Novel mechanism by which extracellular vesicles derived from Lactobacillus murinus alleviates deoxynivalenol-induced intestinal barrier disruption

Deoxynivalenol (DON) is a common environmental pollutant that poses a serious health risk to humans worldwide. This study was aim to explore whether gut microbiota is involved in DON-induced intestinal toxicity as well as to reveal effect of probiotics derived from gut microbiota in protecting intestinal barrier and to elucidate mechanism. We found that DON caused disturbed gut microbiota, particularly Lactobacillus murinus (L. murinus) deficiency. DON enhanced M1 macrophage polarization and decreased tight junction protein expression. Microbiota transplantation experiments showed that transfer of DON-disrupted microbiota to healthy mice resulted in delivery of DON-induced intestinal toxicity. Besides, DON lost its damaging effect on macrophage and intestinal barrier in antibiotic-treated mice. Further intervention experiments revealed that L. murinus induce macrophage conversion from M1 to M2 phenotype through secreted extracellular vesicles (EVs) to alleviate DON-induced intestinal barrier disruption. Mechanistically, EVs activate TLR2 to promote M2 macrophage polarization and release IL-10, which in turn enhances intestinal barrier function. Upon successful translation of its efficacy into clinical practice, EVs created from L. murinus could be a novel possible treatment strategy for DON-induced gut disease.

Polyguluronate alleviates ulcerative colitis by targeting the gut commensal Lactobacillus murinus and its anti-inflammatory metabolites

Polyguluronate (PG) is a fermentable polysaccharide from edible algae. The present study was designed to investigate the therapeutic effect of PG on ulcerative colitis (UC) and its underlying mechanisms. Our results suggest that oral intake of PG attenuates UC and improves gut microbiota dysbiosis by promoting the growth of Lactobacillus spp. in dextran sulfate sodium-fed mice. Five different species of Lactobacillus were isolated from the feces of PG-treated mice and L. murinus was identified to have the best anti-colitis effect, suggesting a critical role for L. murinus in mediating the therapeutic effect of PG. Furthermore, PG was degraded potentially by the beta-glucuronidase from L. murinus and adding PG to the culture medium of L. murinus remarkably increased its production of anti-inflammatory metabolites, including itaconic acid, cis-11,14-eicosadienoic acid, and 3-amino-3-(2-chlorophenyl)-propionic acid. Additionally, L. salivarius, a human intestine-derived PG-utilizing species that is closely related to L. murinus, was also demonstrated to have potent anti-colitis effects, suggesting that it is a candidate target of PG in the human gut. Altogether, our study illustrates an unprecedented application of PG in the treatment of UC and establishes the basis for understanding its therapeutic effect from the perspective of L. murinus and its metabolites.

Altered Respiratory Microbiomes, Plasma Metabolites, and Immune Responses in Influenza A Virus and Methicillin-Resistant Staphylococcus aureus Coinfection

Influenza A virus (IAV)-methicillin-resistant Staphylococcus aureus (MRSA) coinfection causes severe respiratory infections. The host microbiome plays an important role in respiratory tract infections. However, the relationships among the immune responses, metabolic characteristics, and respiratory microbial characteristics of IAV-MRSA coinfection have not been fully studied. We used specific-pathogen-free (SPF) C57BL/6N mice infected with IAV and MRSA to build a nonlethal model of IAV-MRSA coinfection and characterized the upper respiratory tract (URT) and lower respiratory tract (LRT) microbiomes at 4 and 13 days postinfection by full-length 16S rRNA gene sequencing. Immune response and plasma metabolism profile analyses were performed at 4 days postinfection by flow cytometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The relationships among the LRT microbiota, the immune response, and the plasma metabolism profile were analyzed by Spearman's correlation analysis. IAV-MRSA coinfection showed significant weight loss and lung injury and significantly increased loads of IAV and MRSA in bronchoalveolar lavage fluid (BALF). Microbiome data showed that coinfection significantly increased the relative abundances of Enterococcus faecalis, Enterobacter hormaechei, Citrobacter freundii, and Klebsiella pneumoniae and decreased the relative abundances of Lactobacillus reuteri and Lactobacillus murinus. The percentages of CD4+/CD8+ T cells and B cells in the spleen; the levels of interleukin-9 (IL-9), interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), IL-6, and IL-8 in the lung; and the level of mevalonolactone in plasma were increased in IAV-MRSA-coinfected mice. L. murinus was positively correlated with lung macrophages and natural killer (NK) cells, negatively correlated with spleen B cells and CD4+/CD8+ T cells, and correlated with multiple plasma metabolites. Future research is needed to clarify whether L. murinus mediates or alters the severity of IAV-MRSA coinfection. IMPORTANCE The respiratory microbiome plays an important role in respiratory tract infections. In this study, we characterized the URT and LRT microbiota, the host immune response, and plasma metabolic profiles during IAV-MRSA coinfection and evaluated their correlations. We observed that IAV-MRSA coinfection induced severe lung injury and dysregulated host immunity and plasma metabolic profiles, as evidenced by the aggravation of lung pathological damage, the reduction of innate immune cells, the strong adaptation of the immune response, and the upregulation of mevalonolactone in plasma. L. murinus was strongly correlated with immune cells and plasma metabolites. Our findings contribute to a better understanding of the role of the host microbiome in respiratory tract infections and identified a key bacterial species, L. murinus, that may provide important references for the development of probiotic therapies.

Lactobacillus murinus: A key factor in suppression of enterogenous Candida albicans infections in Compound Agrimony enteritis capsules-treated mice

ETHNOPHARMACOLOGICAL RELEVANCE

Compound Agrimony (FuFangXianHeCao, FFXHC) Enteritis Capsules is an ethnomedicine that is derived from Yi Nationality Herbal Medicine for enteritis treatment. We found that FFXHC reduced the mortality outcomes in enterogenic Candida albicans infected mice models and increased the abundance of Lactobacillus murinus in the intestines. Lactobacillus murinus exhibited comparable therapeutic effects to those of FFXHC in enterogenic Candida albicans infected mice. This study provides novel perspectives into the pharmacological mechanisms of FFXHC.

AIM OF THE STUDY

We investigated the mechanisms via which FFXHC inhibits C. albicans infections and its effects on L. murinus.

MATERIALS AND METHODS

Enterogenous C. albicans infection mice models were established and various parameters, including survival rate, weight change, number of colonies, treatment effects on intestinal mucosa, microecology, and immune cytokines evaluated. Susceptibility of C. albicans to L. murinus was evaluated in vitro.

RESULTS

Treatment with FFXHC reduced the number of colonies, improved the health status, enhanced the survival rates, increased the abundance of L. murinus, reduced damage to the intestinal mucosa, and elevated occludin as well as claudin-1 levels. Interestingly, TNF-α, IFN-γ, IL-10, IL-22, and IL-17A levels were increased while IL-1β levels were suppressed in the intestinal mucosa without any change in peripheral blood cytokine levels. Moreover, FFXHC promoted L. murinus proliferation. This study also confirmed the incubation-dependent anti-C. albicans effects exerted by the metabolic supernatants of L. murinus.

CONCLUSIONS

FFXHC effectively alleviated intestinal infections of C. albicans in mice and increased the abundance of L. murinus. Supplementation of L. murinus in food can achieve the effects that are comparable to those of FFXHC. Thus, L. murinus maybe essential in FFXHC-based treatment of intestinal C. albicans infections.

Combined Inhibition of the TGF-β1/Smad Pathway by Prevotella copri and Lactobacillus murinus to Reduce Inflammation and Fibrosis in Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic disease characterized by inflammation and fibrosis of the bile ducts. Cholestasis may lead to hepatic inflammation and fibrosis, and amelioration of cholestasis may allow recovery from inflammatory and fibrotic pathological damage. Prevotella copri (P. copri) interventions have been reported to significantly improve cholestasis and liver fibrosis in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-induced PSC mouse models. Even though P. copri treatment alone cannot bring about recovery from DDC-induced inflammation, it increases the abundance of Lactobacillus murinus (L. murinus) compared with DDC treatment, which has been reported to have anti-inflammatory effects. The abundance of L. murinus still not recovering to a normal level may underlie hepatic inflammation in P. copri + DDC mice. Separate or combined interventions of P. copri and L. murinus were used to investigate the molecular mechanism underlying the improvement in PSC inflammation and fibrosis. P. copri and L. murinus significantly reduced the hepatic inflammatory cell aggregation and inflammatory factor expression as well as the hepatic collagen content and fibrin factor expression in the PSC mice. Further analysis of phosphorylation and dephosphorylation levels revealed that treating the PSC mice with the P. copri and L. murinus combined intervention inhibited the activity of the DDC-activated TGF-β1/Smad pathway, thereby reducing liver inflammation and fibrosis. The combination of P. copri and L. murinus inhibits the TGF-β1/Smad pathway and reduces inflammation and fibrosis in PSC.

Heat-killed Lactobacillus murinus confers neuroprotection against dopamine neuronal loss by targeting NLRP3 inflammasome

The intestinal flora has become very active in studies related to Parkinson's disease (PD) in recent years. The microbe-gut-brain axis is closely related to the maintenance of brain homeostasis as well as PD pathogenesis. Alterations in gut bacteria can contribute to neuroinflammation and dopamine (DA) neurodegeneration. Lactobacillus murinus, a gram-positive bacterium, is a commensal gut bacteria present in the mammalian gut and considered as a potential probiotic due to its beneficial effects, including anti-inflammatory and antibacterial actions. In this study, the effects of live L. murinus and heat-killed L. murinus on DA neuronal damage in rats and the underlying mechanisms were investigated. Data showed that heat-killed L. murinus ameliorated 6-hydroxydopamine-induced motor dysfunctions and loss of substantia nigra DA neurons, while no protection was shown in live L. murinus treatment. At the same time, heat-killed L. murinus reduced the activation of NLRP3 inflammasome in microglia and the secretion of pro-inflammatory factors, thus inhibiting the development of neuroinflammation. Furthermore, heat-killed L. murinus failed to display its original neuroprotective properties in NLRP3 inflammasome knockout mice. Together, heat-killed L. murinus conferred neuroprotection against DA neuronal loss via the inhibition of microglial NLRP3 inflammasome activation. These findings provide a promising potential for future applications of L. murinus, and also beneficial strategy for PD treatment.

Lactobacillus murinus alleviate intestinal ischemia/reperfusion injury through promoting the release of interleukin-10 from M2 macrophages via Toll-like receptor 2 signaling

BACKGROUND

Intestinal ischemia/reperfusion (I/R) injury has high morbidity and mortality rates. Gut microbiota is a potential key factor affecting intestinal I/R injury. Populations exhibit different sensitivities to intestinal I/R injury; however, whether this interpopulation difference is related to variation in gut microbiota is unclear. Here, to elucidate the interaction between the gut microbiome and intestinal I/R injury, we performed 16S DNA sequencing on the preoperative feces of C57BL/6 mice and fecal microbiota transplantation (FMT) experiments in germ-free mice. The transwell co-culture system of small intestinal organoids extracted from control mice and macrophages extracted from control mice or Toll-like receptor 2 (TLR2)-deficient mice or interleukin-10 (IL-10)-deficient mice were established separately to explore the potential mechanism of reducing intestinal I/R injury.

RESULTS

Intestinal I/R-sensitive (Sen) and intestinal I/R-resistant (Res) mice were first defined according to different survival outcomes of mice suffering from intestinal I/R. Fecal microbiota composition and diversity prior to intestinal ischemia differed between Sen and Res mice. The relative abundance of Lactobacillus murinus (L. murinus) at the species level was drastically higher in Res than that in Sen mice. Clinically, the abundance of L. murinus in preoperative feces of patients undergoing cardiopulmonary bypass surgery was closely related to the degree of intestinal I/R injury after surgery. Treatment with L. murinus significantly prevented intestinal I/R-induced intestinal injury and improved mouse survival, which depended on macrophages involvement. Further, in vitro experiments indicated that promoting the release of IL-10 from macrophages through TLR2 may be a potential mechanism for L. murinus to reduce intestinal I/R injury.

CONCLUSION

The gut microbiome is involved in the postoperative outcome of intestinal I/R. Lactobacillus murinus alleviates mice intestinal I/R injury through macrophages, and promoting the release of IL-10 from macrophages through TLR2 may be a potential mechanism for L. murinus to reduce intestinal I/R injury. This study revealed a novel mechanism of intestinal I/R injury and a new therapeutic strategy for clinical practice. Video Abstract.

The Selective Advantage of the lac Operon for Escherichia coli Is Conditional on Diet and Microbiota Composition

The lac operon is one of the best known gene regulatory circuits and constitutes a landmark example of how bacteria tune their metabolism to nutritional conditions. It is nearly ubiquitous in Escherichia coli strains justifying the use of its phenotype, the ability to consume lactose, for species identification. Lactose is the primary sugar found in milk, which is abundant in mammals during the first weeks of life. However, lactose is virtually non-existent after the weaning period, with humans being an exception as many consume dairy products throughout their lives. The absence of lactose during adulthood in most mammals and the rarity of lactose in the environment, means that the selective pressure for maintaining the lac operon could be weak for long periods of time. Despite the ability to metabolize lactose being a hallmark of E. coli's success when colonizing its primary habitat, the mammalian intestine, the selective value of this trait remains unknown in this ecosystem during adulthood. Here we determine the competitive advantage conferred by the lac operon to a commensal strain of E. coli when colonizing the mouse gut. We find that its benefit, which can be as high as 11%, is contingent on the presence of lactose in the diet and on the presence of other microbiota members in the gut, but the operon is never deleterious. These results help explaining the pervasiveness of the lac operon in E. coli, but also its polymorphism, as lac-negative E. coli strains albeit rare can naturally occur in the gut.

The effect of calorie intake, fasting, and dietary composition on metabolic health and gut microbiota in mice

Background

Calorie restriction (CR) and intermittent fasting (IF) can promote metabolic health through a process that is partially mediated by gut microbiota modulation. To compare the effects of CR and IF with different dietary structures on metabolic health and the gut microbiota, we performed an experiment in which mice were subjected to a CR or IF regimen and an additional IF control (IF^Ctrl) group whose total energy intake was not different from that of the CR group was included. Each regimen was included for normal chow and high-fat diet.

Results

We showed that in normal-chow mice, the IF^Ctrl regimen had similar positive effects on glucose and lipid metabolism as the CR regimen, but the IF regimen showed almost no influence compared to the outcomes observed in the ad libitum group. IF also resulted in improvements, but the effects were less marked than those associate with CR and IF^Ctrl when the mice were fed a high-fat diet. Moreover, CR created a stable and unique gut microbial community, while the gut microbiota shaped by IF exhibited dynamic changes in fasting-refeeding cycles. At the end of each cycle, the gut microbiota of the IF^Ctrl mice was similar to that of the CR mice, and the gut microbiota of the IF mice was similar to that of the ad libitum group. When the abundance of Lactobacillus murinus OTU2 was high, the corresponding metabolic phenotype was improved regardless of eating pattern and dietary structure, which might be one of the key bacterial groups in the gut microbiota that is positively correlated with metabolic amelioration.

Conclusion

There are interactions among the amount of food intake, the diet structure, and the fasting time on metabolic health. The structure and composition of gut microbiota modified by dietary regimens might contribute to the beneficial effects on the host metabolism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-00987-5.

Detection and isolation of the typical gut indigenous bacteria from ddY mice fed a casein-beef tallow-based or egg yolk-based diet

The effects of whole egg on the cecal microbiome of ddY mice has been reported. To investigate the existence of susceptible indigenous bacteria (SIB) to egg yolks (EY), mice were fed a diet containing either 20% (w/w) milk casein and 17% beef tallow (CT) or 12% milk casein and 27% EY for 14 days, and then, the cecal microbiome was analyzed by 16S rRNA (V4) amplicon sequencing. To isolate the typical species in each diet group, culture-dependent viable bacterial counts were determined on Blood Liver (BL) and Gifu Anaerobic Medium (GAM) agar plates. The amplicon sequencing analysis revealed typical CT-SIB, such as Lachnospiraceae-like bacteria, and EY-SIB, such as Allobaculum-, Lactobacillus murinus-, and Bacteroides vulgatus-like bacteria. Two of the detected SIB species, L. murinus- and B. vulgatus-like bacteria, were successfully isolated from the BL and GAM agar plates and defined using a 16S rDNA BLAST search. PRACTICAL APPLICATIONS: The SIB defined in the CT and EY groups might have some effects on the nutritional and functional chemical compounds in the milk casein, beef tallow, and/or EY. Analysis of its functional properties of the isolates might develop the new and unique probiotic strains.

Lactobacillus murinus Improved the Bioavailability of Orally Administered Glycyrrhizic Acid in Rats

Intestinal microbiota has been extensively studied in the context of host health benefit, and it has recently become clear that the gut microbiota influences drug pharmacokinetics and correspondingly efficacy. Intestinal microbiota dysbiosis is closely related with liver cirrhosis, especially the depletion of Lactobacillus. Therefore, the bioavailability of orally administered glycyrrhizic acid (GL) was speculated to be influenced under a pathological state. In the present study, L. murinus was isolated and screened for GL bioconversion capacity in vitro. Compared with Lactobacillus rhamnosus and Lactobacillus acidophilus, L. murinus was chosen for further investigation because it has the highest biotransformation rate. Our results showed that L. murinus could significantly improve the translocation of GL on Caco-2 cell models. Meanwhile, L. murinus was observed to have the ability to bind with the surface of Caco-2 cells and prominently downregulate the transporter gene expression level of multidrug resistance gene 1 (MDR1) and multidrug resistance protein 2 (MRP2), which were involved in the efflux of drugs. Furthermore, L. murinus was selected to be orally administred into rats in healthy and liver cirrhosis groups by a daily gavage protocol. Our data highlighted that supplements of L. murinus significantly improved the bioavailability of orally administered GL in rats, especially under a pathological condition, which may provide a novel strategy for improving the clinical therapeutic effect of liver protective drugs.

Intestinal Dysbiosis and Biotin Deprivation Induce Alopecia through Overgrowth of Lactobacillus murinus in Mice

Metabolism by the gut microbiota affects host physiology beyond the gastrointestinal tract. Here, we find that antibiotic-induced dysbiosis, in particular, overgrowth of Lactobacillus murinus (L. murinus), impaired gut metabolic function and led to the development of alopecia. While deprivation of dietary biotin per se did not affect skin physiology, its simultaneous treatment with vancomycin resulted in hair loss in specific pathogen-free (SPF) mice. Vancomycin treatment induced the accumulation of L. murinus in the gut, which consumes residual biotin and depletes available biotin in the gut. Consistently, L. murinus induced alopecia when monocolonized in germ-free mice fed a biotin-deficient diet. Supplementation of biotin can reverse established alopecia symptoms in the SPF condition, indicating that L. murinus plays a central role in the induction of hair loss via a biotin-dependent manner. Collectively, our results indicate that luminal metabolic alterations associated with gut dysbiosis and dietary modifications can compromise skin physiology.

Predominant gut Lactobacillus murinus strain mediates anti-inflammaging effects in calorie-restricted mice

BACKGROUND

Calorie restriction (CR), which has a potent anti-inflammaging effect, has been demonstrated to induce dramatic changes in the gut microbiota. Whether the modulated gut microbiota contributes to the attenuation of inflammation during CR is unknown, as are the members of the microbial community that may be key mediators of this process.

RESULTS

Here, we report that a unique Lactobacillus-predominated microbial community was rapidly attained in mice within 2 weeks of CR, which decreased the levels of circulating microbial antigens and systemic inflammatory markers such as tumour necrosis factor alpha (TNF-α). Lactobacillus murinus CR147, an isolate in the most abundant operational taxonomic unit (OTU) enriched by CR, downregulated interleukin-8 production in TNF-α-stimulated Caco-2 cells and significantly increased the lifespan and the brood size of the nematode Caenorhabditis elegans. In gnotobiotic mice colonized with the gut microbiota from old mice, this strain decreased their intestinal permeability and serum endotoxin load, consequently attenuating the inflammation induced by the old microbiota.

CONCLUSIONS

Our study demonstrated that a strain of Lactobacillus murinus was promoted in CR mice and causatively contributed to the attenuation of ageing-associated inflammation.

Production, purification and characterization of bacteriocin from Lactobacillus murinus AU06 and its broad antibacterial spectrum

OBJECTIVE

To study the production, purification and characterization of bacteriocin from Lactobacillus murinus AU06 isolated from marine sediments and its broad spectrum of inhibition against fish pathogens.

METHODS

The selected strain was used in production, purification and characterized of bacteriocin. In addition, purified bacteriocin was tested for its antimicrobial activity against fish pathogens.

RESULTS

In the present study, the bacteriocin production was found to be higher at 35 °C, pH 6.0 and was purified to 4.74 fold with 55. 38 U/mg of specific activity with the yield of 28.92%. The molecular weight of the purified bacteriocin was estimated as 21 kDa. The purified bacteriocin exhibited complete inactivation of antimicrobial activity when treated with proteinase K, pronase, chymotrypsin, trypsin, pepsin and papain. The purified bacteriocin exhibited broad inhibitory spectrum against both Gram positive and negative bacteria.

CONCLUSIONS

It is concluded that the ability of bacteriocin in inhibiting a wide-range of pathogenic bacteria is of potential interest for food safety and may have future applications in food preservative.