Scientist - News - 21-09-2009:

LGG successful thanks to hair-like structures
Beintema, Nienke

The probiotic strain LGG, present in a popular yoghurt drink, is a champion in sticking to our intestinal mucus. An international research team has found a plausible explanation for this essential characteristic.

Genetically, Lactobacillus rhamnosus GG (LGG) hardly differs from its close relative L. rhamnosus LC705. Functionally, however, there is one major difference: LGG has probiotic properties, whereas LC705 does not. A team of Finnish, Belgian and Dutch scientists decided to find out why that is, and found a very promising clue: LGG has tiny hair-like structures on its cell surface that allow it to bind to the human intestinal mucus layer. The team published their results in the Proceedings of the National Academy of Sciences (PNAS, online on Sept. 17).
The scientists, led by Wageningen microbiologist and Spinoza Prize laureate Willem de Vos, compared the full genomes of the two Lactobacillus strains to identify their exact differences. It turned out that LGG had genes coding for so-called pili: nanometer-scale surface structures that resemble tiny hairs. Such pili are common in pathogens, but have never been identified in probiotic Lactobacilli. In pathogens they are believed to contribute to their ability to stick to intestinal mucus, and to communicate with the host’s immune system.

Tempting to speculate
To test whether the pili of LGG also played a role in adherence to mucus, the scientists developed a strain in which the gene SpaC, oding for the tip of the pili, was disabled. Indeed, these bacteria no longer adhered to human mucus. "Our findings represent the previously unreported observation of pili in probiotic lactic acid bacteria," write the authors, "indicating how the probiotic strain GG may persist in the host and possibly compete with pathogens for residence sites in the human intestinal tract."
Also, since the pili from certain pathogens have established immunostimulatory effects, the authors find it "tempting to speculate that the observed pili structures could function as immune stimuli that may support some health-promoting properties of LGG."

More information:
Article in PNAS