Characterization of nitrite degradation by Lactobacillus casei subsp. rhamnosus LCR 6013

Diverse mechanisms by which chemical pollutant exposure alters gut microbiota metabolism and inflammation

The human gut microbiome, the host, and the environment are inextricably linked across the life course with significant health impacts. Consisting of trillions of bacteria, fungi, viruses, and other micro-organisms, microbiota living within our gut are particularly dynamic and responsible for digestion and metabolism of diverse classes of ingested chemical pollutants. Exposure to chemical pollutants not only in early life but throughout growth and into adulthood can alter human hosts' ability to absorb and metabolize xenobiotics, nutrients, and other components critical to health and longevity. Inflammation is a common mechanism underlying multiple environmentally related chronic conditions, including cardiovascular disease, multiple cancer types, and mental health. While growing research supports complex interactions between pollutants and the gut microbiome, significant gaps exist. Few reviews provide descriptions of the complex mechanisms by which chemical pollutants interact with the host microbiome through either direct or indirect pathways to alter disease risk, with a particular focus on inflammatory pathways. This review focuses on examples of several classes of pollutants commonly ingested by humans, including (i) heavy metals, (ii) persistent organic pollutants (POPs), and (iii) nitrates. Digestive enzymes and gut microbes are the first line of absorption and metabolism of these chemicals, and gut microbes have been shown to alter compounds from a less to more toxic state influencing subsequent distribution and excretion. In addition, chemical pollutants may interact with or alter the selection of more harmful and less commensal microbiota, leading to gut dysbiosis, and changes in receptor-mediated signaling pathways that alter the integrity and function of the gut intestinal tract. Arsenic, cadmium, and lead (heavy metals), influence the microbiome directly by altering different classes of bacteria, and subsequently driving inflammation through metabolite production and different signaling pathways (LPS/TLR4 or proteoglycan/TLR2 pathways). POPs can alter gut microbial composition either directly or indirectly depending on their ability to activate key signaling pathways within the intestine (e.g., PCB-126 and AHR). Nitrates and nitrites' effect on the gut and host may depend on their ability to be transformed to secondary and tertiary metabolites by gut bacteria. Future research should continue to support foundational research both in vitro, in vivo, and longitudinal population-based research to better identify opportunities for prevention, gain additional mechanistic insights into the complex interactions between environmental pollutants and the microbiome and support additional translational science.

Fermented Vegetables: Health Benefits, Defects, and Current Technological Solutions

This review summarizes current studies on fermented vegetables, analyzing the changes in nutritional components during pickling, the health benefits of fermented vegetables, and their safety concerns. Additionally, the review provides an overview of the applications of emergent non-thermal technologies for addressing these safety concerns during the production and processing of fermented vegetables. It was found that vitamin C would commonly be lost, the soluble protein would degrade into free amino acids, new nutrient compositions would be produced, and the flavor correlated with the chemical changes. These changes would be influenced by the variety/location of raw materials, the original bacterial population, starter cultures, fermentation conditions, seasoning additions, and post-fermentation processing. Consuming fermented vegetables benefits human health, including antibacterial effects, regulating intestinal bacterial populations, and promoting health (anti-cancer effects, anti-diabetes effects, and immune regulation). However, fermented vegetables have chemical and biological safety concerns, such as biogenic amines and the formation of nitrites, as well as the existence of pathogenic microorganisms. To reduce hazardous components and control the quality of fermented vegetables, unique starter cultures, high pressure, ultrasound, cold plasma, photodynamic, and other technologies can be used to solve these problems.

Cold Plasma Controls Nitrite Hazards by Modulating Microbial Communities in Pickled Radish

The hazard of nitrite caused by microorganisms is the main food safety problem in the pickle production. To seek a method to control the nitrite hazards of pickles by regulating microbial community without additional substances, we focused on cold plasma because Gram-negative and Gram-positive bacteria have different degrees of sensitivity to the sterilization of cold plasma. Using radish pickles as the experimental object, based on colony counting, dynamic monitoring of pH and nitrite, qPCR and high-throughput sequencing, it was found that when the raw material was treated with dielectric barrier discharge (DBD) cold plasma at 40 kV for 60 s, Gram-negative bacteria with the potential to produce nitrite were preferentially sterilized. Meanwhile, Gram-positive bacteria dominated by the lactic acid bacteria were retained to accelerate the acid production rate, initiate the self-degradation of nitrite in advance and significantly reduce the peak value and accumulation of nitrite during the fermentation process of pickled radish. This study preliminarily verified that DBD cold plasma can inhibit the nitrite generation and accelerate the self-degradation of nitrite by regulating the structure and abundance of microbial community in radish pickles, which provides an important reference for the control of nitrite hazards in the fermentation process of pickles without additives.

N-nitrosamines in Qingdao dried aquatic products and dietary risk assessment

N-nitrosamines are human carcinogens commonly present in dried aquatic products. A method of gas chromatography - mass spectrometry combined with steam distillation was developed for the determination of 9 N-nitrosamines in dried aquatic products in Qingdao, China, with which 300 samples of fish, squid, shrimp and sea cucumber collected from Qingdao were analysed. A health risk assessment was conducted based on determined levels of N-nitrosamines by using estimated daily intake and slope factors. Results showed that fish products was the category with the highest content of N-nitrosamines, whereas squid and shrimp products were the categories with the highest frequency of presence of N-nitrosamines. The average estimated cancer risk of N-nitrosamines in dried aquatic products in Qingdao ranged from 3.57 × 10^-8 to 3.53 × 10^-5. Nitrosodimethylamine, N-Nitrosodiethylamine and N-Nitrosodibutylamine could be considered to pose a potential cancer risk to residents in Qingdao.

Regulation of Nir gene in Lactobacillus plantarum WU14 mediated by GlnR

Nitrogen (N) is an essential element in the biosynthesis of key cellular components, such as proteins and nucleic acids, in all living organisms. Nitrite, as a form of nitrogen utilization, is the main nutrient for microbial growth. However, nitrite is a potential carcinogen that combines with secondary amines, which are breakdown products of proteins, to produce N-nitroso compounds that are strongly carcinogenic. Nitrite reductase (Nir) produced by microorganisms can reduce nitrite. Binding of GlnR to the promoter of nitrogen metabolism gene can regulate the expression of Nir operon. In this study, nitrite-resistant Lactobacillus plantarum WU14 was isolated from Pickles and its protease Nir was analyzed. GlnR-mediated regulation of L. plantarum WU14 Nir gene was investigated in this study. New GlnR and Nir genes were obtained from L. plantarum WU14. The regulation effect of GlnR on Nir gene was examined by gel block test, yeast two-hybrid system, bacterial single hybrid system and qRT-RCR. Detailed analysis showed that GlnR ound to the Nir promoter region and interacted with Nir at low nitrite concentrations, positively regulating the expression of NIR. However, the transcription levels of GlnR and Nir decreased gradually with increasing nitrite concentration. The results of this study improve our understanding of the function of the Nir operon regulatory system and serve as the ground for further study of the signal transduction pathway in lactic acid bacteria.

Mesoporous CoOx/C Nanocomposites Functionalized Electrochemical Sensor for Rapid and Continuous Detection of Nitrite

Nitrite is widespread in the environment, and is frequently used as an additive to extend the shelf life of meat products. However, the excess intake of nitrite can be harmful to human health. Hence, it is very important to know and control the content of nitrite in foodstuffs. In this work, by the means of self-assembly induced by solvent evaporation, we used the amphiphilic PEO-b-PS diblock copolymers resol and cobalt nitrate as a template to synthesize ordered mesoporous CoOx/C nanocomposites. Then, the CoOx/C nanocomposites were modified on a glassy carbon electrode (GCE), which showed excellent sensitivity, good selectivity, and a wide detection range for nitrite. Through cyclic voltammetry and current–time techniques, the electrochemical performance of the GCE modified with CoOx/C nanocomposites was analyzed. Under the optimized conditions, we found that anodic currents were linearly related to nitrite concentrations with a regression equation of lp (µA) = 0.36388 + 0.01616C (R2 = 0.9987) from 0.2 µM to 2500 µM, and the detection limit was 0.05 µM. Furthermore, the electrochemical sensor behaved with high reproducibility and anti-interference ability towards various organic and inorganic ions, such as NO3−, SO42−, Cl−, COOH− (Ac−), Na+, K+, Mg2+, and NH4+. Our results indicated that these CoOx/C nanocomposites could be applied in electrochemical sensors for the rapid and sensitive detection of the food preservative nitrite.

Isolation, expression, and biochemical characterization: nitrite reductase from Bacillus cereus LJ01

Biological remediation of toxic oxygen-containing anions such as nitrate that are common in the environment is of great significance. Therefore, it is necessary to understand the specific role of nitrate and nitrite reductase in the bioremediation process. Bacillus cereus LJ01, which was isolated from traditional Chinese soybean paste, effectively degraded nitrite (such as NaNO₂) at 0–15 mmol L⁻¹ in LB medium. Moreover, the nitrite-degrading active substance (ASDN) was isolated and purified from B. cereus LJ01. The nitrite-degrading activity of nitrite reductase (named LJ01-NiR) was 4004.89 U mg⁻¹. The gene encoding the assimilation of nitrite reductase in B. cereus LJ01 was cloned and overexpressed in E. coli. The purified recombinant LJ01-NiR has a wide range of activities under temperature (20–60 °C), pH (6.5–8.0) and metal ions (Fe³⁺, Fe²⁺, Cu²⁺, Mn²⁺, and Al³⁺). Kinetic parameters of LJ01-NiR, including the values of K_m and V_max were 1.38 mM and 2.00 μmol g⁻¹ min⁻¹, respectively. The results showed that LJ01-NiR could degrade nitrite with or without an electron donor. In addition, sequence analysis revealed that LJ01-NiR was a ferredoxin-dependent nitrite reductase given the presence of conserved [Fe4–S4] cluster and heme-binding domain. The nitrite ion binds to the LJ01-NiR active site by forming three hydrogen bonds with the residues ASN72, ALA133 and ASN140. Due to its high nitrite-degrading activity, LJ01-NiR could potentially be used for environmental pollution treatment.

Biological remediation of toxic oxygen-containing anions such as nitrite in the environment is of great significance. Bacillus cereus LJ01 showed the activity of degradation for nitrite. the enzyme NiR from LJ01 can degrade the nitrite in vitro.

Recipe for a Healthy Gut: Intake of Unpasteurised Milk Is Associated with Increased Lactobacillus Abundance in the Human Gut Microbiome

INTRODUCTION

The gut microbiota plays a role in gut-brain communication and can influence psychological functioning. Diet is one of the major determinants of gut microbiota composition. The impact of unpasteurised dairy products on the microbiota is unknown. In this observational study, we investigated the effect of a dietary change involving intake of unpasteurised dairy on gut microbiome composition and psychological status in participants undertaking a residential 12-week cookery course on an organic farm.

METHODS

Twenty-four participants completed the study. The majority of food consumed during their stay originated from the organic farm itself and included unpasteurised milk and dairy products. At the beginning and end of the course, participants provided faecal samples and completed self-report questionnaires on a variety of parameters including mood, anxiety and sleep. Nutrient intake was monitored with a food frequency questionnaire. Gut microbiota analysis was performed with 16S rRNA gene sequencing. Additionally, faecal short chain fatty acids (SCFAs) were measured.

RESULTS

Relative abundance of the genus Lactobacillus increased significantly between pre- and post-course time points. This increase was associated with participants intake of unpasteurised milk and dairy products. An increase in the faecal SCFA, valerate, was observed along with an increase in the functional richness of the microbiome profile, as determined by measuring the predictive neuroactive potential using a gut-brain module approach.

CONCLUSIONS

While concerns in relation to safety need to be considered, intake of unpasteurised milk and dairy products appear to be associated with the growth of the probiotic bacterial genus, Lactobacillus, in the human gut. More research is needed on the effect of dietary changes on gut microbiome composition, in particular in relation to the promotion of bacterial genera, such as Lactobacillus, which are recognised as being beneficial for a range of physical and mental health outcomes.

Effect of selenium supplements on the antioxidant activity and nitrite degradation of lactic acid bacteria

Selenium (Se) is one of the essential trace elements in the human body, and Se-enriched lactic acid bacteria (LAB) can improve the biological utilization value of inorganic Se. The aim of this study was to isolate Se-enriched LAB and study their effects on antioxidant activity and nitrite degradation. The Se-enriched LAB L.P2, which was nitrite-tolerant and could grow in 30 µg/mL sodium selenite (Na₂SeO₃) medium, was isolated from the traditional fermented Chinese sauerkraut. L.P2 belonged to Lactobacillus plantarum according to the 16S rDNA analysis. The biomass and lactic acid production of L.P2 reached to a maximum (9.52 log CFU/mL and 16.99 mg/mL) when 2.0 µg/mL Na₂SeO₃ was supplemented in the medium. Additionally, the nitrite degradation rate reached 85.76% when the initial concentration of Na₂SeO₃ was 2.0 µg/mL. The Se-enriched LAB enhanced the scavenging capacity of hydroxyl radical and superoxide free radical of L.P2 and improved the lipid peroxidation and ion-chelating abilities. Moreover, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in Se 4 group (4.0 µg/mL Na₂SeO₃ was added) reached 48.49 and 50.35 U/mg, respectively. Thus, Se 4 concentration was significantly higher than that of Se 0 group (with no Se added). In particular, SOD and GSH-Px enzymes correlated with nitrite degradation (P < 0.01). Collectively, our results indicate that Se supplementation can enhance the antioxidant capacity of LAB, contribute to its nitrite degradation, and thus may have potential applications in functional foods.

Evaluation of the impact on food safety of a Lactobacillus coryniformis strain from pickled vegetables with degradation activity against nitrite and other undesirable compounds

Four strains of lactic acid bacteria showing antimicrobial activity against some food-spoilage microorganisms or pathogens, including both Gram-negative and -positive strains, were isolated from naturally fermented pickled vegetables and a traditional cheese product. Among these isolates, Lactobacillus coryniformis strain BBE-H3, characterised previously to be a non-biogenic amine producer, showed a high level of activity in degrading sodium nitrite and exhibited the ability to eliminate ethyl carbamate and one of its precursors, urea. The antimicrobial substance produced by L. coryniformis BBE-H3 was found to be active at an acidic pH range of 4.0-4.5. The antimicrobial activity of this strain decreased differentially after treatment with proteolytic enzymes (pepsin, papain, trypsin and proteinase K), implying this growth inhibitory compound is either a protein or a polypeptide. The results of this study show the suitability of L. coryniformis BBE-H3 as a starter in food manufacturing processes, and demonstrate its potential role in eliminating food origin carcinogens such as sodium nitrite and ethyl carbamate.