The Versalovic Lab's primary focus is to understand how commensal bacteria and commensal-derived probiotics modulate mammalian immunity and intestinal physiology. We explore the biology of probiotic or beneficial bacteria that are derived from the commensal microbiota and the mammalian microbiome. Probiotic Lactobacillus strains suppress pro-inflammatory cytokines and modulate intracellular signaling pathways in macrophages and intestinal epithelial cells. Secreted factors derived from probiotics regulate immune cell signaling and may hold the key to understanding molecular mechanisms of probiosis. Natural and engineered probiotics are being developed to treat patients with inflammatory diseases of the gastrointestinal tract and to prevent gastrointestinal infections in human populations.
Current & On-going Projects
Characterization of the histidine decarboxylase gene cluster in Lactobacillus reuteri
Lactobacillus reuteri, a Gram-positive lactic acid-producing bacterium, is indigenous to the gastrointestinal tract of humans. Lactic acid bacteria generate biogenic amines via metabolic conversions, generating biological signals with compounds such as histamine. Our lab recently demonstrated that histamine secreted by L. reuteri was able to modulate the host immune response by inhibiting a known pro-inflammatory cytokine, tumor necrosis factor alpha (TNF-α).
Histamine synthesis results from the decarboxylation of the amino acid histidine to histamine by histidine decarboxylases, a process which results in the secretion of histamine into the environment through a transporter. Analysis of the sequenced Lactobacillus genomes has revealed that L. reuteri 6475 is one of the few beneficial microbes known to possess the necessary and complete set of genes required to synthesize and transport histamine. The histidine decarboxylase (hdc) gene cluster includes hdcA (a putative histidine decarboxylase), hdcB (a protein with unknown function), hdcP (a putative antiporter) and HisS (a possible regulator of histamine production). Currently, Dr Coreen Johnson is taking this research further to discover:
- Which of the hdc gene products are necessary for the conversion of external histidine to histamine;
- Where do the hdc proteins localize;
- Which of the hdc gene products are necessary for the repression of host cytokines; and
- How is the synthesis of histamine regulated in L reuteri. We believe this work will contribute to a greater understanding of the role of beneficial microbes in the gastrointestinal tract.
Gut-Brain Interactions of commensal microorganisms
As we discover how complex gastrointestinal communities of microorganisms interact with the human host, Dr. Karina Pokusaeva is investigating how particular gut commensals affect the enteric nervous system via secretion of small potentially neuroactive molecules.
Interaction of Lactobacillus reuteri within a commensal bacterial community
The probiotic Lactobacillus reuteri produces both inter- and intra-kingdom signaling molecules. Inter-kingdom signaling between L. reuteri and the host leads to modulation of the host immune response during gastrointestinal (GI) tract colonization, in part by inducing host signaling pathways.Intra-kingdom signaling between L. reuteri and the greater bacterial community modulates the composition of the human microbiota in part though the production of an antimicrobial peptide, however other undefined molecules may also contribute. Moreover, the specific interactions between L. reuteri and other members of the bacterial community have not been characterized. It is hypothesized that the composition of the microbiota is regulated by factors secreted by L. reuteri that modulate the colonization or persistence of commensal organisms. Dr. Kathryn Pflughoeft is studying the interactions of L. reuteri within a defined commensal community characteristic of the murine intestinal population, which consists of bacteria that together have been termed the Altered Schaedler Flora (ASF), using in vitro and in vivo co-culture models. Analyzing L. reuteri in combination with the ASF strains provides the opportunity to identify interactions occurring in a complex community similar to that observed during GI tract colonization. The changes in gene expression of L. reuteri and the ASF strains when the probiotic is introduced into the community are being assess using RNAseq. The interaction of L. reuteri with ASF organisms in an in vitro biofilm model as well as in the mouse intestine are being examined using fluorescence in-situ hybridization (FISH). The overall goal for this project is to gain a more complete understanding of the probiotic properties of L. reuteri.
L. reuteri-mediated immunomodulation
Dr Peera Hemarajata is studying the functions of potential transcriptional factors and transporters that modulate the production of immunomodulatory compounds secreted from L. reuteri, both in the targeted and global approaches. He is using targeted mutagenesis along with high-throughput technologies and bioinformatic analysis to explore the transcriptomes and proteomes of the bacteria, in order to identify the functions of potential target genes. Genetic modification of these genes might lead to novel strains of probiotics that can be safely administered to effectively prevent or even treat gastrointestinal inflammation in the near future.
Mouse Colitis Model
Probiotics are being used with an increasing frequency as an alternative mode for treatment of inflammatory bowel disease under well-defined conditions. But the mechanism on how probiotic bacteria exert the anti-inflammatory effects is barely understood. Currently, Chunxu Gao is using a trinitrobenzene sulfonic acid-induced mouse model of colitis to study whether and how Lactobacillus reuteri ATCC PTA 6475 attenuate colitis and inflammation-associated carcinogenesis in vivo. Understanding these mechanisms will facilitate probiotic engineering or rational selection of natural probiotic strains as specific therapies.
Recently Completed Projects
- Tetrahydrofolate Synthesis gene (THFS)
- Probiotics Derived Histamine
- Effects of probiotics on rotavirus infections