The secret weapons of S. salivarius


Streptococcus salivarius is a bacterium that lives peacefully in our digestive tract. A team of researchers at UCL has highlighted the communication and attack mechanisms that allow it to fight other bacteria with which it competes and that are sometimes harmful to us.

In numerical terms, the human body has ten times more bacteria and fungi than cells! Our digestive tract is home to more than 700 species of bacteria and fungi. Their main functions: to help us digest and to protect ourselves against the proliferation of ‘bad’ bacteria, which, like salmonella or listeria, can make us sick. ‘The intestinal flora is an ecosystem where competition for space and food is intense!’ says Dr Johann Mignolet, a researcher at the Institute of Life Sciences, in Prof. Pascal Hols’s laboratory. ‘In this highly competitive environment, the behaviour of Streptococcus salivarius is particularly interesting.’

A ‘nice’ streptococcus

The family of streptococci has several ‘bad’ species. Streptococcus mutans is responsible for tooth decay, S. pneumoniae causes certain pneumonias, S. pyogenes scarlet fever, etc. ‘S. salivarius, on the other hand, is called a good bacterium,’ Dr Mignolet says. ‘It is used in particular as a probiotic. It is particularly abundant in the oral flora and also in the intestine.’

While it’s beneficial to humans, S. salivarius shows no tenderness toward other species of bacteria! ‘Not only can it kill them with bacteriocins, it can also capture and absorb some of the genetic material (DNA) of its “victims” and change its own genome, when it finds something of value – a new defence mechanism, for example. A bit like a tribe of cannibals who eat the heart or brain of their enemies to appropriate their “powers”!’

Communicate to attack

S. salivarius has a communication system: pheromones (ComS) that allow it to exchange information on the status of its peers and, where appropriate, to coordinate attacks against other species. Indeed, the more S. salivarius in the vicinity, the more ComS. ‘When the presence of ComS reaches a certain level, the S. salivarius community senses it as a stressor and activates a transcription factor, ComR. This regulator triggers at the same time the two mechanisms mentioned above: the release of bacteriocins and the capture of the DNA of the bacteria thus killed. These two mechanisms exist in other species, but the particularity of S. salivarius is that they are triggered simultaneously.’(1)

An ‘antibioticbacterium?

That’s not all! The researchers also found that the antibiotic power of S. salivarius goes beyond its streptococcal ‘cousins’. ‘In general, the bacteriocins of a bacterium are directed against a specific range of targets, often species of the same family,’ Dr Mignolet explains. ‘We’ve found that S. salivarius bacteriocins can kill staphylococcus aureus, listeria and even some enterococci – pathogenic bacteria that resist more and more antibiotic treatments.’

These results need to be confirmed and refined, but they open up interesting prospects for certain multiresistant bacteria. ‘We could administer ComS (the “pheromones”) via food to induce the response of S. salivarius, regardless of the bacterial populations present. Or we could isolate and produce its bacteriocins to fight against other harmful bacteria.’2 And thus add an extra weapon to our antibiotic arsenal.

Candice Leblanc

(1) Mignolet, J. et al., ‘Circuitry rewiring directly couples competence to predation in the gut dweller Streptococcus salivarius’, in Cell Reports, February 2018.  
(2) Prof. Hols’s laboratory is continuing its research in collaboration with the company Syngulon, where Dr Mignolet currently works. This start-up’s speciality is the use of bacteriocins for biotechnological and biomedical purposes.  

A glance at Johann Mignolet's bio

J.Mignolet and Pr Hols

2004              Master’s Degree in Biology, University of Namur
2009              PhD, Molecular Biology, University of Namur
2009-10         Postdoctoral Researcher, ULB (Prof. C. Van Lint)
2010-13         Postdoctoral Researcher, University of Geneva (Prof. P. Viollier)
2013-16         Postdoctoral Researcher, UCL (Prof. P. Hols) 
Since 2017    Researcher, Syngulon

Dr Mignolet’s research is funded mainly by the FNRS, the IUAP-BELSPO and UCL.

Published on March 22, 2018