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 & Ongoing 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:

  1. Which of the hdc gene products are necessary for the conversion of external histidine to histamine;
  2. Where do the hdc proteins localize;
  3. Which of the hdc gene products are necessary for the repression of host cytokines; and
  4. 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. 

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.

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.

Gnotobiotic Mouse Models of Inflammation Associated Cancer

Probiotics (beneficial microbes) are being used with an increasing frequency as an alternative mode for treating inflammatory bowel disease patients. Intrinsic connection between inflammation and cancer promotion is well established and is especially found in patients with colorectal cancer (CRC). Although probiotics have shown success in ameliorating inflammation associated carcinoma, the mechanisms on how probiotic bacteria or their metabolites interact with the host and possess such beneficial effects is barely understood.

Currently, Dr. Bhanu Priya Ganesh is using a germ-free mouse model of colitis associated cancer to study whether and how Lactobacillus reuteri ATCC PTA 6475 or L. reuteri 4659 can attenuate inflammation-associated carcinogenesis. Germfree/Gnotobiotic mice experiments will help us to understand the molecular interactions of a specific bacterial strain with the host in finer detail. In our study, we focus on investigating the beneficial effects of L. reuteri 6475 or L. reuteri 4659 on host health. By doing so, we can identify the bacterial factors of certain beneficial microbial strains which might enhance the host health during severe inflammation. Understanding these mechanisms will facilitate natural probiotic strains as specific therapies in the future to treat IBD associated cancer patients.

Gut-Brain Interactions of Commensal Microorganisms

Early postnatal microbial colonization overlaps with a critical time in the development of the central nervous system. Recent research has started to address the methods of microbiota-gut-brain communication, but we currently lack mechanistic knowledge regarding the effects of normal bacterial colonization on the development and function of the brain.  Specific knowledge of how these interactions influence development is important to human health because they could have implications on brain function and behavior later in life. As we discover how complex gastrointestinal communities of microorganisms interact with the human host, graduate student Berkley Luk is investigating how particular gut commensals affect the host nervous system via secretion of neuroactive molecules.