Gut Glucosinolate Metabolism and Isothiocyanate Production

The glucosinolate‐myrosinase system in plants has been well studied over the years while relatively little research has been undertaken on the bacterial metabolism of glucosinolates. The products of myrosinase based glucosinolate hydrolysis in the human gut are important to health particularly the isothiocyanates as they are shown to have anticancer properties as well as other beneficial roles in human health. This review is concerned with the bacterial metabolism of glucosinolates but is not restricted to the human gut. Isothiocyanate production and nitrile formation are discussed together with the mechanisms of the formation of these compounds. Side chain modification of the methylsulfinylalkyl glucosinolates is reviewed and the implications for bioactivity of the resultant products is also discussed

Processing and Structure of the Lantibiotic Peptide Nso From the Human Gut Bacterium Blautia obeum A2-162 analysed by Mass Spectrometry

A previously reported gene cluster encoding four nisin-like peptides, three with the same sequence (NsoA1-3) and the unique NsoA4, produced antimicrobial activity in the presence of trypsin after heterologous expression in Lactococcus lactis. Protein extracts were separated by SDS gel electrophoresis or immunoprecipitation using an antibody to the NsoA2 leader. Tryptic peptides observed by LC-MS/MS covered the complete sequence of preNsoA1-3 and part of the leader sequence of preNsoA4 and confirmed the expression and the predicted sequences of the preNsoA peptides. Further, the data revealed that the preNsoA1-3 peptides were partly modified with dehydrations and formation of lanthionine rings. A certain amount of fully modified preNsoA1-3 was observed. Details of modifications of the core peptide and the C-terminal tryptic peptide TATCGCHITGK covering rings D and E indicated that 22% of these preNsoA1-3 peptides were completely modified. A lower amount of ring formation is estimated for rings A-C. Intact masses of immunoprecipitation-derived peptides determined by LC-MS accurately matched the expected preNsoA precursor peptides. The most abundant peptides detected were preNsoA2-3-8H2O followed by preNsoA1-8H2O and other states of dehydration. The results confirm incomplete processing of preNsoA peptides in the heterologous system, with the formation of a certain amount of fully modified peptides

Identification of genes required for glucan exopolysaccharide production in Lactobacillus johnsonii suggests a novel mechanism of biosynthesis

Lactobacillus johnsonii FI9785 makes two capsular exopolysaccharides-a heteropolysaccharide (EPS2) encoded by the eps operon and a branched glucan homopolysaccharide (EPS1). The homopolysaccharide is synthesized in the absence of sucrose, and there are no typical glucansucrase genes in the genome. Quantitative proteomics was used to compare the wild type to a mutant where EPS production was reduced to attempt to identify proteins associated with EPS1 biosynthesis. A putative bactoprenol glycosyltransferase, FI9785_242 (242), was less abundant in the Δ eps_cluster mutant strain than in the wild type. Nuclear magnetic resonance (NMR) analysis of isolated EPS showed that deletion of the FI9785_242 gene ( 242) prevented the accumulation of EPS1, without affecting EPS2 synthesis, while plasmid complementation restored EPS1 production. The deletion of 242 also produced a slow-growth phenotype, which could be rescued by complementation. 242 shows amino acid homology to bactoprenol glycosyltransferase GtrB, involved in O-antigen glycosylation, while in silico analysis of the neighboring gene 241 suggested that it encodes a putative flippase with homology to the GtrA superfamily. Deletion of 241 also prevented production of EPS1 and again caused a slow-growth phenotype, while plasmid complementation reinstated EPS1 synthesis. Both genes are highly conserved in L. johnsonii strains isolated from different environments. These results suggest that there may be a novel mechanism for homopolysaccharide synthesis in the Gram-positive L. johnsonii IMPORTANCE Exopolysaccharides are key components of the surfaces of their bacterial producers, contributing to protection, microbial and host interactions, and even virulence. They also have significant applications in industry, and understanding their biosynthetic mechanisms may allow improved production of novel and valuable polymers. Four categories of bacterial exopolysaccharide biosynthesis have been described in detail, but novel enzymes and glycosylation mechanisms are still being described. Our findings that a putative bactoprenol glycosyltransferase and flippase are essential to homopolysaccharide biosynthesis in Lactobacillus johnsonii FI9785 indicate that there may be an alternative mechanism of glucan biosynthesis to the glucansucrase pathway. Disturbance of this synthesis leads to a slow-growth phenotype. Further elucidation of this biosynthesis may give insight into exopolysaccharide production and its impact on the bacterial cell

Expression and delivery of an endolysin to combat Clostridium perfringens

Clostridium perfringens is a cause for increasing concern due to its responsibility for severe infections both in humans and animals, especially poultry. To find new control strategies to treat C. perfringens infection, we investigated the activity and delivery of a bacteriophage endolysin. We identified a new endolysin, designated CP25L, which shows similarity to an N-acetylmuramoyl-l-alanine amidase domain and is distinct from other C. perfringens endolysins whose activity has been demonstrated in vitro. The cp25l gene was cloned and expressed in Escherichia coli, and the gene product demonstrated lytic activity against all 25 C. perfringens strains tested. The probiotic strain Lactobacillus johnsonii FI9785 was engineered to deliver the endolysin to the gastrointestinal tract. The integration of the nisRK two-component regulatory system from the Lactococcus lactis nisin A biosynthesis operon into the chromosome of L. johnsonii allowed constitutive expression of the endolysin under the control of the nisA promoter (P(nisA)), while the use of a signal peptide (SLPmod) led to successful secretion of the active endolysin to the surrounding media. The high specificity and activity of the endolysin suggest that it may be developed as an effective tool to enhance the control of C. perfringens by L. johnsonii in the gastrointestinal tract

Structural analysis of the α-D-glucan produced by the sourdough isolate Lactobacillus brevis E25

Cereal-associated Lactic Acid Bacteria (LAB) are well known for homopolymeric exopolysaccharide (EPS) production. Herein, the structure of an EPS isolated from sourdough isolate Lactobacillus brevis E25 was determined. A modified BHI medium was used for production of EPS-E25 in order to eliminate potential contaminants. Analysis of sugar monomers in EPS revealed that glucose was the only sugar present. Structural characterisation of EPS by NMR and methylation analysis revealed that E25 produced a highly branched α-glucan with (α1→ 3) and (α1→6) glycosidic linkages, and was similar in structure to a previously reported EPS from Lactobacillus reuteri 180. The 1H and 13C NMR data were contrasted with newly recorded data for known polysaccharides (alternan, commercial dextran) which also contain α-(1,3,6)Glc branch points. It was found in both E25 EPS and alternan that NMR parameters could be used to distinguish glucose residues that had the same substitution pattern but occupied different positions in the structure

A decrease in iron availability to human gut microbiome reduces the growth of potentially pathogenic gut bacteria: an in vitro colonic fermentation study

Iron-supplements are widely consumed; however most of the iron is not absorbed and enters the colon where potentially pathogenic bacteria can utilise it for growth. This study investigated the effect of iron availability on human gut microbial composition and function using an in vitro colonic fermentation model inoculated with faecal microbiota from healthy adult donors, as well as examining the effect of iron on the growth of individual gut bacteria. Batch fermenters were seeded with fresh faecal material and supplemented with the iron chelator, bathophenanthroline disulphonic acid (BPDS). Samples were analysed at regular intervals to assess impact on the gut bacterial communities. The growth of Escherichia coli and Salmonella Typhimurium was significantly impaired when cultured independently in iron-deficient media. In contrast, depletion of iron did not affect the growth of the beneficial species, Lactobacillus rhamnosus, when cultured independently. Analysis of the microbiome composition via 16S-based metataxonomics indicated that under conditions of iron chelation, the relative abundance decreased for several taxa, including a 10% decrease in Escherichia and a 15% decrease in Bifidobacterium. Metabolomics analysis using 1 HNMR indicated that the production of SCFAs was reduced under iron-limited conditions. These results support previous studies demonstrating the essentiality of iron for microbial growth and metabolism, but, in addition, they indicate that iron chelation changes the gut microbiota profile and influences human gut microbial homeostasis through both compositional and functional changes

In vitro drug release from acetylated high amylose starch-zein films for oral colon-specific drug delivery

This study describes the preparation of free films of zein with and without acetylated high amylose maize starch (HAS) and their corresponding coated tablets as a novel approach to colonic drug delivery. We hypothesise that the embedding of a digestible starch component within the inert zein would allow the film to remain intact until the large intestine is reached. Free films of zein alone and starch/zein were prepared and characterized. SEM and AFM images of film surface showed that films were morphologically inhomogeneous, particularly at lower HAS/Zein ratios; however, nanothermal analysis data suggested that these differences in appearance within the same film are not compositional differences. Moreover, FT-IR could detect no molecular interaction between the two polymers. Paracetamol tablets were coated with HAS/Zein aqueous based coatings of different compositions to a TWG of 20%. Drug release from zein alone and 1:5 HAS/Zein coated tablets under upper gastrointestinal conditions (pH 1.2, pH 6.8 with pepsin and pancreatin included) was very similar (for example approximately 12% and 14% of the drug was released, respectively, after 6 h in a sequential in vitro test), suggesting that release in this region is limited and is not influenced by the presence of HAS in the ratio to zein under study. Studies using an in vitro colon model showed that under simulated colonic conditions, the drug release was significantly (p < 0.05) more rapid from 1:5 HAS/Zein, compared to the zein alone coating formulation. These data therefore support the potential use of zein-starch mixed films for colonic targeting purposes

Complete Genome Sequence of Ochrobactrum haematophilum FI11154, Isolated from Kunu-Zaki, a Nigerian Millet-Based Fermented Food

Ochrobactrum haematophilum FI11154 was isolated from kunu-zaki, a Nigerian traditional fermented millet-based food. Here, we present the first complete genome sequence of this species. The genome consists of five replicons and contains genes related to iron uptake and phosphatase activities

The divergent restoration effects of Lactobacillus strains in antibiotic-induced dysbiosis

To evaluate functions of Lactobacillus strains, isolated from fermented food, in restoration of ampicillin-induced disruption based on mucosal barrier, gut microbial community and metabolome analyses, three Lactobacillus strains, L. plantarum CGMCC12436 (LacP), L. casei CGMCC 12,435 (LacC) and L. rhamnosus strain GG (LacG) were individually administered to ampicillin-pretreated mice. All three strains significantly restored concentrations of endotoxin and diamine oxidase to control levels. Linear discriminate analysis based on 16S rRNA sequencing of faecal bacteria revealed that the restoration of microbial communities by Lactobacillus strains was more effective than natural restoration. Correlation analysis between microbiota and metabolites indicated that, the higher level of acetate in LacC group was positively correlated with increased relative abundance of Citrobacter, Bifidobacterium and S24-7. Furthermore, LacC down-regulated the expression of NF-κB p65 and modulated the ampicillin-induced inflammatory responses. The LacC strain could particularly attenuate ampicillin-induced disruption by optimisation of microbial taxa and enhancement of acetate and butyrate production

Cytotoxic effects of Saccharomyces cerevisiae TC6 and Lactobacillus brevis TBRC 3003 isolated from Thai fermented foods

Purpose: To determine the cytotoxic effect, anti-colony formation effect and antimigratory effect of Saccharomyces cerevisiae TC6 isolated from Thai water kefir, and Lactobacillus brevis TBRC 3003 isolated from picked cabbage. Methods: Crude microbial extracts were obtained from whole cultures (cells and broths) using ethyl acetate as extracting solvent, and the dried extracts were redissolved in ethanol before use. Cytotoxic, antiproliferative and antimigratory effects of the two microbial extracts on MCF-7, HepG2, and HeLa were tested using 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetra zolium bromide (MTT), clonogenic formation and wound healing assays. Results: Lb. brevis TBRC 3003 showed the highest cytotoxicity toward HepG2 cells (IC50 of 669.72 µg/mL), while S. cerevisiae TC6 showed the highest cytotoxicity against MCF-7 (IC50 of 691.49 µg/mL) and HeLa (IC50 of 379.16 µg/mL) based on MTT assay. Anti-colony formation test showed that S. cerevisiae TC6 was most the most effective in inhibiting colony formation of HepG2 (IC50 of 311.12 µg/mL) and HeLa (IC50 of 494.64 µg/mL), while Lb. brevis TBRC 3003 was the most potent in inhibiting colony formation of MCF-7 (IC50 of 267.88 µg/mL). Conclusion: Both microbes can potentially be implemented in functional foods as bio-therapeutics with chemopreventive properties against breast, liver and cervical cancers