The ability of biogenic amines and ammonia production by single bacterial cultures

Roux-en-Y gastric bypass-associated fecal tyramine promotes colon cancer risk via increased DNA damage, cell proliferation, and inflammation

BACKGROUND

Fecal abundances of Enterobacteriaceae and Enterococcaceae are elevated in patients following Roux-en-Y gastric bypass (RYGB) surgery. Concurrently, fecal concentrations of tyramine, derived from gut bacterial metabolism of tyrosine and/or food, increased post-RYGB. Furthermore, emerging evidence suggests that RYGB is associated with increased colorectal cancer (CRC) risk. However, the causal link between RYGB-associated microbial metabolites and CRC risk remains unclear. Hence, this study investigated the tyrosine metabolism of Enterobacteriaceae and Enterococcaceae strains isolated from patients post-RYGB and explored the causal effects of tyramine on the CRC risk and tumorigenesis using both human colonic cancer cell line (HCT 116) and wild-type and ApcMin/+ mice.

RESULTS

We isolated 31 bacterial isolates belonging to Enterobacteriaceae and Enterococcaceae families from the feces of patients with RYGB surgery. By culturing the isolates in tyrosine-supplemented medium, we found that Citrobacter produced phenol as a main product of tyrosine, whereas Enterobacter and Klebsiella produced 4-hydroxyphenylacetate, Escherichia produced 4-hydroxyphenyllactate and 4-hydroxyphenylpyruvate, and Enterococcus and two Klebsiella isolates produced tyramine. These observations suggested the gut bacterial contribution to increased fecal concentrations of tyramine post-RYGB. We subsequently evaluated the impact of tyramine on CRC risk and development. Tyramine induced necrosis and promoted cell proliferation and DNA damage of HCT 116 cells. Daily oral administration of tyramine for 49 days to wild-type mice resulted in visible adenomas in 5 out of 12 mice, accompanied by significantly enhanced DNA damage (γH2AX +) and an increased trend of cell proliferation (Ki67 +) in the ileum, along with an upregulated expression of the cell division cycle gene (Cdc34b) in the colon. To evaluate the impact of tyramine on intestinal tumor growth, we treated ApcMin/+ mice with the same doses of tyramine and duration. These mice showed larger colonic tumor size and increased intestinal cell proliferation and inflammation (e.g., increased mRNA expression of IL-17A and higher number of Ly6G + neutrophils) compared to water-treated ApcMin/+ control mice.

CONCLUSIONS

Our results collectively suggested that RYGB-associated fecal bacteria could contribute to tyramine production and tyramine increased CRC risk by increasing DNA damage, cell proliferation, and pro-inflammatory responses of the gut. Monitoring and modulating tyramine concentrations in high-risk individuals could aid CRC prognosis and management. Video Abstract.

The development of a whole-cell biosensor enabled the identification of agmatine-producing Hafnia spp. in cheese

Agmatine, the decarboxylation product of arginine, is the precursor of putrescine - a harmful biogenic amine (BA) - that can accumulate in dairy products via bacterial metabolism involving the agmatine deiminase (AGDI) pathway. This first requires agmatine be produced via the decarboxylation of arginine and it remains unknown which microorganisms are responsible for this prior decarboxylation step. In addition, agmatine, as other BA, plays different physiological roles including those of co-transmitter and neuromodulator. Preclinical and clinical studies have shown agmatine to have a neuroprotective effect, rendering it of therapeutic interest being agmatine-producing bacteria proposed as psychobiotics. The identification of BA-producing microorganisms is based on the rise in pH due to the consumption of H+ during such decarboxylation reactions. However, in the detection of agmatine-producing microorganisms in cheese, this would lead to false positives since many bacteria possess arginine deiminase activity; this produces ornithine and ammonium from arginine, which also increases the pH. To overcome this problem, a whole-cell biosensor based on a previously developed agmatine-inducible transcription system was designed, and a protocol optimized for the successful identification of agmatine-producing microorganisms in cheese. The application of this protocol in cheese samples allowed for the isolation of agmatine-producing microorganisms identified as Hafnia spp. and unravels, for first time, the capacity of Hafnia paralvei to produce agmatine. This finding evidence the potential role of Hafnia spp. in putrescine accumulation in dairy products.

Bacteria-Triggered Mineralization of Silica Shells with Nanochannels for Biocatalysis in Harsh Conditions

Biocatalytic processes using microorganisms are considered efficient and economically and environmentally friendly reactions. However, the viability and function of these microorganisms are prone to being hindered by various practical environments. Here, we reported a bacteria-induced nanochannel structure that endowed the microorganism with biocatalytic ability in harsh conditions. We revealed that the bacteria could trigger the fusion of silica nanoparticles on their surface by the secreted alkaline metabolite, resulting in silica shells with nanochannels on bacteria (bacteria@nSiO2). The nanochannel structure in silica shells endowed bacteria with biocatalytic ability in multiple harsh conditions. We revealed that these nanochannels could influence the mass transfer from the extracellular to the intracellular environment, which protected the bacteria from excessive toxic substance while preserving the mass exchange during biocatalysis. This feature ensured bacteria@nSiO2 with efficient bioactivity under harsh conditions for industrial catalysis and degradation of pollution, which cannot be achieved by corresponding native bacteria. Using the crude oil spill as a practical example, we presented that bacteria@nSiO2 could degrade highly concentrated crude oil, which any reported bacteria cannot achieve. This work emphasized the role of nanochannels in the regulation of cellular functions for enhanced biocatalysis. It also demonstrated a bacteria-triggered nanostructure formation, which is a promising methodology for nanotechnology and provides a strategy for more advanced organism-material hybrids.

In vitro study of biogenic amine production and gastrointestinal stress tolerance by some enterococci strains

BACKGROUND

Owing to the toxic effects of enterococci, their biogenic amine production is a negative aspect of safe strain selection and unfavourable activity in food. Additionally, the ability to tolerate acid and bile are two important traits for the selection of probiotic strains since they show the probiotic bacteria's capacity to survive throughout gastrointestinal transit. In the present work, six enterococci strains belonging to Enterococcus gallinarum and Enterococcus hirae were subjected to in vitro evaluation of their ability to produce biogenic amines and to tolerate gastrointestinal stress in order to investigate their possibility for future intended use as probiotics.

RESULTS

All enterococci isolates possessed good viability at low pH (pH 4) and in the presence of bile salts (0.3%), indicating their ability to survive passage through the gastrointestinal tract. In addition, selected strains had a high ability to produce tyramine in tyrosine decarboxylase broth, while medium levels of histamine were detected (below 74 mg L-1 ) in experimental media in vitro. Other biogenic amines were also formed at various levels by most of the enterococci strains.

CONCLUSION

All enterococci strains, with the exception of E. gallinarum DM 29, are powerful tyramine producers, and their capacity to create histamine is inferior to that of tyramine. However, more investigations are needed before considering their use as bio-preservatives or starter cultures in foods. © 2023 Society of Chemical Industry.

Acidic Neutralization by Indigenous Bacteria Isolated from Abandoned Mine Areas

Soil acidification has been a serious problem in abandoned mine areas, and could be exacerbated by acid deposition with the release of mine wastes. In this study, three different indigenous bacterial consortia were isolated from abandoned mines in South Korea, from which the potential for acid neutralization of microorganisms was evaluated. They were all able to neutralize acidity within 24 h in the liquid nutrient medium. Moreover, a strong positive correlation (R = +0.922, p < 0.05) was established between the ammonium ion (NH4+) production yield and the resulting pH, indicating that NH4+ served as an important metabolite for biological neutralization. Serratialiquefaciens, Citrobacter youngae, Pseudescherichia vulneris, and Serratia grimesii had higher acid neutralization ability to generate NH4+ by the metabolism of nitrogen compounds such as carboxylation and urea hydrolysis. Therefore, acidic soils can be expected to be ameliorated by indigenous microorganisms through in situ biostimulation with the adequate introduction of nitrogenous substances into the soil environments.

Breathomics profiling of metabolic pathways affected by major depression: Possibilities and limitations

BACKGROUND

Major depressive disorder (MDD) is one of the most common psychiatric disorders with multifactorial etiologies. Metabolomics has recently emerged as a particularly potential quantitative tool that provides a multi-parametric signature specific to several mechanisms underlying the heterogeneous pathophysiology of MDD. The main purpose of the present study was to investigate possibilities and limitations of breath-based metabolomics, breathomics patterns to discriminate MDD patients from healthy controls (HCs) and identify the altered metabolic pathways in MDD.

METHODS

Breath samples were collected in Tedlar bags at awakening, 30 and 60 min after awakening from 26 patients with MDD and 25 HCs. The non-targeted breathomics analysis was carried out by proton transfer reaction mass spectrometry. The univariate analysis was first performed by T-test to rank potential biomarkers. The metabolomic pathway analysis and hierarchical clustering analysis (HCA) were performed to group the significant metabolites involved in the same metabolic pathways or networks. Moreover, a support vector machine (SVM) predictive model was built to identify the potential metabolites in the altered pathways and clusters. The accuracy of the SVM model was evaluated by receiver operating characteristics (ROC) analysis.

RESULTS

A total of 23 differential exhaled breath metabolites were significantly altered in patients with MDD compared with HCs and mapped in five significant metabolic pathways including aminoacyl-tRNA biosynthesis (p = 0.0055), branched chain amino acids valine, leucine and isoleucine biosynthesis (p = 0.0060), glycolysis and gluconeogenesis (p = 0.0067), nicotinate and nicotinamide metabolism (p = 0.0213) and pyruvate metabolism (p = 0.0440). Moreover, the SVM predictive model showed that butylamine (p = 0.0005, p_FDR=0.0006), 3-methylpyridine (p = 0.0002, p_FDR = 0.0012), endogenous aliphatic ethanol isotope (p = 0.0073, p_FDR = 0.0174), valeric acid (p = 0.005, p_FDR = 0.0162) and isoprene (p = 0.038, p_FDR = 0.045) were potential metabolites within identified clusters with HCA and altered pathways, and discriminated between patients with MDD and non-depressed ones with high sensitivity (0.88), specificity (0.96) and area under curve of ROC (0.96).

CONCLUSION

According to the results of this study, the non-targeted breathomics analysis with high-throughput sensitive analytical technologies coupled to advanced computational tools approaches offer completely new insights into peripheral biochemical changes in MDD.

Antibiotics and the Nervous System-Which Face of Antibiotic Therapy Is Real, Dr. Jekyll (Neurotoxicity) or Mr. Hyde (Neuroprotection)?

Antibiotics as antibacterial drugs have saved many lives, but have also become a victim of their own success. Their widespread abuse reduces their anti-infective effectiveness and causes the development of bacterial resistance. Moreover, irrational antibiotic therapy contributes to gastrointestinal dysbiosis, that increases the risk of the development of many diseases, including neurological and psychiatric. One of the potential options for restoring homeostasis is the use of oral antibiotics that are poorly absorbed from the gastrointestinal tract (e.g., rifaximin alfa). Thus, antibiotic therapy may exert neurological or psychiatric adverse drug reactions which are often considered to be overlooked and undervalued issues. Drug-induced neurotoxicity is mostly observed after beta-lactams and quinolones. Penicillin may produce a wide range of neurological dysfunctions, including encephalopathy, behavioral changes, myoclonus or seizures. Their pathomechanism results from the disturbances of gamma-aminobutyric acid-GABA transmission (due to the molecular similarities between the structure of the β-lactam ring and GABA molecule) and impairment of the functioning of benzodiazepine receptors (BZD). However, on the other hand, antibiotics have also been studied for their neuroprotective properties in the treatment of neurodegenerative and neuroinflammatory processes (e.g., Alzheimer's or Parkinson's diseases). Antibiotics may, therefore, become promising elements of multi-targeted therapy for these entities.

Time Evolution of Microbial Composition and Metabolic Profile for Biogenic Amines and Free Amino Acids in a Model Cucumber Fermentation System Brined with 0.5% to 5.0% Sodium Chloride

Salt concentrations in brine and temperature are the major environmental factors that affect activity of microorganisms and, thus may affect formation of biogenic amines (BAs) during the fermentation process. A model system to ferment cucumbers with low salt (0.5%, 1.5% or 5.0% NaCl) at two temperatures (11 or 23 °C) was used to study the ability of indigenous microbiota to produce biogenic amines and metabolize amino acid precursors. Colony counts for presumptive Enterococcus and Enterobacteriaceae increased by 4 and up to 2 log of CFU∙mL⁻¹, respectively, and remained viable for more than 10 days. 16S rRNA sequencing showed that Lactobacillus and Enterobacter were dominant in fermented cucumbers with 0.5% and 1.5% salt concentrations after storage. The initial content of BAs in raw material of 25.44 ± 4.03 mg∙kg⁻¹ fluctuated throughout experiment, but after 6 months there were no significant differences between tested variants. The most abundant BA was putrescine, that reached a maximum concentration of 158.02 ± 25.11 mg∙kg⁻¹. The Biogenic Amines Index (BAI) calculated for all samples was significantly below that needed to induce undesirable effects upon consumption. The highest value was calculated for the 23 °C/5.0% NaCl brine variant after 192 h of fermentation (223.93 ± 54.40). Results presented in this work indicate that possibilities to control spontaneous fermentation by changing salt concentration and temperature to inhibit the formation of BAs are very limited.

Construction of recombinant Escherichia coli producing nitrogenase-related proteins from Azotobacter vinelandii

Biological nitrogen fixation by nitrogenase has attracted attention as an alternative method to chemical nitrogen fixation, which requires large amounts of fossil fuels. Azotobacter vinelandii, which produces an oxygen-sensitive nitrogenase, can fix nitrogen even under aerobic conditions; therefore, the heterologous expression of nif-related genes from A. vinelandii is a promising strategy for developing a biological nitrogen fixation method. We assembled 17 nif-related genes, which are scattered throughout the genome of A. vinelandii, into synthetic gene clusters by overlap-extension-PCR and seamless cloning and expressed them in Escherichia coli. The transcription and translation of the 17 nif-related genes were evaluated by RT-qPCR and LC-MS/MS, respectively. The constructed E. coli showed nitrogenase activity under anaerobic and microaerobic conditions. This strain would be a useful model for examining the effect of other genes from A. vinelandii on nitrogen fixation by expressing them in addition to the minimal set of nif-related genes.

New Approaches to Profile the Microbiome for Treatment of Neurodegenerative Disease

Progressive neurodegenerative diseases represent some of the largest growing treatment challenges for public health in modern society. These diseases mainly progress due to aging and are driven by microglial surveillance and activation in response to changes occurring in the aging brain. The lack of efficacious treatment options for Alzheimer's disease (AD), as the focus of this review, and other neurodegenerative disorders has encouraged new approaches to address neuroinflammation for potential treatments. Here we will focus on the increasing evidence that dysbiosis of the gut microbiome is characterized by inflammation that may carry over to the central nervous system and into the brain. Neuroinflammation is the common thread associated with neurodegenerative diseases, but it is yet unknown at what point and how innate immune function turns pathogenic for an individual. This review will address extensive efforts to identify constituents of the gut microbiome and their neuroactive metabolites as a peripheral path to treatment. This approach is still in its infancy in substantive clinical trials and requires thorough human studies to elucidate the metabolic microbiome profile to design appropriate treatment strategies for early stages of neurodegenerative disease. We view that in order to address neurodegenerative mechanisms of the gut, microbiome and metabolite profiles must be determined to pre-screen AD subjects prior to the design of specific, chronic titrations of gut microbiota with low-dose antibiotics. This represents an exciting treatment strategy designed to balance inflammatory microglial involvement in disease progression with an individual's manifestation of AD as influenced by a coercive inflammatory gut.

Towards Understanding COVID-19: Molecular Insights, Co-infections, Associated Disorders, and Aging

BACKGROUND

COVID-19 can be related to any diseases caused by microbial infection(s) because 1) co-infection with COVID-19-related virus and other microorganism(s) and 2) because metabolites produced by microorganisms such as bacteria, fungi, and protozoan can be involved in necrotizing pneumonia and other necrotizing medical conditions observed in COVID-19.

OBJECTIVE

By way of illustration, the microbial metabolite of aromatic amino acid tryptophan, a biogenic amine tryptamine inducing neurodegeneration in cell and animal models, also induces necrosis.

METHODS

This report includes analysis of COVID-19 positivity by zip codes in Florida and relation of the positivity to population density, possible effect of ecological and social factors on spread of COVID-19, autopsy analysis of COVID-19 cases from around the world, serum metabolomics analysis, and evaluation of autoantigenome related to COVID-19.

RESULTS

In the present estimations, COVID-19 positivity percent per zip code population varied in Florida from 4.65% to 44.3% (February 2021 data). COVID-19 analysis is partially included in my book Microbial Metabolism and Disease (2021). The autoantigenome related to COVID-19 is characterized by alterations in protein biosynthesis proteins including aminoacyl-tRNA synthetases. Protein biosynthesis alteration is a feature of Alzheimer's disease. Serum metabolomics of COVID-19 positive patients show alteration in shikimate pathway metabolism, which is associated with the presence of Alzheimer's disease-associated human gut bacteria.

CONCLUSION

Such alterations in microbial metabolism and protein biosynthesis can lead to toxicity and neurodegeneration as described earlier in my book Protein Biosynthesis Interference in Disease (2020).

Volatile-Mediated Inhibitory Activity of Rhizobacteria as a Result of Multiple Factors Interaction: The Case of Lysobacter capsici AZ78

Plant beneficial rhizobacteria may antagonize soilborne plant pathogens by producing a vast array of volatile organic compounds (VOCs). The production of these compounds depends on the medium composition used for bacterial cell growth. Accordingly, Lysobacter capsici AZ78 (AZ78) grown on a protein-rich medium was previously found to emit volatile pyrazines with toxic activity against soilborne phypathogenic fungi and oomycetes. However, the discrepancy between the quantity of pyrazines in the gaseous phase and the minimum quantity needed to achieve inhibition of plant pathogens observed, lead us to further investigate the volatile-mediated inhibitory activity of AZ78. Here, we show that, besides VOCs, AZ78 cells produce ammonia in increased amounts when a protein-rich medium is used for bacterial growth. The production of this volatile compound caused the alkalinization of the physically separated culture medium where Rhizoctonia solani was inoculated subsequently. Results achieved in this work clearly demonstrate that VOC, ammonia and the growth medium alkalinization contribute to the overall inhibitory activity of AZ78 against R. solani. Thus, our findings suggest that the volatile-mediated inhibitory activity of rhizobacteria in protein-rich substrates can be regarded as a result of multiple factors interaction, rather than exclusively VOCs production.

Effect of Natural Zeolite (Clinoptilolite) on in vitro Biogenic Amine Production by Gram Positive and Gram Negative Pathogens

The effect of two levels of clinoptilolite (1 and 5%) on the production of biogenic amines (BA) and ammonia (AMN) by Gram positive (Staphylococcus aureus, Enterococcus faecalis, and Listeria monocytogenes) and Gram negative bacteria (Aeromonas hydrophila, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and Salmonella Parathypi A), in tyrosine decarboxylase broth (TDB) was studied. A. hydrophila and E. coli produced the highest amounts of amines which were 1223.06 and 2627.90 mg/l, respectively. All strains were able to decarboxylate tyrosine to tyramine (TYR) with E. coli being the highest (1657.19 mg/l). A. hydrophila formed >50 mg/l histamine (HIS) while the other strains produced none or very low concentrations (<4 mg/l). Among Gram-positive pathogens, E. faecalis was characterized as the main amine producer (478.23 mg/l). Although dependent on bacterial strain and level used, the natural zeolite clinoptilolite can be used to decrease BA and AMN production by bacterial strains that are of health concern. Practical Applications: Uses of natural prodcuts for biogenic amines inhibition. Clinoptilolite was used to reduce the amounts of amines such as spermine, putrescine, and dopamine produced by pathogenic and spoilage bacteria.

High Hydrostatic Pressure as a Tool to Reduce Formation of Biogenic Amines in Artisanal Spanish Cheeses

Two artisanal varieties of cheese made in Spain, one made of ewes' raw milk and the other of goats' raw milk were selected to evaluate the effect of a high hydrostatic pressure (HHP) treatment at 400 MPa during 10 min at 2 °C on the formation of biogenic amines (BA). These conditions were applied at the beginning of the ripening (before the 5th day; HHP1) and in the case of ewes' milk cheeses also after 15th days (HHP15). BA formation was greatly influenced by HHP treatments in both types of cheese. HHP1 treatments significantly reduced the amounts of BA after ripening, being tyramine and putrescine the most affected BA in goats' milk cheeses and tyramine and cadaverine in ewes' milk cheeses. The BA reduction in the HHP1 samples could be explained by the significant decrease in microbiological counts, especially in the LAB, enteroccocci and enterobacteria groups at the beginning of ripening. The proteolysis in these samples was also affected reducing the amount of free amino acids. Although proteolysis in ewes' milk cheeses HHP15 was similar than in control samples a reduction of BA was observed probably because the decrease caused on microbial counts.

Biogenic Amine Production by and Phylogenetic Analysis of 23 Photobacterium Species

Photobacterium species are members of the bacterial communities typically associated with scombrotoxin-forming fish. Reclassification and discovery of new Photobacterium species has caused confusion as to which species are capable of biogenic amine production. We analyzed histamine, cadaverine, and putrescine production by 104 Photobacterium strains representing 23 species. The presence of the genes for histidine decarboxylase ( hdc), lysine decarboxylase ( ldc), and ornithine decarboxylase ( odc) was determined by real-time or conventional PCR and whole genome sequencing. Significant histamine production (>200 ppm) was detected in five Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. damselae, and P. phosphoreum. The hdc gene was detected in all of these histamine-producing species except P. phosphoreum. Cadaverine was produced by eight Photobacterium species: P. angustum, P. aquimaris, P. damselae, P. iliopiscarium, P. kishitanii, P. leiognathi, P. mandapamensis, and P. phosphoreum. Putrescine was produced by six Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. leiognathi, P. mandapamensis, and Photobacterium sp. Cadaverine production correlated closely with the presence of the ldc gene, but putrescine production did not correlate closely with the presence of the odc gene. Characterization of the biogenic amine production by Photobacterium species will allow identification of these marine bacteria and help ensure that current guidelines account for mitigation of these bacteria.

Preliminary study on phosphate solubilizing Bacillus subtilis strain Q3 and Paenibacillus sp. strain Q6 for improving cotton growth under alkaline conditions

Background

Low phosphorus availability limits crop production in alkaline calcareous soils in semi-arid regions including Pakistan. Phosphate solubilizing bacteria may improve crop growth on alkaline calcareous soils due to their ability to enhance P availability.

Methods

Twenty rhizobacterial isolates (Q1–Q20) were isolated from rhizosphere of cotton and characterized for their growth promoting attributes in vitro. The selected phosphate solubilizing isolates were further screened for their ability to improve cotton growth under axenic conditions (jar trial). The phosphorus solubilization capacities of selected strains were quantified and these strains were identified through 16S rDNA sequencing.

Results

Isolates Q2, Q3, Q6, Q7, Q8, Q13 and Q14 were able to solubilize phosphate from insoluble sources. Most of these isolates also possessed other traits including catalase activity and ammonia production. The growth promotion assay showed that Q3 was significantly better than most of the other isolates followed by Q6. Maximum root colonization (4.34 × 10⁶ cfu g⁻¹) was observed in case of isolate Q6 followed by Q3. The phosphorus solubilization capacities of these strains were quantified, showing a maximum phosphorus solubilization by Q3 (optical density 2.605 ± 0.06) followed by the Q6 strain. The strain Q3 was identified as Bacillus subtilis (accession # KX788864) and Q6 as Paenibacillus sp. (accession # KX788865) through 16S rDNA sequencing.

Discussion

The bacterial isolates varied in their abilities for different growth promoting traits. The selected PGPR Bacillus subtilis strain Q3 and Paenibacillus sp. strain Q6 have multifarious growth promoting traits including ability to grow at higher EC and pH levels, and phosphorus solubilizing ability. These strains can efficiently colonize cotton roots under salt affected soils and help plants in phosphorus nutrition. It is concluded that both strains are potential candidates for promoting cotton growth under alkaline conditions, however further investigation is required to determine their potential for field application.

The roles of bacteria in the biochemical changes of chill-stored bighead carp (Aristichthys nobilis): Proteins degradation, biogenic amines accumulation, volatiles production, and nucleotides catabolism

This study investigated the biochemical changes (proteins degradation, total volatile basic nitrogen, biogenic amines, volatile organic compounds, nucleotides catabolism and related enzymes) of bighead carp samples inoculated with four different bacteria (Shewanella putrefaciens, Aeromonas sobria, Acinetobacter bohemicus, and Pseudomonas helmanticensis) during storage at 4 ± 1 °C. A. sobria exhibited the strongest proteolytic activity. A. sobria, P. helmanticensis, and S. putrefaciens were responsible for putrescine production, whereas S. putrefaciens was the sole producer of cadaverine. Alcohols and S-compounds were mainly released by A. sobria and S. putrefaciens, respectively. The fastest degradation rates of hypoxanthine riboside and hypoxanthine were found in samples inoculated with P. helmanticensis and S. putrefaciens. Inosine nucleosidase was mainly resulted by A. sobria, P. helmanticensis and S. putrefaciens, whereas xanthine oxidase was derived from both fish muscle and secretions of P. helmanticensis and S. putrefaciens.

Characterization of multifarious plant growth promoting traits of rhizobacterial strain AR6 under Chromium (VI) stress

Plant growth promoting rhizobacteria (PGPR) can increase the host plant tolerance to cope up with heavy metal induced stress, which can be improve plant growth. Thus, the present study was designed to isolate Cr(VI) tolerant PGPR strain and evaluate its plant growth promoting (PGP) properties under Cr(VI) stress. Rhizobacterial strain AR6 was isolated from the rhizosphere of Phaseolus vulgaris L. and showed 99% homology with Cellulosimicrobium funkei (KM032184) in BLASTn analysis. Strain AR6 was specifically selected due to its high Cr(VI) tolerance (1200μg/ml) and substantial production of PGP substances. Strain AR6 produced 36.75μg/ml of indole acetic acid (IAA), 60.40μg/ml of ammonia and 14.23μg/ml of exopolysaccharide (EPS). Moreover, strain AR6 showed positive results for catalase, protease, amylase, lipase production and phosphate solubilization. A trend of Cr(VI) concentration dependent progressive decline for PGP traits of strain AR6 was observed excluding EPS which was regularly increased on increasing concentrations of Cr(VI). Among the four tested Cr(VI) concentrations, 250μg/ml showed the maximum toxicity to PGP activities of strain AR6. Inoculation of rhizobacterial strain AR6 significantly increased the root length of test crops in the presence of Cr(VI) and produced a considerable number of colonizes on the root of versatile dicot and monocot plants. Moreover, strain AR6 exhibited strong antagonistic activity against phytopathogen Aspergillus niger. Thus, the present study suggests that metal tolerant and PGP activities of the rhizobacterial strain AR6 could be exploited for environmental and agricultural issues.

The importance of lactic acid bacteria for the prevention of bacterial growth and their biogenic amines formation: A review

Foodborne pathogens (FBP) represent an important threat to the consumers' health as they are able to cause different foodborne diseases. In order to eliminate the potential risk of those pathogens, lactic acid bacteria (LAB) have received a great attention in the food biotechnology sector since they play an essential function to prevent bacterial growth and reduce the biogenic amines (BAs) formation. The foodborne illnesses (diarrhea, vomiting, and abdominal pain, etc.) caused by those microbial pathogens is due to various reasons, one of them is related to the decarboxylation of available amino acids that lead to BAs production. The formation of BAs by pathogens in foods can cause the deterioration of their nutritional and sensory qualities. BAs formation can also have toxicological impacts and lead to different types of intoxications. The growth of FBP and their BAs production should be monitored and prevented to avoid such problems. LAB is capable of improving food safety by preventing foods spoilage and extending their shelf-life. LAB are utilized by the food industries to produce fermented products with their antibacterial effects as bio-preservative agents to extent their storage period and preserve their nutritive and gustative characteristics. Besides their contribution to the flavor for fermented foods, LAB secretes various antimicrobial substances including organic acids, hydrogen peroxide, and bacteriocins. Consequently, in this paper, the impact of LAB on the growth of FBP and their BAs formation in food has been reviewed extensively.

Growth, biogenic amine production and tyrDC transcription of Enterococcus faecalis in synthetic medium containing defined amino acid concentrations

AIMS

The tyraminogenic potential of the strains Enterococcus faecalis EF37 and ATCC 29212 was investigated in a synthetic medium containing defined amounts of tyrosine and phenylalanine at different temperatures.

METHODS AND RESULTS

Enterococci growth and the production of biogenic amines (BA) were evaluated in relation to their pre-growth in medium containing tyrosine. Significant differences between the two strains were evidenced at metabolic level. Both the pre-adapted strains grew faster in all the tested conditions, independently of the presence of the precursor. Temperatures of 30 and 40°C positively affected the growth parameters. The tyrosine decarboxylase (tyrDC) activity of the strain EF37 was positively affected by pre-adaptation, while ATCC 29212 showed a faster and higher tyramine accumulation with not-adapted cells. The expression analysis of the gene tyrDC confirmed the influence of the growth conditions on gene transcription.

CONCLUSIONS

The small differences found between the two strains in the maximum transcript level reached rapidly after the inoculum and the different behaviour in the tyramine accumulation suggested the possible involvement of complex regulation mechanisms on the tyrDC or on the membrane transport systems, which could affect the different BA accumulation trend.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study gives deeper insight into the metabolic regulation of tyrDC activity of enterococci.

Evaluation of autochthonous micrococcus strains as starter cultures for the production of Kedong sufu

AIMS

The technological properties of 22 micrococcus strains from traditional fermented Kedong sufu were evaluated in order to develop autochthonous starter cultures.

METHODS AND RESULTS

The proteolytic, autolytic and lipolytic activity, salt tolerance, production and degradation of the biogenic amines of six Micrococcus luteus, nine Kocuria kristinae and seven Kocuria rosea were evaluated. The results indicated that these micrococcus strains exhibited a certain technological diversity, and the results also indicated the best properties to be used in mixed starter cultures. Based on the above findings, two sets of autochthonous starters were formulated. Considering the physicochemical properties and sensory characteristics of sufu, the maturation period of sufu was shortened by 30 days. The profiles of free amino acids and peptides partly revealed the mechanism of sensory quality and shorter ripening time of sufu manufactured using autochthonous mixed starters. Compared to back-slopping fermentation, sufu manufactured with selected autochthonous starter cultures exhibited lower levels of total biogenic amines.

CONCLUSIONS

The selected strains could be used as starter to avoid the accumulation of high concentrations of biogenic amines while also maintaining typical sensory characteristics and preserving the autochthonous strains of the traditional Kedong sufu. The maturation times of Kedong sufu were shortened by 30 days with application of the autochthonous starter.

SIGNIFICANCE AND IMPACT OF THE STUDY

Autochthonous mixed starters can reduce the generation of biogenic amines, speed up the sufu maturation process and preserve typical sensory quality. Furthermore, the rotation of two sets of mixed starter cultures can effectively resist phage attack during the production of sufu.

Bacterial ammonia causes significant plant growth inhibition

Many and complex plant-bacteria inter-relationships are found in the rhizosphere, since plants release a variety of photosynthetic exudates from their roots and rhizobacteria produce multifaceted specialized compounds including rich mixtures of volatiles, e.g., the bouquet of Serratia odorifera 4Rx13 is composed of up to 100 volatile organic and inorganic compounds. Here we show that when growing on peptone-rich nutrient medium S. odorifera 4Rx13 and six other rhizobacteria emit high levels of ammonia, which during co-cultivation in compartmented Petri dishes caused alkalization of the neighboring plant medium and subsequently reduced the growth of A. thaliana. It is argued that in nature high-protein resource degradations (carcasses, whey, manure and compost) are also accompanied by bacterial ammonia emission which alters the pH of the rhizosphere and thereby influences organismal diversity and plant-microbe interactions. Consequently, bacterial ammonia emission may be more relevant for plant colonization and growth development than previously thought.

The influences of natural zeolite (cliptinolite) on ammonia and biogenic amine formation by foodborne pathogen

The influence of natural zeolite on biogenic amines (BAs) and ammonia (AMN) production by eight common gram negative and positive foodborne pathogens (FBP) were investigated in histidine decarboxylase broth (HDB). Presence of 1% zeolite in the HDB resulted in significantly higher AMN production. Histamine (HIS) production by gram positive bacteria was as low as 0.5 mg/L, whereas Escherichia coli produced 18.96 mg/L of HIS. The use of zeolite also significantly suppressed HIS accumulation by E. coli, Pseudomonas aeruginosa, S. paratyphi A (P < 0.05), although zeolite addition stimulated HIS production by K. pneumonia and Aeromonas hydrophila. The range of tyramine (TYR) production by gram positive bacteria was 1.19 and 4.06 mg/L for Enteroccus faecalis and Listeria monocytogenes respectively. The results of study showed that the effect of zeolite on BAs and AMN production was dependent on bacterial strains, as well as zeolite concentrations used.

PRACTICAL APPLICATION

Natural zeolites are the main absorptive, low-cost material used in agriculture and industry. Although the effect of zeolite on ammonia formation in some industrial systems is well known, there is limited information regarding the impact of zeolite on biogenic amine (BA) production by foodborne pathogens. The data presented in this article will help us to understand the impact of natural zeolite on BA and ammonia production by eight common foodborne pathogens.

The function of lactic acid bacteria and brine solutions on biogenic amine formation by foodborne pathogens in trout fillets

The influences of lactic acid bacteria and brine solutions on the biogenic amine formation by Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Enterococus faecalis, Pseudomonas aeruginosa, Listeria monocytogenes, Aeromonas hydrophila and Salmonella paratyphi A in fermented trout fillets were investigated. Fish fillets were divided into four groups, group 1 without any lactic acid bacteria inoculation, group 2 and group 3 with different salt concentration inoculated with lactic acid bacteria and food-borne pathogens, and group 4 inoculated with lactic acid bacteria and food-borne pathogens without a salt solution. The histamine content in trout fillets in group 4 was found to be more than 10mg/100g, while the other groups contained less than 7.5mg/100g. The highest tyramine production was found for group 1 and group 3, ranging from 3 to 18mg/100g. Lactic acid bacteria did not seem to play an important role on biogenic amine production by food borne pathogens, while adding brine solution on fillets has inhibitory effects on some of the biogenic amines.

A new method for the determination of biogenic amines in cheese by LC with evaporative light scattering detector

This paper presents a new LC method with evaporative light scattering detection (ELSD), for the separation and determination of the biogenic amines (histamine, spermidine, spermine, tyramine, putrescine and β-phenylethylamine) which are commonly present in cheese, as their presence and relative amounts give useful information about freshness, level of maturing, quality of storage and cheese authentication. The LC-ELSD method is validated by comparison of the results with those obtained through LC-UV determination, based on a pre-column dansyl chloride derivatisation step. The obtained data demonstrate that both methods can be interchangeably used for biogenic amines determination in cheese. The new LC-ELSD method shows good precision and permits to achieve, for standard solutions, limit of detection (LOD) values ranging from 1.4 to 3.6 mg L(-1) and limit of quantitation (LOQ) values ranging from 3.6 to 9.3 mg L(-1). The whole methodology, comprehensive of the homogenization-extraction process and LC-ELSD analysis, has been applied in the analysis of a typical Calabria (Southern Italy) POD cheese, known as Caciocavallo Silano. The most aboundant amine found was histamine, followed, in decreasing order, by tyramine, spermine, putrescine, β-phenylethylamine and spermidine, for a total amount of 127 mg kg(-1). This value does not represent a possible risk for consumer health, according to the toxicity levels reported in literature and regarded as acceptable.