Survey of Genomes - 2 Bifidobacterium Strains

Time to talk about a good guy bacterium in the human gut! Stephanie Cipa from the 2019 Hiram College Genetics course tells the fascinating story of the bacterial genus Bifidobacterium that has evolved to live in the guts of humans and other mammals.

Welcome to Genomics Revolution. This is guest host Stephanie Cipa from the 2019 Hiram College Genetics course. I’m going to be talking about two strains of bacteria today; Bifidobacterium longum NCC2705 and Bifidobacterium longum ssp. longum 35624, previously known as Bifidobacterium infantis 35624. From here out I will be referring to them as B. longum 2705 and B. longum 35624. Lets dive right into it! 

B. longum has one circular chromosome made up of about 2,256,646 base pairs. In B. longum 2705 this creates up to 1,725 proteins. To really understand this bacteria I’m going back to the start of all our human lives, infancy. Babies are cute, squishy, and full of B. longum. In 1899, French pediatrician, Henry Tissier, observed a y-shaped microorganism in the stool of an infant with diarrhea. This microorganism turned out to be B. longum 35624, a strain strongly present in the gastrointestinal tract of babies. These bacteria are mostly anaerobic, gram positive microorganisms that are very helpful to us. Bacterium in the Bifidobacteriaceae family live in the guts of humans and help with digestion. While heavily present in babies, the population of B. longum diminishes over time due to the addition of many other gut microbes that we gain as we mature. B. longum is believed to be acquired by breastfeeding as the mother passes on helpful bacteria to the baby or during birth when the baby passes through the vagina, another location where this bacteria is known to live. These bacteria help by breaking down “nondigestable” plant polymers and oligosaccharides. The result of their fermentation is lactic and acetic acid, two products that help maintain intestinal pH as well. They can also limit the growth of harmful bacteria like E. coli. Understanding bifidobacterium helps us understand how it works with other bacteria in our guts to digest food and how it helps maintain homeostasis.

Many positive results have come from the discovery of B. longum. In 1907, Elie Metchnikoff suggested that this bacteria could be beneficial as a probiotic. It was one of the first to be considered for this role. Probiotics are supplements of live bacteria believed to be helpful for digestion and gut health. B. longum is believed to help bad bacteria pass through the gut easier and ease constipation and diarrhea. The most popular probiotic for Bifidobacterium is B. longum 35624, the strain from infants. It is marketed under the name “Align” and claims to be a purified strain of bifidobacteria meant for every day consumption. Of course there are hundreds of other products out there if this brand doesn’t “align” with your tastes!

Sequencing this genome in 2002 revealed to researches just how well B. longum have adapted to live in the human gut. They found multiple sequences coding for large proteins specialized for catabolism on a variety of oligosaccharides. A few of these proteins appeared to be specialized for “nondigestible” plant polymers. Because of the range of catabolic capabilities, B. longum appear to be well suited for life in the gastrointestinal tract. It also helps them compete with other bacteria present in the gut and may account for why we contain this bacteria from infancy to death.  Furthering these findings in 2007, another team of researchers discovered the sequences for 19 permeases in B. longum 2705 all meant for different carbohydrates. Amongst the genes were permeases for lactose, maltose, fructooligosaccharides, and more.  Again this just shows how well this bacteria has adapted to our personal gut jacuzzi of bacteria and digesting food. 

One more remarkable discovery that stemmed from genome exploration was the link between human breast milk and substrates for enzymes B. longum creates in infant guts. Essentially, researchers analyzed human breast milk and enzymes secreted by B. longum and found that 5 of the most abundant oligosaccharides in the milk were the preferred substrates for those enzymes. The researchers believed this to be an example of coevolution. This means that as humans and B. longum evolved, they effected each other’s evolution. This is fascinating to me because it has taken millions of years for this relationship between human and bacteria to perfect itself. They mutually benefit from this relationship because the bacteria digests abundant milk molecules, making it a strong competitor to survive in the gut, and the infant benefits by being able to digest the breast milk.

All three of these discoveries highlight just how extensively B. longum has evolved and adapted itself to fit into the highly specific environment that exists in the human gastrointestinal tract. Not only does it live there, but it also digests molecules and improves the health of the gut as well. These discoveries help scientists understand how and why certain relationships exist in the world. Not many people would consider the importance of a tiny bacteria for the overall health of a human. But, as B. longum shows us, sometimes it’s the tiny guys who make all the difference and the next time you’re using the restroom and it all goes according to plan, make sure you thank your gut bacteria for all the help in making it possible.

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