The discovery of the genes responsible for small appendages in Bifidobacterium may help to explain how the probiotic bacteria colonise the intestine.
The research finding, published in Proceedings of the National Academy of Sciences (PNAS), comes after the team of scientists sequenced the DNA of Bifidobacterium breve UCC2003, showing for the first time that Bifidobacteria have genes which produce finger-like appendages known as TAD pili – which allow them to adhere to the gut lining and form colonies.
The researchers, led by Dr Mary O’Connell-Motherway and Professor Douwe van Sinderen, said that the presence of TAD pili in Bifidobacteria suggests a common mechanism for gut colonisation, adding that their results could have major applications in the functional food and infant formula industries.
“The identification of TAD pili is a significant step towards understanding the interaction between bifidobacteria and their host and how the microbiota influences gastrointestinal health” said Fergus Shanahan, professor and chairman of the department of medicine and director of the Alimentary Pharmabiotic Centre, University College Cork.
Dr. O'Connell Motherway told NutraIngredients that her research team used the Bifidobacterium breve UCC2003 strain as a template genome to identify genes groups (locus) that are similar across the range of Bifidobacterium.
Whilst sequencing the genome of the Bifidobacterium breve strain, they noticed that it contained a locus that could potentially produce TAD pili. The group then checked for the presence of the gene cluster in other strains of Bifidobacterium, and found that it is found the genome of every Bifidobacteria strain that has been sequenced.
“We went on to demonstrate the pili are only expressed when the bifidobacteria are in a host. They are not expressed when you grow the cultures in a test tube under lab conditions,” explained O'Connell Motherway.
From this finding the researchers were able to determine that there is a signal received by the Bifidobacterium when in a host, which turn on the pili, however O'Connell Motherway said that the team “don’t know, as yet, what that signal is.”
She said that by knocking out the gene for the TAD pili, the team were also able to create a mutant strain, which was no longer able to colonise the gut.
“These pili are essential for colonisation of Bifidobacterium when they are in the gastrointestinal tract …Other Bifidobacterium have this gene cluster, so it’s a common mechanism that is present in all of the Bifidobacteria for colonisation and persistence in the gut,” said O'Connell Motherway.
These perceived health benefits of Bifidobacteria have led to their widespread incorporation in infant food formulations and other health-promoting probiotic foods.
But, despite the high commercial and scientific interest in probiotics, fundamental knowledge is still scarce regarding the exact molecular mechanisms by which Bifidobacteria contribute to host health and well-being.
The researchers said that such knowledge is essential to scientifically explain the purported health benefits, and support the inclusion of such bacteria as probiotics in functional foods.
O'Connell Motherway added that the pili could possibly act as signalling molecules, which may begin to explain some of the reported health benefits of the probiotics, however she added that such signals have not yet been demonstrated.
“If we can demonstrate that the pili adhere to something in epithelial cells, then perhaps they could signal through those epithelial cells to the immune system,” she said.
The team will now focus on determining the full functions of the pili, in addition to exploring ways in which they are regulated and activated.
Source: Proceedings of the National Academy of Sciences (PNAS)
Published online ahead of print, doi: 10.1073/pnas.1105380108
“Functional genome analysis of Bifidobacterium breve UCC2003 reveals type IVb tight adherence (Tad) pili as an essential and conserved host-colonization factor”
Authors: M. O’Connell Motherway, A. Zomer, S.C. Leahy, J. Reunanen, F. Bottacini et al