediction for hydrophilic interaction liquid chromatography at acidic pH in formic-acid based eluents.

Peptide separation selectivity was evaluated for hydrophilic interaction liquid chromatography (HILIC) ZIC-HILIC, ZIC-cHILIC, and XBridge Amide sorbents using formic acid as eluent additive (pH 2.7). Sequence-specific retention prediction algorithms were trained using retention datasets of ∼30,000 peptides for each column. Our retention models were able to attain ∼0.98 R2-value and yielded retention coefficients that can be probed to understand peptide-stationary phase interaction. Overall, the hydrophilicity for these columns decreased when the mobile phase changed pH from 4.5 to 2.7, when using 0.1 % formic acid in the mobile phase. The acidic residues became protonated, and the resultant hydrophilic interaction is dampened at the lower pH, leaving only the basic residues as the primary hydrophilic interactors. Hence, peptides of increasing charge have higher retention. In this comparison between the three columns, ZIC-HILIC has the highest chromatographic resolution between groups of peptides of different charge. From the position-dependent retention coefficients for ZIC-HILIC at pH 2.7, we found that the amino acids at the terminal positions of the peptide modulate the basicity of the N-terminal amino group or the C-terminal Arg/Lys for tryptic peptides. With respect to the separation orthogonality between HILIC and acidic pH RPLC for two dimensional separations, the orthogonality values were lower at pH 2.7 than operating HILIC at pH 4.5 for the first dimension. We also demonstrate that ZIC-HILIC was able to distinguish citrullinated and deamidated peptides based on predicted retention values.

Isolation of a Moderately Acidophilic Nitrobacter from a Nitrifying Community Supplied with Urea.

Nitrite-oxidizing bacteria (NOB), which perform the second step of aerobic nitrification, play an important role in soil. In the present study, we report a novel isolate from agricultural soil affiliated with the genus Nitrobacter and its physiological characteristics. We sampled the surface soil of a vegetable field and obtained mixed culture A31 using the most probable number (MPN) method with inorganic medium containing 0.75| |mM urea (pH 5.5). The dilution-extinction procedure on culture A31 led to the isolation of a strain that was designated as Nitrobacter sp. A67. The nxrB1 gene sequence of Nitrobacter sp. A67 (302 bp) was classified into Cluster 5, and the highest sequence identity was 96.10% with Nitrobacter sp. BS5/19. The NO2- oxidation activity of Nitrobacter sp. A67 was investigated at various pH. The optimum pH for NO2- oxidation was 5.8-6.4. This result indicates that Nitrobacter sp. A67 is a moderately acidophilic nitrite-oxidizing bacterium.

The pH-Insensitive Antimicrobial and Antibiofilm Activities of the Frog Skin Derived Peptide Esc(1-21): Promising Features for Novel Anti-Infective Drugs.

The number of antibiotic-resistant microbial infections is dramatically increasing, while the discovery of new antibiotics is significantly declining. Furthermore, the activity of antibiotics is negatively influenced by the ability of bacteria to form sessile communities, called biofilms, and by the microenvironment of the infection, characterized by an acidic pH, especially in the lungs of patients suffering from cystic fibrosis (CF). Antimicrobial peptides represent interesting alternatives to conventional antibiotics, and with expanding properties. Here, we explored the effects of an acidic pH on the antimicrobial and antibiofilm activities of the AMP Esc(1-21) and we found that it slightly lost activity (from 2- to 4-fold) against the planktonic form of a panel of Gram-negative bacteria, with respect to a ≥ 32-fold of traditional antibiotics. Furthermore, it retained its activity against the sessile form of these bacteria grown in media with a neutral pH, and showed similar or higher effectiveness against the biofilm form of bacteria grown in acidic media, simulating a CF-like acidic microenvironment, compared to physiological conditions.

Impact of multilamellar formulations on stratum corneum lipid organization and epidermal lipid barrier enhancement (Part II).

INTRODUCTION: The integrity of the stratum corneum (SC) is crucial for the skin's barrier function, protecting against environmental stressors and minimizing transepidermal water loss. Advances in skincare formulations have introduced multilamellar systems designed to emulate the SC's lipid composition and organization. This study hypothesizes that the application of a multilamellar cream will significantly impact the SC's lipid content and lamellar structure, thereby enhancing the epidermal barrier. METHODS: A saturated phosphatidylcholine-based multilamellar cream was applied to a cohort of adult subjects with very dry skin. Electron microscopy was utilized to analyse the micro-morphology of the cream and its integration into the lipid-depleted SC. Lipid analysis was conducted to quantify changes in the intercellular lipid matrix. RESULTS: Transmission-electron microscopy (TEM) imaging demonstrated that the multilamellar cream possesses a structured arrangement comparable to the natural SC architecture. Short-term application revealed a time-dependent restoration of lipid bilayers, while a 14-day regimen showed a marked increase in lipid lamellae density and length within the SC. Lipid analysis indicated a significant increase in total lipid content, with notable enhancements in ceramide and free fatty acid levels, without altering cholesterol levels. Lipid ratio analysis further confirmed the rebalancing of the SC's lipid composition. DISCUSSION: The multilamellar cream selectively increased specific lipids critical for barrier function, suggesting an action mechanism that aligns with the skin's natural regulatory processes. This selective augmentation indicates the potential of the formulation to not only restore but also enhance the epidermal barrier, with the maintenance of physiological lipid ratios suggesting compatibility with intrinsic repair mechanisms. CONCLUSION: The study confirms that a multilamellar cream can significantly improve the SC's lipid composition and structural integrity, indicating enhanced barrier function. They are pivotal for skincare professionals, dermatologists, and product developers, enriching the understanding of multilamellar creams' benefits and applications in improving epidermal barrier function.

INTRODUCTION: l'intégrité de la couche cornée (SC, stratum corneum) est essentielle pour la fonction de barrière cutanée, protégeant contre les facteurs de stress environnementaux et réduisant au minimum la perte d'eau transépidermique. Les progrès en matière de formulations pour soins de la peau ont introduit des systèmes multilamellaires conçus pour simuler la composition et l'organisation lipidique du SC. Cette étude émet l'hypothèse que l'application d'une crème multilamellaire aura un impact significatif sur la teneur en lipides et la structure lamellaire du SC, améliorant ainsi la barrière épidermique. MÉTHODES: Une crème multilamellaire à base de phosphatidylcholine saturée a été appliquée à une cohorte de sujets adultes présentant une peau très sèche. La microscopie électronique a été utilisée pour analyser la micromorphologie de la crème et son intégration dans le SC délipidé. Une analyse lipidique a été réalisée pour quantifier les changements dans la matrice lipidique intercellulaire. RÉSULTATS: l'imagerie par TEM a démontré que la crème multilamellaire possède un agencement structuré comparable à l'architecture naturelle du SC. L'application à court terme a révélé une restauration dépendante du temps des bicouches lipidiques, tandis qu'un schéma posologique de 14 jours a montré une augmentation marquée de la densité et de la longueur des lamelles lipidiques au sein du SC. L'analyse lipidique a indiqué une augmentation significative de la teneur lipidique totale, avec des améliorations notables des taux de céramide et d'acides gras libres, sans altérer les taux de cholestérol. L'analyse du rapport lipidique a confirmé le rééquilibrage de la composition lipidique du SC. DISCUSSION: la crème multilamellaire a augmenté de manière sélective les lipides spécifiques essentiels à la fonction de barrière, suggérant un mécanisme d'action qui s'aligne sur les processus de régulation naturels de la peau. Cette augmentation sélective indique le potentiel de la formulation non seulement à restaurer, mais également à améliorer la barrière épidermique, avec le maintien des rapports lipidiques physiologiques suggérant une compatibilité avec les mécanismes de réparation intrinsèques. CONCLUSION: l'étude confirme qu'une crème multilamellaire peut améliorer de manière significative la composition lipidique et l'intégrité structurelle du SC, ce qui indique une meilleure fonction de barrière. Ils sont essentiels pour les professionnels de la peau, les dermatologues et les développeurs de produits, et enrichissent la compréhension des bénéfices et des applications des crèmes multilamellaires dans l'amélioration de la fonction de la barrière épidermique.

Removal of Cadmium (II) from Aqueous Solution Using Galdieria sulphuraria CCMEE 5587.1.

The release of cadmium into the environment is a significant global concern due to its toxicity, non-biodegradability, and persistence in nature. There is an urgent need for effective, eco-friendly, and cost-effective systems for removing Cd because of the many drawbacks of conventional physicochemical techniques. This study investigated the ability of the extremophile red microalgal strain Galdieria sulphuraria CCMEE 5587.1 to tolerate and remove Cd (II) ions at acidic pH in a controlled laboratory environment. Three distinct concentrations of Cd (1.5 mg L-1, 3 mg L-1, and 6 mg L-1) were introduced to the cyanidium medium, and G. sulphuraria cells were introduced in the medium and grown for ten days. Four distinct aspects were identified regarding Cd removal: time course Cd removal, total Cd removal, extracellular Cd removal, and intracellular Cd removal. The inhibitory effects of Cd on G. sulphuraria growth were observed using a daily growth profile. Initial incubation days showed an inhibition of G. sulphuraria growth. In addition, increasing the Cd concentration in the medium decreased the growth rate of G. sulphuraria. Rapid Cd removal occurred on the first day of the experiment, followed by a steady removal of Cd until the last day. The highest total removal efficiency occurred in a medium containing 3 mg L-1 of Cd ions, which was 30%. In contrast, the highest sorption capacity occurred in a medium containing 6 mg L-1 of Cd ions, which was 1.59 mg g-1 of dry biomass. In all media compositions, a major fraction (>80%) of Cd removal occurred via adsorption on the cell surface (extracellular). These results showed that G. sulphuraria cells can remove Cd ions from aqueous solution, which makes them a potential bioremediation option for heavy metal removal.

Clinical efficacy of a multilamellar cream on skin physiology and microbiome in an epidermal stress model: A controlled double-blinded study.

INTRODUCTION: Stratum corneum (SC) is essential for skin barrier function, mitigating water loss and shielding against potentially harmful substances and allergens. The SC's lipid matrix, arranged in a lamellar structure, is integral to its protective role. Our study explores the restoration effects of a multilamellar cream with an acidic pH compared to a basic placebo cream on skin physiology and its interaction with the skin microbiome after stress induction via tape stripping (TS). MATERIALS AND METHODS: In this double-blind study, 14 healthy participants aged 21-58 years were assessed pre- and post-tape stripping, followed by a 14 days application of a multilamellar test cream and a placebo cream with evaluations on days 7, 14 and 17 for sustained effects. Skin physiology was analysed in terms of epidermal barrier function, SC hydration and surface pH. The microbiome was analysed by 16S rRNA amplicon sequencing the 16S rRNA gene using Illumina MiSeq, with subsequent species identification. RESULTS: Our study showed significant improvements in skin barrier repair and SC hydration with verum, particularly after 14 days of application, while both creams initially enhanced stratum corneum hydration. No significant changes in surface-pH were detected. The skin microbiome analysis revealed that TS slightly decreased alpha diversity, a trend that verum significantly reversed, enhancing diversity beyond baseline levels after 14 days. Overall, while both creams contributed to a broader microbial phyla diversity over time, no significant changes in the abundance of specific genera or species were noted between treatments. DISCUSSION AND CONCLUSION: Our study delineates the efficacy of a pH-optimized multilamellar cream in enhancing epidermal barrier recovery and SC hydration post-sequential TS, in contrast to an unstructured basic placebo. Verum cream significantly improved skin barrier function and SC hydration at day 14, with sustained effects evident beyond the treatment period. Furthermore, the multilamellar formulation facilitated the restitution of cutaneous microbiome diversity, a key indicator of healthy skin ecology, underscoring the symbiotic relationship between barrier integrity and microbial composition. These findings underscore the importance of multilamellar emollient structures in dermatological therapeutics, with potential implications for the design of advanced skincare interventions that holistically support cutaneous resilience and homeostasis.

INTRODUCTION: La couche cornée (stratum corneum, SC) est essentielle pour la fonction de barrière cutanée, atténuant la perte d'eau et protégeant contre les substances et allergènes potentiellement nocifs. Disposée selon une structure lamellaire, la matrice lipidique de la SC est constitutive de son rôle protecteur. Notre étude explore les effets de restauration d'une crème multilamellaire à pH acide par rapport à une crème placebo de base sur la physiologie de la peau et son interaction avec le microbiome de la peau après induction de stress via un test tape stripping (TS). MATÉRIELS ET MÉTHODES: Dans cette étude en double aveugle, 14 participants en bonne santé âgés de 21 à 58 ans ont été évalués avant et après tape stipping, puis ont procédé à l'application pendant 14 jours d'une crème test multilamellaire et d'une crème placebo avec des évaluations aux jours 7, 14 et 17 pour les effets durables. La physiologie de la peau a été analysée en termes de fonction de la barrière épidermique, d'hydratation SC et de pH de surface. Le microbiome a été analysé par séquençage de l'amplicon de l'ARNr 16S sur le gène de l'ARNr 16S à l'aide d'Illumina MiSeq, avec identification ultérieure des espèces. RÉSULTATS: Notre étude a montré des améliorations significatives de la réparation de la barrière cutanée et de l'hydratation SC avec le traitement actif, en particulier après 14 jours d'application, tandis que les deux crèmes avaient initialement amélioré l'hydratation de la couche cornée. Aucun changement significatif du pH de surface n'a été détecté. L'analyse du microbiome cutané a révélé que le TS diminuait légèrement la diversité alpha, une tendance qui s'est significativement inversée avec le traitement actif : une amélioration de la diversité au­delà des taux initiaux était observée après 14 jours. Dans l'ensemble, bien que les deux crèmes aient contribué à une plus grande diversité des phyla microbiennes au fil du temps, aucune variation significative dans l'abondance de genres ou d'espèces spécifiques n'a été observée entre les traitements. DISCUSSION ET CONCLUSION: Notre étude délimite l'efficacité d'une crème multilamellaire à pH optimisé pour améliorer la réparation de la barrière épidermique et l'hydratation SC après un TS séquentiel, contrairement à un placebo basique non structuré. La crème contenant le traitement actif a significativement amélioré la fonction de barrière cutanée et l'hydratation SC au jour 14, avec des effets durables évidents au­delà de la période de traitement. En outre, la formulation multilamellaire a facilité la restitution de la diversité du microbiome cutané, un indicateur clé d'une écologie de peau en bonne santé, soulignant la relation symbiotique entre l'intégrité de la barrière et la composition microbienne. Ces résultats soulignent l'importance des structures émollientes multilamellaires dans les traitements dermatologiques, avec des implications potentielles pour la conception d'interventions cutanées avancées qui soutiennent de manière holistique la résilience cutanée et l'homéostasie.

A Microtiter Plate Assay at Acidic pH to Identify Potentiators that Enhance Pyrazinamide Activity Against Mycobacterium tuberculosis.

Pyrazinamide (PZA) is a key component of chemotherapy for the treatment of drug-susceptible tuberculosis (TB) and is likely to continue to be included in new drug combinations. Potentiation of PZA could be used to reduce the emergence of resistance, shorten treatment times, and lead to a reduction in the quantity of PZA consumed by patients, thereby reducing the toxic effects. Acidified medium is required for the activity of PZA against Mycobacterium tuberculosis. In vitro assessments of pyrazinamide activity are often avoided because of the lack of standardization, which has led to a lack of effective in vitro tools for assessing and/or enhancing PZA activity.We have developed and optimized a novel, robust, and reproducible, microtiter plate assay, that centers around acidity levels that are low enough for PZA activity. The assay can be applied to the evaluation of novel compounds for the identification of potentiators that enhance PZA activity. In this assay, potentiation of PZA is demonstrated to be statistically significant with the addition of rifampicin (RIF), which can, therefore, be used as a positive control. Conversely, norfloxacin demonstrates no potentiating activity with PZA and can be used as a negative control. The method, and the associated considerations, described here, can be adapted in the search for potentiators of other antimicrobials.

Design of an Acidic pH-Activated NIR Fluorescent Convertible Rhodamine-Hemicyanine Probe-Peptide Conjugate for Living Cancer Cell Active Targeted Selective Tracking of Lysosomes.

We have synthesized an acidic pH-activatable dual targeting ratiometric fluorescent probe-peptide conjugate using the SPPS protocol on Rink amide AM resin. Living carcinoma cell specific active targeting, successive cell penetration, and selective staining of lysosomes are accomplished. Real-time monitoring of lysosomes, 3D, and multicolor cancer cell imaging are also attained. The de novo design consists of the integration of multifunctionality into a single molecular scaffold, e. g., RGDS peptide residue to target cancer cell surface overexpressed receptor αVß3 integrin, live-cell penetrating organic unsymmetrical rhodamine-hemicyanine chromophore comprising a lysosome targeting morpholine group, and an acidic pH openable spiro-lactam ring for a visible-to-NIR switchable ratiometric response. Water-soluble fluorescent probe-peptide conjugate exhibits intramolecular spirolactamization at basic pH through Arg amide N. The visible spirolactam state predominantly exists at physiological and basic pH and can be switched to the highly conjugated NIR open amide state (λem=735 nm) through spiro-lactam ring opening triggered by acidic pH with a huge bathochromic shift (Δλabs=336 nm, ΔλFL=265 nm). Moreover, pH-sensitive ratiometric optical switching is achieved. This in situ acidic cancer cell lysosome activatable multifunctional fluorophore-peptide conjugate shows augmented molar absorptivity, enhanced quantum yield, and improved fluorescence lifetime at acidic lysosomal pH; negligible cytotoxicity; and dual targeted ratiometric imaging capability of living cancer cell selective lysosomes with a pKa value of 5.1.

The expression of trefoil factor family member 2 in increased at an acidic pH.

Trefoil factor family member 2 (Tff2) is significantly involved in intestinal tumor growth in ApcMin/+ mice, which can be used as a human colon cancer model. TFF2, which encodes TFF2 (spasmolytic protein 1) is highly expressed in human cancer tissues, including the pancreas, colon and bile ducts, as well as in normal gastric and duodenum tissues. By contrast, TFF2 exhibits low expression levels in other normal tissues, including the small and large intestine. Furthermore, TFF2 expression has not been detected in DLD-1 cells, a cell line derived from human colon cancer. What induces TFF2 expression in normal and tumor cells is still unknown. Highly malignant tumor tissues are characterized by higher temperatures and lower pH (6.2-6.9) than in normal tissues, where normal pH ranges from 7.2 to 7.4. This microenvironment exacerbates malignancy by promoting the acquisition of cell death resistance, drug resistance and immune escape. Therefore, the present study examined how TFF2 expression is affected in cultured cells that imitate the tumor tissue microenvironment. The incubation temperature was increased from 37 to 40°C, but no expression of TFF2 was induced. Subsequently, a culture solution with an acidic pH was prepared to simulate the Warburg effect in tumors. TFF2 expression was increased by 42.8- and 5.8-fold in cells cultured in acidic medium at pH 6.5 and 6.8 compared with at pH 7.4, respectively, as determined using the relative quantification method following quantitative polymerase chain reaction. The present study also analyzed fluctuations in the expression levels of genes other than TFF2, under acidic conditions. Acidic conditions upregulated the expression of genes related to cell membranes and glycoproteins, based on the Database for Annotation, Visualization, and Integrated Discovery. In conclusion, TFF2 was highly expressed under acidic conditions, implying that it may have an important function in protecting the plasma membrane from acidic environments in both normal and cancer cells. These findings warrant further investigation of TFF2 as a target of cancer therapy and diagnosis.

Synthesis, characterization, and efficacy evaluation of a PH-responsive Fe-MOF@GO composite drug delivery system for the treating colorectal cancer.

Luteolin is a potent anti-colorectal cancer chemical. However, its effectiveness is hindered by its poor solubility in water and fat, and it is easy to degrade by gastrointestinal enzymes. In this study, a nano-composite carrier, NH2-MIL-101(Fe)@GO (MG), based on aminated MIL-101(Fe) and graphene oxide (GO) was developed and evaluated. This carrier co-delivered luteolin and matrine, while marine was used to balance the pH for the nano-preparation. The loading capacities for luteolin and matrine were approximately 9.8% and 14.1%, respectively. Luteolin's release at pH = 5 was significantly higher than at pH = 7.4, indicating it had an acidic pH response release characteristic. Compared to MOF and GO alone, MG and NH2-MIL-101(Fe)@GO@Drugs (MGD) enhanced anti-cancer activity by inhibiting tumor cell migration, increasing ROS generation, and upregulating the expression of Caspase-3 and Caspase-9. In conclusion, this study contributes new ideas and methods to the treatment strategy of multi-component anti-colorectal cancer therapy. It also advances drug delivery systems and supports the development of more effective and targeted treatment approaches for colorectal cancer.

Insights into the effect mechanism of acidic pH condition on the in vitro starch digestion of black highland barley semi-dried noodles.

In this study, black highland barley semi-dried noodles (BHBSNs) were adjusted to acidic pH (5.0, 4.5, 4.0) with an acidity regulator (monosodium fumarate) for obtaining low glycemic index (GI) BHBSNs, and the changes in the in vitro starch digestion, free phenolic content, and α-amylase activity in BHBSNs were investigated. The estimated glycemic index (eGI) of BHBSNs decreased from 59.23 to 52.59, 53.89 and 53.61, respectively, as the pH was adjusted from 6.0 to 5.0, 4.5, 4.0. As the pH of BHBSNs decreased, the equilibrium hydrolysis (C∞) decreased, and kinetic coefficient (k) decreased and then increased. Compared to the control, the pH of the digestive fluid decreased during digestion with decreasing pH, and the α-amylase inhibition of BHBSNs with pH 5.0, 4.5, and 4.0 increased by 56.54 %, 75.18 %, and 107.98 %, respectively. In addition, as the pH of BHBSNs decreased, the free phenolic content and the content of released phenolics during digestion increased. Pearson correlations analysis showed that the increase in α-amylase inhibition and phenolic release during digestion induced by acidic pH was negatively correlated with the eGI and C∞ of BHBSNs. This study indicated that acidic pH condition could modulate starch digestion for preparing low GI BHBSNs.

Acidic pH or salt treatment can convert soluble antibody aggregates in culture harvest into monomers and improve Protein A chromatography step yield.

While purifying a regular monospecific antibody, we found that the Protein A step yield was much lower than expected. Further studies revealed that the antibody formed large-size aggregates that did not bind to the Protein A resin, hence leading to dropped recovery. In an attempt to solve this low yield issue, we found that mildly acidic pH or ammonium sulfate treatment can partially convert the aggregates into monomers. In addition, when acidic pH treated culture harvest was processed by Protein A chromatography, the yield was restored to the normal range, suggesting that the monomers recovered from aggregates regained Protein A binding capability. Thus, low pH treatment of culture harvest can be potentially used as a general approach for improving Protein A step yield in cases where non-binding antibody aggregates are formed through noncovalent interactions.

Emulsifying properties of O/W emulsion stabilized by soy protein isolate and γ-polyglutamic acid electrostatic complex.

In order to improve the emulsifying properties of soy protein around isoelectric point, soy protein isolate (SPI) and γ-polyglutamic acid (γ-PGA) complexes were prepared by electrostatic interaction. The formation of SPI-γ-PGA electrostatic complex and emulsifying properties were investigated by monitoring turbidity, zeta potential, intrinsic fluorophores, emulsion characterization, and microstructure observation. The results showed that the formation of SPI-γ-PGA electrostatic complex was identified through turbidimetric analysis and zeta-potential measurement. Intrinsic fluorescence spectrum indicated internal structure changes of electrostatic complexes. Furthermore, SPI-γ-PGA complex-stabilized emulsions showed better stability with small droplet sizes and slow growth as well as the uniform microstructure around the isoelectric point (pH 4.0-5.0) than SPI-formed emulsions. Under the different thermal treatments and ionic strengths, emulsions stabilized by SPI-γ-PGA-soluble complex resulted in improved emulsion stability to environmental stresses. This may be attributed to the increased steric repulsion and electrostatic repulsion by SPI-γ-PGA complexes at oil-water interfaces. The findings derived from this research would provide theoretical reference about SPI-γ-PGA electrostatic complex that can be applied in acid beverages and developed a novel plant-based sustainable stabilizer for emulsions. PRACTICAL APPLICATION: The electrostatic interaction between SPI and γ-PGA improved the emulsifying characteristics of soy protein around isoelectric point. The results derived from this research would expand applications of SPI-γ-PGA-soluble electrostatic complex that can be applied in acid beverages, as well as a novel plant-based sustainable stabilizer for emulsions.

Molecular and cellular evidence of a direct interaction between the TRAF2 C-terminal domain and ganglioside GM1.

TNF receptor-associated factor 2 (TRAF2) is involved in different cellular processes including signal transduction and transcription regulation. We here provide evidence of a direct interaction between the TRAF domain of TRAF2 and the monosialotetrahexosylganglioside (GM1). Previously, we showed that the TRAF domain occurs mainly in a trimeric form in solution, but it can also exist as a stable monomer when in the nanomolar concentration range. Here, we report that the quaternary structure of the TRAF domain is also affected by pH changes, since a weakly acidic pH (5.5) favors the dissociation of the trimeric TRAF domain into stable monomers, as previously observed at neutral pH (7.6) with the diluted protein. The TRAF domain-GM1 binding was similar at pH 5.5 and 7.6, suggesting that GM1 interacts with both the trimeric and monomeric forms of the protein. However, only the monomeric protein appeared to cause membrane deformation and inward vesiculation in GM1-containing giant unilamellar vesicles (GUVs). The formation of complexes between GM1 and TRAF2, or its TRAF domain, was also observed in cultured human leukemic HAP1 cells expressing either the truncated TRAF domain or the endogenous full length TRAF2. The GM1-protein complexes were observed after treatment with tunicamycin and were more concentrated in cells undergoing apoptosis, a condition which is known to cause cytoplasm acidification. These findings open the avenue for future studies aimed at deciphering the physiopathological relevance of the TRAF domain-GM1 interaction.

Acidic pH modulates Burkholderia cenocepacia antimicrobial susceptibility in the cystic fibrosis nutritional environment.

IMPORTANCE: Burkholderia cenocepacia causes severe infections in cystic fibrosis (CF) patients. CF patients are prone to reoccurring infections due to the accumulation of mucus in their lungs, where bacteria can adhere and grow. Some of the antibiotics that inhibit B. cenocepacia in the laboratory are not effective for CF patients. A major contributor to poor clinical outcomes is that antibiotic testing in laboratories occurs under conditions that are different from those of sputum. CF sputum may be acidic and have increased concentrations of iron and zinc. Here, we used a medium that mimics CF sputum and found that acidic pH decreased the activity of many of the antibiotics used against B. cenocepacia. In addition, we assessed susceptibility to more than 500 antibiotics and found four active compounds against B. cenocepacia. Our findings give a better understanding of the lack of a relationship between susceptibility testing and the clinical outcome when treating B. cenocepacia infections.

Iron (Fe) toxicity, uptake, translocation, and physio-morphological responses in Catharanthus roseus.

Iron (Fe) toxicity in plant species depends on the availability of Fe in the soil, uptake ability by the root system, and translocation rate to other parts of the plant. The aim of this study was to assess Fe uptake by root tissues of Catharanthus roseus, translocation rate to leaf tissues, and the impairment of plant physio-morphological characteristics. Fe uptake by the roots (~ 700 µg g-1 DW) of C. roseus was observed during the early exposure period (1 week), and translocation factor from root to shoot was fluctuated as an independent strategy. A high level of Fe content in the root tissues significantly inhibited root length and root dry weight. Under acidic pH condition, an enrichment of Fe in the shoots (~ 400 µg g-1 DW) led to increase in leaf temperature (> 2.5 °C compared to control) and crop stress index (> 0.6), resulting in stomatal closure, subsequently decreasing CO2 assimilation rate and H2O transpiration rate. An increment of CSI in Fe-stressed plants was negatively related to stomatal conductance, indicating stomatal closure with an increase in Fe in the leaf tissues. High Fe levels in the leaf tissues directly induced toxic symptoms including leaf bronzing, leaf spotting, leaf necrosis, leaf chlorosis, and leaf senescence in C. roseus plants. In summary, C. roseus was identified as a good candidate plant for Fe phytoextraction, depending on Fe bioaccumulation, therefore 50 mM Fe treatment was designated as an excess Fe to cause the growth inhibition, especially in the prolonged Fe incubation periods. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01379-5.

Rhodamine-Based Cyclic Hydroxamate as Fluorescent pH Probe for Imaging of Lysosomes.

Monitoring the microenvironment within specific cellular regions is crucial for a comprehensive understanding of life events. Fluorescent probes working in different ranges of pH regions have been developed for the local imaging of different pH environments. Especially, rhodamine-based fluorescent pH probes have been of great interest due to their ON/OFF fluorescence depending on the spirolactam ring's opening/closure. By introducing the N-alkyl-hydroxamic acid instead of the alkyl amines in the spirolactam of rhodamine, we were able to tune the pH range where the ring opening and closing of the spirolactam occurs. This six-membered cyclic hydroxamate spirolactam ring of rhodamine B proved to be highly fluorescent in acidic pH environments. In addition, we could monitor pH changes of lysosomes in live cells and zebrafish.

Clinically relevant mutations in the PhoR sensor kinase of host-adapted Mycobacterium abscessus isolates impact response to acidic pH and virulence.

IMPORTANCE: Difficult-to-treat pulmonary infections caused by nontuberculous mycobacteria of the Mycobacterium abscessus group have been steadily increasing in the USA and globally. Owing to the relatively recent recognition of M. abscessus as a human pathogen, basic and translational research to address critical gaps in diagnosis, treatment, and prevention of diseases caused by this microorganism has been lagging behind that of the better-known mycobacterial pathogen, Mycobacterium tuberculosis. To begin unraveling the molecular mechanisms of pathogenicity of M. abscessus, we here focus on the study of a two-component regulator known as PhoPR which we found to be under strong evolutionary pressure during human lung infection. We show that PhoPR is activated at acidic pH and serves to regulate a defined set of genes involved in host adaptation. Accordingly, clinical isolates from chronically infected human lungs tend to hyperactivate this regulator enabling M. abscessus to escape macrophage killing.

Mycobacterium tuberculosis response to cholesterol is integrated with environmental pH and potassium levels via a lipid utilization regulator.

How bacterial response to environmental cues and nutritional sources may be integrated in enabling host colonization is poorly understood. Exploiting a reporter-based screen, we discovered that overexpression of Mycobacterium tuberculosis (Mtb) lipid utilization regulators altered Mtb acidic pH response dampening by low environmental potassium (K+). Transcriptional analyses unveiled amplification of Mtb response to acidic pH in the presence of cholesterol, a major carbon source for Mtb during infection, and vice versa. Strikingly, deletion of the putative lipid regulator mce3R resulted in loss of augmentation of (i) cholesterol response at acidic pH, and (ii) low [K+] response by cholesterol, with minimal effect on Mtb response to each signal individually. Finally, the ∆mce3R mutant was attenuated for colonization in a murine model that recapitulates lesions with lipid-rich foamy macrophages. These findings reveal critical coordination between bacterial response to environmental and nutritional cues, and establish Mce3R as a crucial integrator of this process.