Biology subjects

Xu, Q.

Publications and source records attributed to Xu, Q..

At least 217 records · Page 12Linked to original sources

bioRxiv2019

Dynamic chromosome rearrangements of the white-spotted bamboo shark shed light on cartilaginous fish diversification mechanisms

Cartilaginous fishes have a very high phenotypical diversity, a phenomenon for which the mechanisms have been largely unexplored. Here, we report the genome of the white-spotted bamboo shark as the first chromosome-level genome assembly of cartilaginous fish. Using this genome, we illustrated a dynamic chromosome rearrangement process in the bamboo shark, which resulted in the formation of 13 chromosomes, all of which were sparsely distributed with conserved genes and fast-evolving. We found the fast-evolving chromosomes to be enriched in immune-related genes with two chromosomes harboring the major genes for developing the single-chain antibody. We also found chromosome rearrangements to have resulted in the loss of two genes (p2rx3 and p2rx5) which we also showed were involved in cartilage development using a CRISPR/Cas9 approach in zebrafish. Our study highlighted the significance of chromosome rearrangements in the phenotypical evolution of cartilaginous fishes, providing clues to inform further studies on mechanisms for fish diversification.

genomics↗

bioRxiv2019

Deep transcriptome sequencing of subgenual anterior cingulate cortex reveals disorder-specific expression changes in major psychiatric disorders

How do differences in onset, symptoms, and treatment response arise between various mental illnesses despite substantial overlap of genetic risk factors? To address this question, we carried out deep RNA sequencing of human postmortem subgenual anterior cingulate cortex, a key component of limbic circuits linked to mental illness. Samples were obtained from 200 individuals diagnosed with bipolar disorder, schizophrenia, or major depression, and controls. Differential expression analysis in cases versus controls detected modest differences that were similar across disorders, although transcript-level differences were more pronounced. Case-case comparisons revealed greater expression differences between disorders, including many genes and transcripts that were expressed in opposite directions in each diagnostic group, compared to controls. Relative transcript abundances were associated with common genetic variants that accounted for disproportionate fractions of diagnosis-specific heritability. Inherited genetic risk factors shape the brain transcriptome and contribute to diagnostic differences between broad classes of mental illness.

genomics↗

bioRxiv2019

Three-dimensional genome reorganization during mouse spermatogenesis

Three-dimensional genome organization plays an important role in many biological processes. Yet, how the genome is packaged at the molecular level during mammalian spermatogenesis remains unclear. Here, we performed Hi-C in seven sequential stages during mouse spermatogenesis. We found that topological associating domains (TADs) and chromatin loops underwent highly dynamic reorganization. They displayed clear existence in primitive type A spermatogonia, disappearance at pachytene stage, and reestablishment in spermatozoa. Surprisingly, even in the absence of TADs and chromatin loops at pachytene stage, CTCF remained bound at TAD boundary regions (identified in primitive type A spermatogonia). Additionally, many enhancers and promoters exhibited features of open chromatin and transcription remained active at pachytene stage. A/B compartmentalization and segmentation ratio were conserved in different stages of spermatogenesis in autosomes, although there were A/B compartment switching events correlated with gene activity changes. Intriguingly, A/B compartment structure on the X chromosome disappeared during pacSC, rST and eST stages. Together, our work uncovered a dynamic three-dimensional chromatin organization during mouse spermatogenesis and suggested that transcriptional regulation could be independent of TADs and chromatin loops at specific developmental stages.

genomics↗

bioRxiv2019

Neuronal histone methyltransferase EZH2 regulates neuronal morphogenesis, synaptic plasticity, and cognitive behavior of mice

Recent studies showed that in the nervous system histone methyltransferase EZH2-mediated trimethylation of histone H3 lysine 27 (H3K27me3) acts to regulate neural stem cell proliferation and fate specificity through silencing different gene sets. Here we explored the function of EZH2 in early post-mitotic excitatory neurons by generating a neuronal specific Ezh2 conditional knockout mouse line. The results showed that lack of neuronal EZH2 led to delayed neuronal migration, more complex dendritic arborization, and significantly increased dendritic spine density. RNA-sequencing (RNA-seq) experiments comparing control and Ezh2 knockout neurons revealed that neuronal EZH2 regulated genes related to neuronal morphogenesis. In particular, Pak3 was identified as a target gene suppressed by EZH2 and H3K27me3, and expression of dominant negative PAK3 reversed Ezh2 knockout-induced higher dendritic spine density. Lastly, lack of neuronal EZH2 resulted in impaired memory behaviors in adult mice. Our results demonstrated that neuronal EZH2 played important roles in controlling multiple steps of neuronal morphogenesis during development, which had long-lasting effects on cognitive function in adult mice.

neuroscience↗

bioRxiv2019

ProtCID: A tool for hypothesis generation of the structures of protein interactions

Structural information on the interactions of proteins with other molecules is plentiful, and for some proteins and protein families, there may be 100s of available structures. It can be very difficult for a scientist who is not trained in structural bioinformatics to access this information comprehensively. Previously, we developed the Protein Common Interface Database (ProtCID), which provided clusters of the interfaces of full-length protein chains as a means of identifying biological assemblies. Because proteins consist of domains that act as modular functional units, we have extended the analysis in ProtCID to the individual domain level. This has greatly increased the number of large protein-protein clusters in ProtCID, enabling the generation of hypotheses on the structures of biological assemblies of many systems. The analysis of domain families allows us to extend ProtCID to the interactions of domains with peptides, nucleic acids, and ligands. ProtCID provides complete annotations and coordinate sets for every cluster.

bioinformatics↗

bioRxiv2019

Principles and characteristics of biological assemblies in experimentally determined protein structures

More than half of all structures in the PDB are assemblies of two or more proteins, including both homooligomers and heterooligomers. Structural information on these assemblies comes from X-ray crystallography, NMR, and cryo-EM spectroscopy. The correct assembly in an X-ray structure is often ambiguous, and computational methods have been developed to identify the most likely biologically relevant assembly based on physical properties of assemblies and sequence conservation in interfaces. Taking advantage of the large number of structures now available, some of the most recent methods have relied on similarity of interfaces and assemblies across structures of homologous proteins.

bioinformatics↗

bioRxiv2019

Translating antibiotic prescribing into antimicrobial resistance in the environment: a hazard characterisation case study

The use and misuse of antibiotics in humans, animals and agriculture since penicillins mass production in 1942 has contributed to the current global crisis of drug-resistant infections. Often overlooked are the unintended consequences of such widespread antibiotic use, such as the chronic environmental release of unmetabolised, bioactive antibiotics and antibiotic-resistance genes found in human and animals waste, particularly during and immediately after antibiotic treatment. Here, we report on the potential impact on antibiotic resistance gene selection in rivers from the antibiotic prescribing practice of the National Health Service (NHS) of England. Macrolide and fluoroquinolone prescription data from 2015/16 were used to model the concentrations of antibiotics in a highly populous, sewage-impacted English catchment. Predicted antibiotic concentrations in the river were compared against predicted no-effect concentrations (PNEC) to assess the hazard of antibiotic resistance selection. The study revealed that PNECs for macrolides and fluoroquinolones were exceeded in 63% and 73% of the length of the modelled River Thames catchment, respectively. Potential reductions in macrolide and fluoroquinolone prescriptions (e.g., 4% and 20%) were not shown to translate into meaningful reductions in the hazard of AMR selection in the river. Reductions in macrolide and fluoroquinolone prescribing of 77% and 85%, respectively, were necessary to alleviate the AMR selection hazard from 90+% of the modelled river catchment. Improved antibiotic stewardship, alone, is unlikely to alleviate the identified challenge. Action is needed to substantially reduce antibiotic prescribing, stimulate and implement innovation in sewage-treatment, reduce non-antibiotic drivers of antibiotic resistance (e.g., biocides, metals), and consider regulating antibiotic-resistance DNA as a pollutant.

microbiology↗

bioRxiv2019

Recent origin of an XX/XY sex-determination system in the ancient plant lineage Ginkgo biloba

Sexual dimorphism like dioecy (separate male and female individuals) have evolved in diverse multicellular eukaryotes while the molecular mechanisms underlying the development of such a key biological trait remains elusive (1). The living fossil Ginkgo biloba represents an early diverged lineage of land plants with dioecy. However, its sex-determination system and molecular basis have long been controversial or unknown. In the present research, we assembled the first and largest to date chromosome-level genome of a non-model tree species using Hi-C data. With this reference genome, we addressed both questions using genome resequencing data gathered from 97 male and 265 female trees of ginkgo, as well as transcriptome data from three developmental stages for both sexes. Our results support vertebrate-like XY chromosomes for ginkgo and five potential sex-determination genes, which may originate ~14 million years ago. This is the earliest diverged sex determination region in all reported plants as yet. The present research resolved a long-term controversy, lay a foundation for future studies on the origin and evolution of plant sexes, and provide genetic markers for sex identification of ginkgo which will be valuable for both nurseries and field ecology of ginkgo.

evolutionary biology↗

bioRxiv2018

Dietary sulfate-driven and gut dysbiosis-triggered breast cancer-related gene upregulation

By gut microbiota metagenomic analysis, we found that the abundance of sulfatase-secreting bacteria (SSB) in the gut of mice fed chondroitin sulfate (CS) increases with significant individual difference. The fluctuation of lipopolysaccharide (LPS) and pro-inflammatory indicators with significant individual and tissue variations was also observed. After mice were fed mixed with CS or injected separately with LPS, the breast cancer-related transcriptional factor genes, BCL11A and RUNX1, were upregulated, whereas the tumor suppressor gene, TP53BP1, were downregulated. Further, the mammary myopithelium marker CK5/6, the mammary hyperplasia marker Ki-67, and other tumor markers were also upregulated. While the exogenous estradiol does not induce the expression of BCL11A, RUNX1, and TP53BP1, the estrogen receptor (ER) agonist Fulvestrant that mimics estradiol action not only elevates estradiol concentrations, but also upregulates tumor marker expression levels, revealing that ER inflammatory inactivation and hyperestrogenemia induction might be the etiological cues of breast cancer origin. This study has preliminarily established a possible correlation of gut microbiota dysbiosis and chronic low-grade inflammation with the early-phase onset of breast cancer in mice. The statistical insignificance of test data was attributed to the individual difference of gut microbiota compositions, which determining the individual and tissue variations of systemic inflammation.

cancer biology↗

bioRxiv2018

Single-cell RNA-seq identifies a reversible epithelial-mesenchymal transition in abnormally specified epithelia of p63 EEC syndrome

Mutations in transcription factor p63 are associated with developmental disorders that manifest defects in stratified epithelia including the epidermis. The underlying cellular and molecular mechanism is however not yet understood. We established an epidermal commitment model using human induced pluripotent stem cells (iPSCs) and characterized differentiation defects of iPSCs derived from ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome patients carrying p63 mutations. Transcriptome analyses revealed distinct step-wise cell fate transitions during epidermal commitment; from multipotent simple epithelium to basal stratified epithelia, and ultimately to the mature epidermal fate. Differentiation defects of EEC iPSCs caused by mutant p63 occurred during the specification switch from the simple epithelium to the basal stratified epithelial fate. Single-cell transcriptome and pseudotime analyses identified signatures of embryonic epithelial-mesenchymal transition (EMT) associated with the deviated commitment route of EEC iPSCs. Repressing mesodermal activation reversed the EMT and enhanced epidermal commitment. Our findings demonstrate that p63 is required for specification of stratified epithelia, probably by repressing embryonic EMT during epidermal commitment. This study provides insights into disease mechanisms underlying stratified epithelial defects caused by p63 mutations and suggests potential therapeutic strategies for the disease.\n\nSignificance statementMutations in p63 cause several developmental disorders with defects of epithelial related organs and tissues including the epidermis. Our study is to dissect the unknown cellular and molecular pathomechanism. We utilized human induced pluripotent stem cells (iPSCs) derived from ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome patients carrying p63 mutations and studied transcriptome changes during differentiation of these cells to epidermal cells. Our analyses showed that the specification of the proper epithelial cell fate was affected by p63 EEC mutations, with an abnormal embryonic epithelial-mesenchymal transition (EMT). Repressing mesodermal activation reversed the EMT and enhanced epidermal commitment. This study provides insights into disease mechanisms associated with p63 mutations and suggests potential therapeutic strategies.

developmental biology↗

bioRxiv2018

Spring mineral water-borne bacteria reshape gut microbiota profiles and confer health benefits

BackgroundAlthough dietary patterns are recognized to affect health by interfering with gut microbiota homeostasis, whether live or dead bacteria-bearing spring mineral water (MW) would also exert beneficial effects on health upon curing gut dysbiosis remains unknown.\n\nResultsDue to harboring live bacteria, the heated but unboiled MW from Bama, where centenarians are ubiquitously inhabited, reshapes the gut microbiota from a traveler-type to a local resident-type except for Prevotella. While chondroitin sulfate, a component occurring in livestock and poultry meats, increases the richness of sulfatase-secreting bacteria and sulfate-reducing bacteria, Bama MW dampens the overgrowth of those colon-thinning bacteria and hampers the overexpression of multiple genes responsible for anti-inflammation, anti-oxidation, anti-hypoxia, anti-mutagenesis, and anti-tumorigenesis.\n\nConclusionsBama spring MW prevents the early-phase onset of breast cancer by curating gut dysbiosis. MW also compromises chromosomal DNA damage and ameliorate mitochondrial dysfunctions, implying it may extend lifespan.

microbiology↗

bioRxiv2018

Reversal of microRNA-blocked tumor suppressors by biphenyl- dicarboxylate impedes endotoxin-induced hepatic hyperplasia

Hepatocellular carcinoma (HCC) is one of the most common malignant tumor and the leading cause of cancer-related death worldwide. Biphenyldicarboxylate (BPDC), an intermediate of schisandrin C from Schisandra chinensis, has been used as a hepatoprotective agent that compromises hepatic injuries in China for decades. Whether BPDC is also implicated in the prevention of HCC remains understood. Here, we report that the bacterial endotoxin lipopolysaccharide (LPS) promotes hepatic inflammation and hyperplasia, during which the common tumor markers, alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA), were unregulated, whereas the tumor suppressors, PTEN, FOXO1 and MEN1, were downregulated through increasing the microRNAs, miR-21, miR-122 and miR-24. In contrast, BPDC dampened hepatic inflammation and hyperplasia accompanied by the upregulation of PTEN, FOXO1 and MEN1 through decreasing miR-21, miR-122 and miR-24. However, BPDC failed to downregulate the tumor marker AEG-1 via increasing miR-195. Taken together, BPDC exerts anti-tumor effects by upregulating tumor suppressors upon decreases of miRNAs rather than downregulating tumor markers by increases of miRNAs.

cancer biology↗

bioRxiv2018

Short-hairpin RNA-guided single gene knockdown reverses triple-negative breast cancer

BackgroundThe origin of breast cancer remains poorly understood. Here, we testify a putative mechanism of \"breast cancer origin from inducible nitric oxide synthase (iNOS) activation and oestrogen receptor alpha (ER) inactivation\", which are classified as the essential outcomes of chronic inflammatory responses.\n\nMethodsTo reverse breast cancer status, iNOS was downregulated by short-hairpin RNA (shRNA)-guided NOS2 knockdown from human triple-negative breast cancer (TNBC) cells. To re-enact breast cancer origin, ER was downregulated by shRNA-directed ESR1 knockdown in human mammary epithelial cells.\n\nResultsUpon NOS2 knockdown from HCC1937 cells, the specific TNBC transcription factor genes, RUNX1 and BCL11A, were downregulated, hypoxia was compromised, Warburg effects were attenuated, and tumourigenic proliferation was halted, accompanied by an increase in the tumour marker cyclin D1 (CD1) and a decrease in the tumour suppressor cyclin-dependent kinase inhibitor (CKI). In contrast, ESR1 knockdown from MCF-10A cells led to upregulated BCL11A and RUNX1 expression, augmented hypoxic responses, pronounced Warburg effects, and enhanced PI3K/Akt/mTOR signalling, together with low levels of CD1 and high levels of CKI induction.\n\nConclusionsBreast cancer should originate from inflammatory signalling, during which iNOS activation and ER inactivation elicit hypoxia, oxidation, mitochondrial dysfunction, and breast cancer-like hyperplasia, demonstrating that iNOS inhibitors and ER activators represent promising candidate prodrugs enabling breast cancer prevention in the early stage.

cancer biology↗

bioRxiv2018

An improved high-quality genome assembly and annotation of Qingke, Tibetan hulless barley

BackgroundThe Tibetan hulless barley (Hordeum vulgare L. var. nudum), also called \"Qingke\" in Chinese and \"Ne\" in Tibetan, is the staple food for Tibetans and an important livestock feed in the Tibetan Plateau. The Tibetan hulless barley in China has about 3500 years of cultivation history, mainly produced in Tibet, Qinghai, Sichuan, Yunnan and other areas. In addition, Tibetan hulless barley has rich nutritional value and outstanding health effects, including the beta glucan, dietary fiber, amylopectin, the contents of trace elements, which are higher than any other cereal crops.\n\nFindingsHere, we reported an improved high-quality assembly of Tibetan hulless barley genome with 4.0 Gb in size. We employed the falcon assembly package, scaffolding and error correction tools to finish improvement using PacBio long reads sequencing technology, with contig and scaffold N50 lengths of 1.563Mb and 4.006Mb, respectively, representing more continuous than the original Tibetan hulless barley genome nearly two orders of magnitude. We also re-annotated the new assembly, and reported 61,303 stringent confident putative protein-coding genes, of which 40,457 is HC genes. We have developed a new Tibetan hulless barley genome database (THBGD) to download and use friendly, as well as to better manage the information of the Tibetan hulless barley genetic resources.\n\nConclusionsThe availability of new Tibetan hulless barley genome and annotations will take the genetics of Tibetan hulless barley to a new level and will greatly simplify the breeders effort. It will also enrich the granary of the Tibetan people.

genomics↗

bioRxiv2018

Application of clinical genomic sequencing among Chinese advanced cancer patients to guide precision medicine decisions

PurposeA number of studies have suggested that high-throughput genomic analyses might improve the outcomes of cancer patients. However, whether integrative information about genomic sequencing and related clinical interpretation may benefit Chinese cancer patients with stage IV disease to date has not investigated.\n\nMethodsTargeted gene panel and whole exome of tumor/blood samples in > 1,000 Chinese cancer patients were sequenced. Then we provided patients and their oncologists with the sequencing results and a clinical recommendation roadmap based on evidence-based medicine, defined as CWES. Only patients with stage IV disease who failed the previous treatment upon receiving the CWES reports were included for analyzing the impact of CWES on clinical outcomes in 1-year follow-ups.\n\nResultsWe identified the mutational signatures of 953 Chinese cancer patients, with some being unique. Approximately 88.6% of patients had clinically actionable somatic genomic alterations. We successfully followed up 22 stage IV patients. Of these, 11 patients treatment followed the CWES reports defined as group A. Eleven patients received the next treatment, but did not follow the CWES suggestions, and are defined as group B. The types of therapies before CWES were similar in the two groups. The median PFS of group A was 12 months and 45% patients failed this round of therapy. The median PFS of group B was 4 months and 91% of patients failed the treatment.\n\nConclusionThe current study suggested that CWES has the potential to help explore the clinical benefits in multiple line therapies among advanced stage tumor patients.

cancer biology↗

bioRxiv2018

Comprehensive analysis of potential immunotherapy genomic biomarkers in 1,000 Chinese patients with cancer

BackgroundTumor mutation burden (TMB), DNA mismatch repair deficiency (dMMR), microsatellite instability (MSI), and PD-L1 amplification (PD-L1 AMP) may predict the efficacy of PD-1/PD-L1 blockade. In this study, we aimed to characterize the distributions of these biomarkers in over 1,000 Chinese patients with cancer.\n\nMethodsTMB, MSI, dMMR, and PD-L1 AMP were determined based on whole-exome sequencing of tumor/blood samples from > 1,000 Chinese patients with cancer.\n\nResultsIncidence rates among 953 Chinese patients with cancer showing high TMB (TMB-H), high MSI (MSI-H), dMMR and PD-L1 AMP were 35%, 4%, 0.53% and 3.79%, respectively. We found higher rates of TMB-H among hepatocellular carcinoma, breast cancer, and esophageal cancer patients than was reported for The Cancer Genome Atlas data. Lung cancer patients with EGFR mutations had significantly lower TMB values than those with wild-type EGFR, and increased TMB was significantly associated with dMMR in colorectal cancer (CRC). The frequency of tumors with MSI-H was highest in CRC (14%) and gastric cancer (4%). PD-L1 AMP occurred most frequently in lung squamous cell carcinoma (14.3%) and HER2-positive breast cancer (8.8%). Most MSI-H and dMMR cases exhibited TMB-H, but the overlap among the other biomarkers was low.\n\nConclusionWhile MSI and dMMR are associated with higher mutational loads, correlations between TMB-H and other biomarkers, between MSI-H and dMMR, and between PD-L1 AMP and other biomarkers were low, indicating different underlying causes of the four biomarkers. Thus, it is recommended that all four biomarkers be assessed for certain cancers before administration of PD-1/PD-L1 blockade treatment.

cancer biology↗

bioRxiv2018

Eradication of ENO1-deleted Glioblastoma through Collateral Lethality

Inhibiting glycolysis remains an aspirational approach for the treatment of cancer. We recently demonstrated that SF2312, a natural product phosphonate antibiotic, is a potent inhibitor of the glycolytic enzyme Enolase with potential utility for the collateral lethality-based treatment of Enolase-deficient glioblastoma (GBM). However, phosphonates are anionic at physiological pH, limiting cell and tissue permeability. Here, we show that addition of pivaloyloxymethyl (POM) groups to SF2312 (POMSF) dramatically increases potency, leading to inhibition of glycolysis and killing of ENO1-deleted glioma cells in the low nM range. But the utility of POMSF in vivo is dose-limited by severe hemolytic anemia. A derivative, POMHEX, shows equipotency to POMSF without inducing hemolytic anemia. POMHEX can eradicate intracranial orthotopic ENO1-deleted tumors, despite sub-optimal pharmacokinetic properties. Taken together, our data provide in vivo proof-of-principal for collateral lethality in precision oncology and showcase POMHEX as a useful molecule for the study of glycolysis in cancer metabolism.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC=\"FIGDIR/small/331538_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (20K):\norg.highwire.dtl.DTLVardef@1b78ebcorg.highwire.dtl.DTLVardef@1fc0ccforg.highwire.dtl.DTLVardef@ad268corg.highwire.dtl.DTLVardef@1bdee32_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2018

The MarR Family Regulator BmrR is involved in Bile Tolerance of Bifidobacterium longum BBMN68 via Controlling the Expression of an ABC-Transporter

In order to colonize the human gastrointestinal tract and exert their beneficial effects, bifidobacteria must effectively cope with the toxic bile salts in the intestine, but the molecular mechanism underlying bile tolerance is poorly understood. In this study, heterologous expression of a MarR family transcriptional regulator BmrR significantly reduced ox-bile resistance of Lactococcus lactis NZ9000, suggesting that it might play a role in bile stress response. In silico analysis combined with RT-PCR assay demonstrated that bmrR was co-transcribed with bmrA and bmrB, which encoded multidrug resistance (MDR) ABC transporters. Promoter prediction and EMSA assay revealed that BmrR could autoregulate the bmrRAB operon by binding to bmr box (ATTGTTG-6nt-CAACAAT) in the promoter region. Moreover, heterologous expression of bmrA and bmrB in L. lactis showed 20.77-fold higher tolerance to 0.10% ox-bile compared to wild type strain. In addition, ox-bile could disrupt the DNA binding activity of BmrR as a ligand. Taken together, our findings indicate that bmrRAB operon is autoregulated by transcriptional regulator BmrR and ox-bile serves as an inducer to activate the bile efflux transporter BmrAB in response to bile stress in B. longum BBMN68.\n\nImportanceBifidobacteria are natural inhabitants of the human intestinal tract. Some bifidobacterial strains are used as probiotics in fermented dairy production because of their health-promoting effects. Following consumption, bifidobacteria finally colonize the lower intestinal tract where the concentration of bile salts remains nearly 0.05% to 2.0%. Bile salts as detergent-like antimicrobial compounds can cause disruption of the cellular membrane, protein misfolding and DNA damage. Therefore, tolerance to physiological bile stress is indeed essential for bifidobacteria to survive and exert the probiotic effects in gastrointestinal tract. In B. longum BBMN68, the MarR-type regulator BmrR was involved in bile stress response by auto-regulating bmrRAB operon and ox-bile as an inducer could increase the expression of BmrAB transporter to enhance the bile tolerance of BBMN68.This is the first report about functional analysis of bmrRAB operon in bile stress response, which will provide new insight into bile tolerance mechanisms in Bifidobacterium and other bacteria.

microbiology↗