Disruption of Lactobacillus delbrueckii ssp. bulgaricus 11842 cells for lactose hydrolysis in dairy products: a comparison of sonication, high-pressure homogenization and bead milling

Probiotics and Paraprobiotics: Effects on Microbiota-Gut-Brain Axis and Their Consequent Potential in Neuropsychiatric Therapy

Neuropsychiatric disorders are clinical conditions that affect cognitive function and emotional stability, often resulting from damage or disease in the central nervous system (CNS). These disorders are a worldwide concern, impacting approximately 12.5% of the global population. The gut microbiota has been linked to neurological development and function, implicating its involvement in neuropsychiatric conditions. Due to their interaction with gut microbial communities, probiotics offer a natural alternative to traditional treatments such as therapeutic drugs and interventions for alleviating neuropsychiatric symptoms. Introduced by Metchnikoff in the early 1900s, probiotics are live microorganisms that provide various health benefits, including improved digestion, enhanced sleep quality, and reduced mental problems. However, concerns about their safety, particularly in immunocompromised patients, warrant further investigation; this has led to the concept of "paraprobiotics", inactivated forms of beneficial microorganisms that offer a safer alternative. This review begins by exploring different methods of inactivation, each targeting specific cellular components like DNA or proteins. The choice of inactivation method is crucial, as the health benefits may vary depending on the conditions employed for inactivation. The subsequent sections focus on the potential mechanisms of action and specific applications of probiotics and paraprobiotics in neuropsychiatric therapy. Probiotics and paraprobiotics interact with gut microbes, modulating the gut microbial composition and alleviating gut dysbiosis. The resulting neuropsychiatric benefits primarily stem from the gut-brain axis, a bidirectional communication channel involving various pathways discussed in the review. While further research is needed, probiotics and paraprobiotics are promising therapeutic agents for the management of neuropsychiatric disorders.

The Synthesis, Characterization and Applications of Polyhydroxyalkanoates (PHAs) and PHA-Based Nanoparticles

Polyhydroxyalkanoates (PHAs) are storage granules found in bacteria that are essentially hydroxy fatty acid polyesters. PHA molecules appear in variety of structures, and amongst all types of PHAs, polyhydroxybutyrate (PHB) is used in versatile fields as it is a biodegradable, biocompatible, and ecologically safe thermoplastic. The unique physicochemical characteristics of these PHAs have made them applicable in nanotechnology, tissue engineering, and other biomedical applications. In this review, the optimization, extraction, and characterization of PHAs are described. Their production and application in nanotechnology are also portrayed in this review, and the precise and various production methods of PHA-based nanoparticles, such as emulsion solvent diffusion, nanoprecipitation, and dialysis are discussed. The characterization techniques such as UV-Vis, FTIR, SEM, Zeta Potential, and XRD are also elaborated.

Effects of Sub-Lethal High Pressure Homogenization Treatment on the Adhesion Mechanisms and Stress Response Genes in Lactobacillus acidophilus 08

Cell surface hydrophobicity (CSH) and adhesion are very important phenotypical traits for probiotics that confer them a competitive advantage for the resilience in the human gastrointestinal tract. This study was aimed to understand the effects over time of a 50 MPa hyperbaric treatment on the surface properties of Lactobacillus acidophilus 08 including CSH, autoaggregation, and in vitro adhesion (mucin layer and Caco-2 cells). Moreover, a link between the hurdle applied and the expression of genes involved in the general stress response (groEL and clpP) and adhesion processes (efTu and slpA) was evaluated. High pressure homogenization (HPH) at 50 MPa significantly increased the CSH percentage (H%), autoaggregation and in vitro adhesion on mucin of L. acidophilus 08 cells compared with the untreated cells. Moreover, the hyperbaric hurdle induced an upregulation of the stress response genes groEL and ef-TU together with a down regulation of the clpP and S-layer slpA genes. Looking at the protein profile, HPH-treatment showed an increase in the number or intensity of protein bands at high and low molecular weights.

Effects of ccpA gene deficiency in Lactobacillus delbrueckii subsp. bulgaricus under aerobic conditions as assessed by proteomic analysis

Background

Aerobic growth provides benefits in biomass yield and stress tolerance of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). Catabolite control protein A (CcpA) is a master regulator involved in the aerobic and anaerobic growth, metabolic production and stress response in L. bulgaricus, but its potential molecular mechanisms remains unclear. The aim of this study is to elucidate the role of CcpA in L. bulgaricus in aerobic growth at the proteomic perspective.

Results

The differential proteomic analysis was performed on the L. bulgaricus ATCC11842 and its ccpA inactivated mutant strain using iTRAQ technology. A total of 132 differentially expressed proteins were obtained, among which 58 were up-regulated and 74 were down-regulated. These proteins were mainly involved in the cellular stress response, carbohydrate and energy metabolism, amino acid transport and protein synthesis, genetic information processing. Moreover, inactivation of ccpA negatively affected the expression of key enzymes involved in glycolysis pathway, while it enhanced the expression of proteins related to the pyruvate pathway, supporting the conclusion that CcpA mediated the shift from homolactic fermentation to mixed acid fermentation in L. bulgaricus.

Conclusions

Overall, these results showed that the role of CcpA in L. bulgaricus as a pleiotropic regulator in aerobic metabolism and stress response. This proteomic analysis also provide new insights into the CcpA-mediated regulatory network of L. bulgaricus and potential strategies to improve the production of starter and probiotic cultures based on the metabolic engineering of global regulators.

Microscale disruption of microorganisms for parallelized process development

Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris are the standard platforms for biopharmaceutical production with 40% of all between 2010 to 2014 approved protein drugs produced in those microbial hosts. Typically, products overexpressed E. coli and S. cerevisiae remain in the cytosol or are secreted into the periplasm. Consequently, efficient cell disruption is essential for high product recovery during microbial production. Process development platforms at microscale are essential to shorten time to market. While high-pressure homogenization is the industry standard for cell disruption at large scale this method is not practicable for experiments in microscale. This review describes microscale methods for cell disruption at scales as low as 200 µL. Strategies for automation, parallelization and miniaturization, as well as comparability of the results at this scale to high pressure homogenization are considered as those criteria decide which methods are most suited for scale down. Those aspects are discussed in detail for protein overexpression in E. coli and yeast but also the relevance for alternative products and host such as microalgae are taken into account. The authors conclude that bead milling is the best comparable microscale method to large scale high-pressure homogenization and therefore the most suitable technique for automated process development of microbial hosts with the exception of pDNA production.

Tea polyphenol epigallocatechin gallate inhibits Escherichia coli by increasing endogenous oxidative stress

The antibacterial effects of tea polyphenol epigallocatechin gallate (EGCG), a common phytochemical with a number of potential health benefits, are well known. However, the mechanism of its bactericidal action remains unclear. Using E. coli as a model organism, it is argued here that H2O2 synthesis by EGCG is not attributed to its inhibitory effects. In contrast, the bactericidal action of EGCG was a result of increased intracellular reactive oxygen species and blunted adaptive oxidative stress response in E. coli due to the co-administration of antioxidant N-acetylcysteine, and not on account of exogenous catalase. Furthermore, we noted a synergistic bactericidal effect for EGCG when combined with paraquat. However, under anaerobic conditions, the inhibitory effect of EGCG was prevented. In conclusion, EGCG caused an increase in endogenous oxidative stress in E. coli, thereby inhibiting its growth, and hence the use of EGCG as a prooxidant is supported by this study.

Cell membrane fatty acid changes and desaturase expression of Saccharomyces bayanus exposed to high pressure homogenization in relation to the supplementation of exogenous unsaturated fatty acids

Aims: The aim of this work was to study the responses of Saccharomyces bayanus cells exposed to sub-lethal high-pressure homogenization (HPH) and determine whether the plasmatic membrane can sense HPH in the presence, or absence, of exogenous unsaturated fatty acids (UFAs) in the growth medium.

Methods and Results: High-pressure homogenization damaged and caused the collapse of cell walls and membranes of a portion of cells; however, HPH did not significantly affect S. bayanus cell viability (less than 0.3 Log CFU ml^-1). HPH strongly affected the membrane fatty acid (FA) composition by increasing the percentage of total UFA when compared with saturated fatty acids. The gene expression showed that the transcription of OLE1, ERG3, and ERG11 increased after HPH. The presence of exogenous UFA abolished HPH-induced effects on the OLE1 and ERG3 genes, increased the percentage of membrane lipids and decreased the expression of OLE1 and ERG3 within 30 min of treatment.

Conclusion: The results suggest a key role for UFA in the microbial cell response to sub-lethal stress. In addition, these data provide insight into the molecular basis of the response of S. bayanus to this innovative technology.

Significance and Impact of the Study: Elucidation of the mechanism of action for sub-lethal HPH will enable the utilization of this technology to modulate the starter performance at the industrial scale.

Effects of sub-lethal high-pressure homogenization treatment on the outermost cellular structures and the volatile-molecule profiles of two strains of probiotic lactobacilli

Applying sub-lethal levels of high-pressure homogenization (HPH) to lactic acid bacteria has been proposed as a method of enhancing some of their functional properties. Because the principal targets of HPH are the cell-surface structures, the aim of this study was to examine the effect of sub-lethal HPH treatment on the outermost cellular structures and the proteomic profiles of two known probiotic bacterial strains. Moreover, the effect of HPH treatment on the metabolism of probiotic cells within a dairy product during its refrigerated storage was investigated using SPME-GC-MS. Transmission electron microscopy was used to examine the microstructural changes in the outermost cellular structures due to HPH treatment. These alterations may be involved in the changes in some of the technological and functional properties of the strains that were observed after pressure treatment. Moreover, the proteomic profiles of the probiotic strains treated with HPH and incubated at 37°C for various periods showed different peptide patterns compared with those of the untreated cells. In addition, there were differences in the peaks that were observed in the low-mass spectral region (2000–3000 Da) of the spectral profiles of the control and treated samples. Due to pressure treatment, the volatile-molecule profiles of buttermilk inoculated with treated or control cells and stored at 4°C for 30 days exhibited overall changes in the aroma profile and in the production of molecules that improved its sensory profile, although the two different species imparted specific fingerprints to the product. The results of this study will contribute to understanding the changes that occur in the outermost cellular structures and the metabolism of LAB in response to HPH treatment. The findings of this investigation may contribute to elucidating the relationships between these changes and the alterations of the technological and functional properties of LAB induced by pressure treatment.

Overall Key Performance Indicator to Optimizing Operation of High-Pressure Homogenizers for a Reliable Quantification of Intracellular Components in Pichia pastoris

The most commonly used cell disruption procedures may present lack of reproducibility, which introduces significant errors in the quantification of intracellular components. In this work, an approach consisting in the definition of an overall key performance indicator (KPI) was implemented for a lab scale high-pressure homogenizer (HPH) in order to determine the disruption settings that allow the reliable quantification of a wide sort of intracellular components. This innovative KPI was based on the combination of three independent reporting indicators: decrease of absorbance, release of total protein, and release of alkaline phosphatase activity. The yeast Pichia pastoris growing on methanol was selected as model microorganism due to it presents an important widening of the cell wall needing more severe methods and operating conditions than Escherichia coli and Saccharomyces cerevisiae. From the outcome of the reporting indicators, the cell disruption efficiency achieved using HPH was about fourfold higher than other lab standard cell disruption methodologies, such bead milling cell permeabilization. This approach was also applied to a pilot plant scale HPH validating the methodology in a scale-up of the disruption process. This innovative non-complex approach developed to evaluate the efficacy of a disruption procedure or equipment can be easily applied to optimize the most common disruption processes, in order to reach not only reliable quantification but also recovery of intracellular components from cell factories of interest.

Production of β-galactosidase from streptococcus thermophilus for galactooligosaccharides synthesis

Efficiency of different methods for disruption of Streptococcus thermophilus cells, isolated from different dairy products, to release β-galactosidase and synthesis of GOS by extracted enzyme using whey supplemented with different concentrations of lactose as a substrate was studied. Unlike most other studies on GOS synthesis which used only one method of cell disruption and only few microbial strains, we compared five different cell disruption methods and used 30 strains of S. thermophilus in order to find out the most effective method and efficient strain for production of β-galactosidase. Appreciable amount of GOS (53.45 gL(-1)) was synthesized at a lactose concentration of 30 %, using enzyme (10 U mL(-1) of reaction medium), extracted from S. thermophilus within a very short incubation time of 5 h at a temperature of 40 °C and pH 6.8. S. thermophilus is heavily employed in the preparation of fermented dairy products but this study extends the use of this organism for the production of GOS, a potential prebiotic.

Studies on the lipolytic activity of sonicated enzymes from Yarrowia lipolytica

The aim of this study was to evaluate the efficiency of sonication in releasing protein from a widespread lipase-producing yeast, Yarrowia lipolytica KKP 379, and to examine the impact of ultrasound waves generated in a horn-type sonicator on the lipolytic activity of Y. lipolytica in the hydrolysis of p-nitrophenyl laurate. In this paper, we focused on a few parameters of ultrasound cell disruption, such as the time of sonication, acoustic power, storage time of the frozen yeast biomass used in sonication and the solvent used to suspend the yeast cells which were considered as the most important part in the process of obtaining a biocatalyst from Y. lipolytica for organic synthesis. The most effective additive in protein release proved to be 2% Tween 80; other ideal parameters of the process were ultrasonic power at 150 W for 15 min and 9 weeks of frozen biomass storage time. The sonication parameters, which were the best for protein release, did not seem to be the most effective for obtaining high lipolytic activity due to denaturation as an effect of cavitation.

Potential Applications of Immobilized β-Galactosidase in Food Processing Industries

The enzyme β-galactosidase can be obtained from a wide variety of sources such as microorganisms, plants, and animals. The use of β-galactosidase for the hydrolysis of lactose in milk and whey is one of the promising enzymatic applications in food and dairy processing industries. The enzyme can be used in either soluble or immobilized forms but the soluble enzyme can be used only for batch processes and the immobilized form has the advantage of being used in batch wise as well as in continuous operation. Immobilization has been found to be convenient method to make enzyme thermostable and to prevent the loss of enzyme activity. This review has been focused on the different types of techniques used for the immobilization of β-galactosidase and its potential applications in food industry.

Effect of a pre-treatment of milk with high pressure homogenization on yield as well as on microbiological, lipolytic and proteolytic patterns of "Pecorino" cheese

The principal aim of this work was to compare Pecorino cheeses obtained from ewes' milk previously subjected to high pressure homogenization (HPH) at 100 MPa with those produced from raw and heat treated ewes' milk. The HPH milk treatment induced a significant increase of the cheese yield and caused a reduction of enterococci, lactococci and yeasts in the curds. Enterococci cell loads remained at lower levels in cheeses obtained from HPH milk over the ripening period. Analyses of free fatty acids, Sodium Dodecil Sulphate (SDS)-PAGE profiles, Gas Chromatography-Mass Spectrometry-Solid Phase Microextraction (GC-MS-SPME) measurements of volatile compounds and sensory traits evidenced that the pressure treatment can be regarded also as a useful tool to differentiate products obtained from the same raw material. In fact such a milk treatment induced a marked lipolysis, an early proteolysis, a relevant modification of the volatile molecule profiles and sensory properties of Pecorino cheese.

Bioassay-guided purification and identification of antimicrobial components in Chinese green tea extract

The Chinese green tea extract was found to strongly inhibit the growth of major food-borne pathogens, Escherichia coli O157:H7, Salmonella Typhimurium DT104, Listeria monocytogenes, Staphylococcus aureus, and a diarrhoea food-poisoning pathogen Bacillus cereus, by 44-100% with the highest activity found against S. aureus and lowest against E. coli O157:H7. A bioassay-guided fractionation technique was used for identifying the principal active component. A simple and efficient reversed-phase high-speed counter-current chromatography (HSCCC) method was developed for the separation and purification of four bioactive polyphenol compounds, epicatechin gallate (ECG), epigallocatechin gallate (EGCG), epicatechin (EC), and caffeine (CN). The structures of these polyphenols were confirmed with mass spectrometry. Among the four compounds, ECG and EGCG were the most active, particularly EGCG against S. aureus. EGCG had the lowest MIC90 values against S. aureus (MSSA) (58 mg/L) and its methicilin-resistant S. aureus (MRSA) (37 mg/L). Scanning electron microscopy (SEM) studies showed that these two compounds altered bacterial cell morphology, which might have resulted from disturbed cell division. This study demonstrated a direct link between the antimicrobial activity of tea and its specific polyphenolic compositions. The activity of tea polyphenols, particularly EGCG on antibiotics-resistant strains of S. aureus, suggests that these compounds are potential natural alternatives for the control of bovine mastitis and food poisoning caused by S. aureus.