AUG 02, 2016 11:38 AM PDT

Competition Among gut Bacteria Reduces Pathogens

WRITTEN BY: Carmen Leitch
Commensal bacteria, the normal flora in the digestive tract, have a multitude of functions and are critical to health. One of those functions is keeping harmful or pathogenic bacteria out of our guts. Enterotoxigenic Bacteroides fragilis (ETBF) is one such bacterium.
The probiotic potential of colonization is demonstrated with non?toxigenic Bacteroides fragilis (NBTF), protecting the host from enterotoxigenic B. fragilis?induced (EBTF) disease through intraspecific competition via type VI secretion. / Credit: EMBO Reports Hecht et al
A new study has used “specific-pathogen free” (SFP) mice to investigate the gut microbiome.  While these are not truly germ-free, sterile mice, they get tested so they can be confirmed to be free of a specific list of pathogens. Those ‘pathogens’ can be disease-causing microbes, or they can just be commensal organisms.

The paper, published in EMBO Reports, shows that an effector can exclude the ETBF bacterial strain from the gut. Interestingly, a non-toxigenic B. fragilis (NTBF) strain secretes that effector, which thus indicates how strain-specific competition may work to mold the composition of gut microflora communities.
The gut microbiome of humans carries B. fragilis populations that are known to be primarily made up of either ETBF (toxic) or NTBF (non-toxic) strains. That’s a feature that indicated to the researchers that competition could be taking place and may aid in the study of the mechanism of pathogen exclusion.
The type VI secretion system (T6SS), explained in the video above, is a one step mechanism by which bacteria inject effector proteins and virulence factors like proteins or enzymes, from the bacterial cell and directly into a target cell.

It’s been previously demonstrated that T6SSs in B. fragilis manage competition between strains. The researchers compared exclusion of ETBF in strains of NTBF that were normal, or T6SS-deficient (the gene coding for an essential T6SS component tssC was deleted), or T6SS-complemented (tssC was removed from the genome but expressed on a plasmid).

By co-colonizing SPF mice, it was observed that normal NTBF and T6SS-complemented NTBF displayed strain dominance over ETBF.  That dominance was abolished, however, in mice that were co-colonized with NTBF that was T6SS-deficient. It was confirmed that the phenotype of T6SS deficiency was caused by a failure to exclude toxic ETBF, and not from a loss NTBF, after monocolonization by NTBF was not different between normal and T6SS-deficient strains.

The scientists also wanted to see if disease burden was reduced after EPTF was excluded, so they assayed for the toxin it produces. They determined that interstrain competition allowed normal NTBF to provide total protection from ETBF-induced colitis, while T6SS-deficient NTBF only gave partial protection.

Using mass spectrometry to identify the effector, the T6SS secretome was characterized and Bte2 (B. fragilis T6S effector 2) was identified as the most abundant effector. In addition, analysis of an NTBF strain a deficient in Bte2 confirmed that it’s an effector that mediates exclusion of ETBF, and by consequence, lessens the disease burden in the mouse gut.

Consideration of all the data shows that Bte2 secretion by NTBF T6SS shapes the composition of the microbiome and reduces disease burden by targeting EBTF.

Sources: Nature, EMBO Reports
 
About the Author
  • Experienced research scientist and technical expert with authorships on over 30 peer-reviewed publications, traveler to over 70 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
JUL 13, 2021
Microbiology
Expanding Viral Populations May be More Adaptable Than We Knew
JUL 13, 2021
Expanding Viral Populations May be More Adaptable Than We Knew
In nature, growing populations from bacterial colonies to humans tend to expand. In pulled expansions, the individuals a ...
JUL 20, 2021
Cell & Molecular Biology
Do Phages Drive Bacterial Evolution?
JUL 20, 2021
Do Phages Drive Bacterial Evolution?
Antibiotics are a standard treatment for bacterial infections, but more and more of these bacterial infections can't be ...
AUG 10, 2021
Microbiology
Herbal Medicine May Help Restore the Microbiome, Treat Gulf War Illnesses
AUG 10, 2021
Herbal Medicine May Help Restore the Microbiome, Treat Gulf War Illnesses
About one-third of Gulf war veterans have chronic and unexplained medical issues that include gastrointestinal disorders ...
AUG 23, 2021
Microbiology
During a Chronic Viral Infection, Immune Cells May Suffer 'Exhaustion'
AUG 23, 2021
During a Chronic Viral Infection, Immune Cells May Suffer 'Exhaustion'
Several viruses are known to cause chronic infections, one is hepatitis C virus (HCV). Researchers studying these infect ...
AUG 24, 2021
Microbiology
Sugars in Breast Milk May Help Prevent Infections in Newborns
AUG 24, 2021
Sugars in Breast Milk May Help Prevent Infections in Newborns
Research has indicated that babies get many benefits from breastmilk, even if they are only fed that way for a very shor ...
AUG 26, 2021
Coronavirus
Researchers View COVID-19 Progression in a Live Animal Model
AUG 26, 2021
Researchers View COVID-19 Progression in a Live Animal Model
Scientists have used a mouse model to visualize the progression of a SARS-CoV-2 infection as it led to sometimes fatal c ...
Loading Comments...