Mitigation of Desulfovibrio ferrophilus IS5 degradation of X80 carbon steel mechanical properties using a green biocide.

Most microbiologically influenced corrosion (MIC) studies focus on the threat of pinhole leaks caused by MIC pitting. However, microbes can also lead to structural failures. Tetrakis hydroxymethyl phosphonium sulfate (THPS) biocide mitigated the microbial degradation of mechanical properties of X80 steel pipeline by Desulfovibrio ferrophilus (IS5 strain), a very corrosive sulfate reducing bacterium. It was found that 100 ppm (w/w) THPS added to the enriched artificial seawater (EASW) culture medium before incubation resulted in 2.8-log reduction in sessile cell count after a 7-d incubation at 28 °C under anaerobic conditions, leading to 94% uniform corrosion rate reduction (from 1.3 to 0.07 mm/a), and 84% pitting corrosion rate reduction (from 0.70 to 0.11 mm/a). The X80 dogbone coupon incubated with 100 ppm THPS for 7 d suffered 3% loss in ultimate tensile strain and 0% loss in ultimate tensile strength compared with the abiotic control in EASW. In comparison, the no-treatment X80 dogbone coupon suffered losses of 13% in ultimate tensile strain and 6% in ultimate tensile stress, demonstrating very good THPS efficacy.

Transcriptomics and Functional Analysis of Copper Stress Response in the Sulfate-Reducing Bacterium Desulfovibrio alaskensis G20.

Copper (Cu) is an essential micronutrient required as a co-factor in the catalytic center of many enzymes. However, excess Cu can generate pleiotropic effects in the microbial cell. In addition, leaching of Cu from pipelines results in elevated Cu concentration in the environment, which is of public health concern. Sulfate-reducing bacteria (SRB) have been demonstrated to grow in toxic levels of Cu. However, reports on Cu toxicity towards SRB have primarily focused on the degree of toxicity and subsequent elimination. Here, Cu(II) stress-related effects on a model SRB, Desulfovibrio alaskensis G20, is reported. Cu(II) stress effects were assessed as alterations in the transcriptome through RNA-Seq at varying Cu(II) concentrations (5 µM and 15 µM). In the pairwise comparison of control vs. 5 µM Cu(II), 61.43% of genes were downregulated, and 38.57% were upregulated. In control vs. 15 µM Cu(II), 49.51% of genes were downregulated, and 50.5% were upregulated. The results indicated that the expression of inorganic ion transporters and translation machinery was massively modulated. Moreover, changes in the expression of critical biological processes such as DNA transcription and signal transduction were observed at high Cu(II) concentrations. These results will help us better understand the Cu(II) stress-response mechanism and provide avenues for future research.

A tale of two unusual anaerobic bacterial infections in an immunocompetent man: A case report and literature review.

We report a case of an immunocompetent man who presented with Desulfovibrio fairfieldensis bacteremia, followed by an epidural abscess due to Parvimonas micra. Only few cases have described unique clinical features related to both organisms, and this report illustrates two distinct sequential, if not concurrent, syndromes due to these anaerobes.

Exogenous autoinducer-2 inhibits biofilm development of Desulfovibrio sp. Huiquan2017.

Sulfate-reducing bacteria (SRB) are culprits for microbiologically influenced corrosion, and biofilms are believed to play essential roles in the corrosion induced by SRB. However, little is known about the regulation of SRB biofilms. Quorum sensing signal molecules acyl-homoserine lactones (AHLs) and autoinducer-2 (AI-2) regulate biofilm formation of many bacteria. In this study, the production of AHLs and AI-2 by one SRB strain, Desulfovibrio sp. Huiquan2017, was detected, and the effect of exogenous AI-2 on bacterial biofilm formation was discussed. It was found that the cell-free supernatants of Desulfovibrio sp. Huiquan2017 induced luminescence in a ∆luxS mutant strain Vibrio harveyi BB170, indicating the production of functional AI-2 by the bacterium. In the presence of exogenous AI-2, the growth of Desulfovibrio sp. Huiquan2017 and early biofilm formation were not affected, but the later stage of biofilm development was inhibited significantly. The biofilms became looser, smaller, and thinner, and contained less bacteria and extracellular polymeric substances (EPS). The inhibition effect of AI-2 on the biofilm development of Desulfovibrio sp. Huiquan2017 was mainly achieved through reducing the amount of EPS in biofilms. These findings shed light on the biofilm regulation of SRB.

Effect of Durio zibethinus rind polysaccharide on functional constipation and intestinal microbiota in rats.

The prevalence of constipation increases rapidly with the increased pressure of some people's life, which seriously affects the quality of life in related patients. In this study, the improvement of functional constipation by Durio zibethinus Murr rind polysaccharide (DZMP) and the effects of DZMP on intestinal microbiota were investigated in a constipation model of Sprague-Dawley (SD) rats established by loperamide hydrochloride. Results showed that DZMP at 200 mg/kg could significantly (P < 0.05) increase the intestinal transit rate, motilin, gastrin, substance P levels and concentration of short-chain fatty acids (SCFAs), reduce the somatostatin levels and improve the gastrointestinal peristalsis of rats. Sequencing showed that the Lachnospiraceae-NK4A136-group in the rats given 200 mg/kg DZMP (16.07%) was significantly higher than that of the model group (10.13%), while the Desulfovibrio was lower (2.99%) than that of the model group (4.19%). Principal co-ordinates analysis (PcoA) revealed a significant difference in intestinal microbiota composition between the model group and the high-dose DZMP group (200 mg/kg). The results demonstrated that DZMP has a regulatory effect of treating functional constipation and regulating intestinal flora in rats.

Psychrotolerant Antarctic bacteria biosynthesize gold nanoparticles active against sulphate reducing bacteria.

This study evaluates the biosynthesis of gold nanoparticle (GNP) using Antarctic bacteria and assesses its potential antibacterial activity on sulfate-reducing bacteria (SRB). The GNPs were biosynthesized at distinct temperatures (4°, 10°, 25°, 30° and 37° C) using bacterial isolate GL1.3, obtained from Antarctic lake water. Biochemical and phylogenetic analysis concluded that the isolate GL1.3 belongs to Bacillus sp. The GNP biosynthesis was achieved at all the incubation temperatures (4°, 10°, 25°, 30° and 37° C) only during the log phase of growth. These formed nanoparticles were identified by UV-Visible spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to be of size 30-50 nm. These GNPs exhibited antibacterial activity against SRB (Desulfovibrio sp.) evaluated by broth micro-dilution method. At 200 µg mL-1 GNP concentrations, being the minimal inhibitory concentration (MIC), the growth rate and sulfate reducing activity of Desulfovibrio sp. were reduced by 12% and 7% respectively. Comet assay revealed that the genotoxic effect of GNP on SRB is responsible for the inhibition of its growth and sulfide production. This showed that the Antarctic microbes could be useful for GNP synthesis even under psychrophilic conditions for various biomedical applications.

Health risk of Licorice-Yuanhua combination through induction of colonic H2S metabolism.

ETHNOPHARMACOLOGICAL RELEVANCE: Licorice and Yuanhua are both famous herbs in Traditional Chinese Medicine (TCM), and their combination is used by some TCM doctors to treat renal and gastrointestinal diseases as well as tumors. On the other hand, the compatibility theory of TCM warns that toxic effects might be triggered by Licorice-Yuanhua combination. The usability of Licorice-Yuanhua combination has long been controversial due to lack of evidence and mechanism illustration. Colonic hydrogen sulfide (H2S) metabolism imbalance is closely related with colonic inflammation, tumor promotion and many other diseases. AIM OF THE STUDY: This study was carried out to investigate if licorice-Yuanhua combination could induce potential toxic effects in the aspect of colonic H2S metabolism. MATERIALS AND METHODS: Normal mice were treated with high or low doses of Licorice, Yuanhua and Licorice-Yuanhua combination. Fecal H2S concentration was measured by colorimetric method, colon sulfomucin production was compared through tissue staining, fecal microbiota and microbial metagenomes were analyzed by 16S rDNA sequencing and data mining. RESULTS: Data shows that although licorice cannot change colonic H2S concentration, it can exacerbate Yuanhua induced H2S rising. Licorice or Yuanhua increases colon sulfomucin production, and their combination further enhances this effect. 16S rDNA sequencing analysis revealed that licorice or Yuanhua has little influence on gut microbiota, however, licorice-Yuanhua combination can impact gut microbiota structural balance and increase the abundance of Desulfovibrio genus and other related genera. Moreover, the combination extensively changes microbial metagenomes, influencing 1172 genes that cannot be changed by individual licorice or Yuanhua. By searching in KEGG database, ten genes are annotated with H2S producing gene, and these genes are remarkably increased by licorice-Yuanhua combination, more significantly than licorice or Yuanhua. CONCLUSIONS: This study provides evidences and mechanisms for licorice induced risks, which is related with colonic H2S metabolism disturbance, gut microbiota and microbial metagenomes. More risk assessment should be evaluated when licorice was used in combination with foods, herbs or drugs. The study provides an example where healthy risks can be induced by combination of food additive, herbs or drugs, through regulating gut microbiota and its metagenomes.

Adaptation of Desulfovibrio alaskensis G20 to perchlorate, a specific inhibitor of sulfate reduction.

Hydrogen sulfide produced by sulfate-reducing microorganisms (SRM) poses significant health and economic risks, particularly during oil recovery. Previous studies identified perchlorate as a specific inhibitor of SRM. However, constant inhibitor addition to natural systems results in new selective pressures. Consequently, we investigated the ability of Desulfovibrio alaskensis G20 to evolve perchlorate resistance. Serial transfers in increasing concentrations of perchlorate led to robust growth in the presence of 100 mM inhibitor. Isolated adapted strains demonstrated a threefold increase in perchlorate resistance compared to the wild-type ancestor. Whole genome sequencing revealed a single base substitution in Dde_2265, the sulfate adenylyltransferase (sat). We purified and biochemically characterized the Sat from both wild-type and adapted strains, and showed that the adapted Sat was approximately threefold more resistant to perchlorate inhibition, mirroring whole cell results. The ability of this mutation to confer resistance across other inhibitors of sulfidogenesis was also assayed. The generalizability of this mutation was confirmed in multiple evolving G20 cultures and in another SRM, D. vulgaris Hildenborough. This work demonstrates that a single nucleotide polymorphism in Sat can have a significant impact on developing perchlorate resistance and emphasizes the value of adaptive laboratory evolution for understanding microbial responses to environmental perturbations.

Effect of selected biocides on microbiologically influenced corrosion caused by Desulfovibrio ferrophilus IS5.

The marine bacterial strain Desulfovibrio ferrophilus IS5, known for its lithotrophic growth ability to use metallic iron as a sole electron donor and for causing corrosion of steel, was used in the current study. Four commonly used biocides in the oil and gas industry, namely tetrakis(hydroxymethyl) phosphonium sulfate (THPS), glutaraldehyde (GLUT), benzalkonium chloride (BAC), and GLUT/BAC were selected to study their efficacy in controlling carbon steel corrosion in the presence of this strain. Incubations containing strain IS5 and low carbon steel coupons were prepared in the presence and absence of the four biocides, and these were monitored using both electrochemical methods (electrochemical impedance spectroscopy, linear polarization resistance and potentiodynamic polarization) and surface analyses (scanning electron microscopy, confocal measurements, optical microscopy, and profilometry) to assess the biofilm/metal interactions. When THPS, BAC, and GLUT/BAC treatments were applied, minimal corrosion was measured by all methods. In contrast, severe pitting was observed in the presence of 50 ppm GLUT, similar to what was observed when D. ferrophilus IS5 was incubated in the absence of biocide, suggesting that GLUT alone may not be effective in controlling MIC in marine environments. This study also showed that the use of non-destructive electrochemical methods is effective for screening for real time biocide selection and monitoring of the impact of chemicals post-dosage in oil and gas operations.

Hexagonal Boron Nitride: The Thinnest Insulating Barrier to Microbial Corrosion.

We report the use of a single layer of two-dimensional hexagonal boron nitride (SL-hBN) as the thinnest insulating barrier to microbial corrosion induced by the sulfate-reducing bacteria Desulfovibrio alaskensis G20. We used electrochemical methods to assess the corrosion resistance of SL-hBN on copper against the effects of both the planktonic and sessile forms of the sulfate-reducing bacteria. Cyclic voltammetry results show that SL-hBN-Cu is effective in suppressing corrosion effects of the planktonic cells at potentials as high as 0.2 V ( vs Ag/AgCl). The peak anodic current for the SL-hBN coatings is ∼36 times lower than that of bare Cu. Linear polarization resistance tests confirm that the SL-hBN coatings serve as a barrier against corrosive effects of the G20 biofilm when compared to bare Cu. The SL-hBN serves as an impermeable barrier to aggressive metabolites and offers ∼91% corrosion inhibition efficiency, which is comparable to much thicker commercial coatings such as polyaniline. In addition to impermeability, the insulating nature of SL-hBN suppresses galvanic effects and improves its ability to combat microbial corrosion.

Multi-heme cytochromes provide a pathway for survival in energy-limited environments.

Bacterial reduction of oxidized sulfur species (OSS) is critical for energy production in anaerobic marine subsurfaces. In organic-poor sediments, H2 has been considered as a major energy source for bacterial respiration. We identified outer-membrane cytochromes (OMCs) that are broadly conserved in sediment OSS-respiring bacteria and enable cells to directly use electrons from insoluble minerals via extracellular electron transport. Biochemical, transcriptomic, and microscopic analyses revealed that the identified OMCs were highly expressed on the surface of cells and nanofilaments in response to electron donor limitation. This electron uptake mechanism provides sufficient but minimum energy to drive the reduction of sulfate and other OSS. These results suggest a widespread mechanism for survival of OSS-respiring bacteria via electron uptake from solid minerals in energy-poor marine sediments.

Hydrogen Sulfide and Sulfate Prebiotic Stimulates the Secretion of GLP-1 and Improves Glycemia in Male Mice.

Recently, the gastrointestinal microbiome, and its metabolites, has emerged as a potential regulator of host metabolism. However, to date little is known on the precise mechanisms of how this regulation occurs. Hydrogen sulfide (H2S) is abundantly produced in the colon by sulfate-reducing bacteria (SRB). H2S is a bioactive gas that plays regulatory roles in many systems, including metabolic hormone regulation. This gas metabolite is produced in close proximity to the glucagonlike peptide-1 (GLP-1)-secreting cells in the gut epithelium. GLP-1 is a peptide hormone that plays pivotal roles in both glucose homeostasis and appetite regulation. We hypothesized that H2S can directly regulate GLP-1 secretion. We demonstrated that H2S donors (NaHS and GYY4137) directly stimulate GLP-1 secretion in murine L-cells (GLUTag) and that this occurs through p38 mitogen-activated protein kinase without affecting cell viability. We then increased SRB in mice by supplementing the diet with a prebiotic chondroitin sulfate for 4 weeks. Mice treated with chondroitin sulfate had elevated Desulfovibrio piger levels in the feces and increased colonic and fecal H2S concentration. These animals also had enhanced GLP-1 and insulin secretion, improved oral glucose tolerance, and reduced food consumption. These results indicate that H2S plays a stimulatory role in GLP-1 secretion and that sulfate prebiotics can enhance GLP-1 release and its downstream metabolic actions.

Black Raspberries and Their Anthocyanin and Fiber Fractions Alter the Composition and Diversity of Gut Microbiota in F-344 Rats.

Natural compounds can alter the diversity and composition of the gut microbiome, potentially benefiting our health. We previously demonstrated chemopreventive effects of black raspberries (BRBs) in colorectal cancer, which is associated with gut dysbiosis. To investigate the effects of whole BRBs and their fractions on gut microbiota, we fed F-344 rats a control diet, 5% BRBs, the BRB anthocyanin fraction, or the BRB residue fraction for 6 weeks. Feces were collected at baseline and at weeks 3 and 6, and bacterial sequence counts were analyzed. We observed distinct patterns of microbiota from different diet groups. Beta diversity analysis suggested that all diet groups exerted time-dependent changes in the bacterial diversity. Hierarchical clustering analysis revealed that post-diet fecal microbiota was segregated from baseline fecal microbiota within each diet. It is interesting to note that fractions of BRBs induced different changes in gut bacteria compared to whole BRBs. The abundance of specific microbial species known to have anti-inflammatory effects, such as Akkermansia and Desulfovibrio, was increased by whole BRBs and their residue. Further, butyrate-producing bacteria, e.g., Anaerostipes, were increased by whole BRBs. Our results suggest that whole BRBs and their fractions alter the gut microbiota in ways that could significantly influence human health.

Fish oil, lard and soybean oil differentially shape gut microbiota of middle-aged rats.

High-fat diets have been associated with overweight/obesity and increased mortality in middle-aged populations. However, it is still unclear how gut microbiota in middle-aged populations responds to dietary fats at a normal dose. In this study, we explored gut microbiota structure in middle-aged rats (aged 12 months) after feeding 4% (w/w) soybean oil, lard or fish oil for 3 months, respectively. The results showed that the gut microbiota structure in the fish oil group was substantially different from those of the soybean oil and lard groups in both in vitro and in vivo studies. The relative abundances of phylum Proteobacteria and genus Desulfovibrio in the caecal and colonic contents were the highest in the fish oil group (p < 0.05). The mRNA levels of biomarkers for inflammation in the colon, including IL-1ß, IL-6, IL-17, IL-18 and TNF-α, were also the highest in the fish oil group (p < 0.05). Meanwhile, the fish oil group had the highest microbial DNA abundance of a predicted lipid metabolism. Our results gave a new insight into the potentially negative impact of fish oil diet on health of middle-aged populations by changing gut microbiota and inducing inflammation as compared to soybean oil and lard diets.

System-Wide Adaptations of Desulfovibrio alaskensis G20 to Phosphate-Limited Conditions.

The prevalence of lipids devoid of phosphorus suggests that the availability of phosphorus limits microbial growth and activity in many anoxic, stratified environments. To better understand the response of anaerobic bacteria to phosphate limitation and starvation, this study combines microscopic and lipid analyses with the measurements of fitness of pooled barcoded transposon mutants of the model sulfate reducing bacterium Desulfovibrio alaskensis G20. Phosphate-limited G20 has lower growth rates and replaces more than 90% of its membrane phospholipids by a mixture of monoglycosyl diacylglycerol (MGDG), glycuronic acid diacylglycerol (GADG) and ornithine lipids, lacks polyphosphate granules, and synthesizes other cellular inclusions. Analyses of pooled and individual mutants reveal the importance of the high-affinity phosphate transport system (the Pst system), PhoR, and glycolipid and ornithine lipid synthases during phosphate limitation. The phosphate-dependent synthesis of MGDG in G20 and the widespread occurrence of the MGDG/GADG synthase among sulfate reducing ∂-Proteobacteria implicate these microbes in the production of abundant MGDG in anaerobic environments where the concentrations of phosphate are lower than 10 µM. Numerous predicted changes in the composition of the cell envelope and systems involved in transport, maintenance of cytoplasmic redox potential, central metabolism and regulatory pathways also suggest an impact of phosphate limitation on the susceptibility of sulfate reducing bacteria to other anthropogenic or environmental stresses.

Effects of Ag and Cu ions on the microbial corrosion of 316L stainless steel in the presence of Desulfovibrio sp.

The utilization of Ag and Cu ions to prevent both microbial corrosion and biofilm formation has recently increased. The emphasis of this study lies on the effects of Ag and Cu ions on the microbial corrosion of 316L stainless steel (SS) induced by Desulfovibrio sp. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to analyze the corrosion behavior. The biofilm formation, corrosion products and Ag and Cu ions on the surfaces were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and elemental mapping. Through circuit modeling, EIS results were used to interpret the physicoelectric interactions between the electrode, biofilm and culture interfaces. EIS results indicated that the metabolic activity of Desulfovibrio sp. accelerated the corrosion rate of SS in both conditions with and without ions. However, due to the retardation in the growth of Desulfovibrio sp. in the presence of Ag and Cu ions, significant decrease in corrosion rate was observed in the culture with the ions. In addition, SEM and EIS analyses revealed that the presence of the ions leads to the formation on the SS of a biofilm with different structure and morphology. Elemental analysis with EDS detected mainly sulfide- and phosphorous-based corrosion products on the surfaces.

Bismuth(III) deferiprone effectively inhibits growth of Desulfovibrio desulfuricans ATCC 27774.

Sulfate-reducing bacteria have been implicated in inflammatory bowel diseases and ulcerative colitis in humans and there is an interest in inhibiting the growth of these sulfide-producing bacteria. This research explores the use of several chelators of bismuth to determine the most effective chelator to inhibit the growth of sulfate-reducing bacteria. For our studies, Desulfovibrio desulfuricans ATCC 27774 was grown with nitrate as the electron acceptor and chelated bismuth compounds were added to test for inhibition of growth. Varying levels of inhibition were attributed to bismuth chelated with subsalicylate or citrate but the most effective inhibition of growth by D. desulfuricans was with bismuth chelated by deferiprone, 3-hydroxy-1,2-dimethyl-4(1H)-pyridone. Growth of D. desulfuricans was inhibited by 10 µM bismuth as deferiprone:bismuth with either nitrate or sulfate respiration. Our studies indicate deferiprone:bismuth has bacteriostatic activity on D. desulfuricans because the inhibition can be reversed following exposure to 1 mM bismuth for 1 h at 32 °C. We suggest that deferiprone is an appropriate chelator for bismuth to control growth of sulfate-reducing bacteria because deferiprone is relatively nontoxic to animals, including humans, and has been used for many years to bind Fe(III) in the treatment of ß-thalassemia.

Biocorrosion of Endodontic Files through the Action of Two Species of Sulfate-reducing Bacteria: Desulfovibrio desulfuricans and Desulfovibrio fairfieldensis.

AIM: This study assessed the biocorrosive capacity of two bacteria: Desulfovibrio desulfuricans and Desulfovibrio fairfieldensis on endodontic files, as a preliminary step in the development of a biopharmaceutical, to facilitate the removal of endodontic file fragments from root canals. MATERIALS AND METHODS: In the first stage, the corrosive potential of the artificial saliva medium (ASM), modified Postgate E medium (MPEM), 2.5 % sodium hypochlorite (NaOCl) solution and white medium (WM), without the inoculation of bacteria was assessed by immersion assays. In the second stage, test samples were inoculated with the two species of sulphur-reducing bacteria (SRB) on ASM and modified artificial saliva medium (MASM). In the third stage, test samples were inoculated with the same species on MPEM, ASM and MASM. All test samples were viewed under an infinite focus Alicona microscope. RESULTS: No test sample became corroded when immersed only in media, without bacteria. With the exception of one test sample between those inoculated with bacteria in ASM and MASM, there was no evidence of corrosion. Fifty percent of the test samples demonstrated a greater intensity of biocorrosion when compared with the initial assays. CONCLUSION: Desulfovibrio desulfuricans and D. fairfieldensis are capable of promoting biocorrosion of the steel constituent of endodontic files. CLINICAL SIGNIFICANCE: This study describes the initial development of a biopharmaceutical to facilitate the removal of endodontic file fragments from root canals, which can be successfully implicated in endodontic therapy in order to avoiding parendodontic surgery or even tooth loss in such events.

Glycomacropeptide is a prebiotic that reduces Desulfovibrio bacteria, increases cecal short-chain fatty acids, and is anti-inflammatory in mice.

Glycomacropeptide (GMP) is a 64-amino acid (AA) glycophosphopeptide with application to the nutritional management of phenylketonuria (PKU), obesity, and inflammatory bowel disease (IBD). GMP is a putative prebiotic based on extensive glycosylation with sialic acid, galactose, and galactosamine. Our objective was to determine the prebiotic properties of GMP by characterizing cecal and fecal microbiota populations, short-chain fatty acids (SCFA), and immune responses. Weanling PKU (Pah(enu2)) and wild-type (WT) C57Bl/6 mice were fed isoenergetic AA, GMP, or casein diets for 8 wk. The cecal content and feces were collected for microbial DNA extraction to perform 16S microbiota analysis by Ion Torrent PGM sequencing. SCFA were determined by gas chromatography, plasma cytokines via a Bio-Plex Pro assay, and splenocyte T cell populations by flow cytometry. Changes in cecal and fecal microbiota are primarily diet dependent. The GMP diet resulted in a reduction from 30-35 to 7% in Proteobacteria, genera Desulfovibrio, in both WT and PKU mice with genotype-dependent changes in Bacteroidetes or Firmicutes. Cecal concentrations of the SCFA acetate, propionate, and butyrate were increased with GMP. The percentage of stimulated spleen cells producing interferon-γ (IFN-γ) was significantly reduced in mice fed GMP compared with casein. In summary, plasma concentrations of IFN-γ, TNF-α, IL-1ß, and IL-2 were reduced in mice fed GMP. GMP is a prebiotic based on reduction in Desulfovibrio, increased SCFA, and lower indexes of inflammation compared with casein and AA diets in mice. Functional foods made with GMP may be beneficial in the management of PKU, obesity, and IBD.

Relationships between bacterial energetic metabolism, mercury methylation potential, and hgcA/hgcB gene expression in Desulfovibrio dechloroacetivorans BerOc1.

The proteins encoded by the hgcA and hgcB genes are currently the only ones known to be involved in the mercury methylation by anaerobic microorganisms. However, no studies have been published to determine the relationships between their expression level and the net/gross methylmercury production. This study aimed to decipher the effect of growth conditions on methylmercury production and the relationships between hgcA and hgcB expression levels and net methylation. Desulfovibrio dechloroacetivorans strain BerOc1 was grown under sulfidogenic conditions with different carbon sources and electron donors as well as under fumarate respiration. A good correlation was found between the biomass production and the methylmercury production when the strain was grown under sulfate-reducing conditions. Methylmercury production was much higher under fumarate respiration when no sulfide was produced. During exponential growth, hgcA and hgcB gene expression levels were only slightly higher in the presence of inorganic mercury, and it was difficult to conclude whether there was a significant induction of hgcA and hgcB genes by inorganic mercury. Besides, no relationships between hgcA and hgcB expression levels and net mercury methylation could be observed when the strain was grown either under sulfate reduction or fumarate respiration, indicating that environmental factors had more influence than expression levels.