Bifidobacterium is a genus of gram-positive, nonmotile, often branched anaerobic bacteria. They are ubiquitous inhabitants of the gastrointestinal tract, vagina and mouth (B. dentium) of mammals, including humans. Bifidobacteria are one of the major genera of bacteria that make up the colon flora in mammals. Some bifidobacteria are used as probiotics. (source)

According to a Bangladeshi microbiota study published last month, poor vaccine efficacy is associated with systemic inflammation due to gut dysbiosis. Bifidobacteria were found a key factor in improving vaccine responsiveness. There are many known strains of bifidobacteria, some considered better than others. Bifidobacteria levels in the USA vary widely among individuals. Studies report much lower levels of bifidobacteria in children with autism. (source)

• Abundance associated with higher bacterial gene richness in the gut • Modulates local and systemic immune responses • Abundance lower in IBD • Abundance lower in IBS; low levels also correlate with symptom severity in IBS • Lower levels seen in type 2 diabetes, pediatric allergy, and autism • Increased levels in obese subjects compared to lean/overweight; infants with lower Bifidobacterium may have increased risk for weight gain in childhood • Abundance decreases after weight loss and gastric-bypass surgery (source)

“Overall, both of these microbes seem to be major players in the gut-brain axis. John Cryan, a neuroscientist at the University College of Cork in Ireland, has examined the effects of both of them on depression in animals. In a 2010 paper published in Neuroscience, he gave mice either bifidobacterium or the antidepressant Lexapro; he then subjected them to a series of stressful situations, including a test which measured how long they continued to swim in a tank of water with no way out. (They were pulled out after a short period of time, before they drowned.) The microbe and the drug were both effective at increasing the animals’ perseverance, and reducing levels of hormones linked to stress. Another experiment, this time using lactobacillus, had similar results. Cryan is launching a study with humans (using measurements other than the forced swim test to gauge subjects’ response).” (source)

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Christensenella minuta

Christensenella minuta is a heritable firmicute that is linked to leanness.

From The Most Heritable Gut Bacterium is… Wait, What is That?:

By studying 416 pairs of British twins, Julia Goodrich and colleagues from Cornell University have identified the gut microbes whose presence is most strongly affected by our genes. And chief among them was a mysterious bacterium called Christensenella minuta, the one and only member of a family that was discovered just three years ago.

Genetically and physically, it’s rather mundane. It’s yet another rod-shaped, oxygen-hating, nutrient-fermenting bacterium from the Firmicute dynasty—one of the two major groups in our guts. And yet, more than any other microbe, its presence in our body is strongly influenced by our genes. Christensenella also seems to sit at the centre of a large network of microbes; if it’s there, these others are likely to show up too. And it influences our weight: it’s more common in lean people, and it can reduce weight gain in mice.

All of these traits suggest that Christensenella might (emphasis on might) be a keystone species: one that wields a disproportionate influence upon the world around it. The term was first used to describe a starfish, whose absence could entirely change the nature of a seashore. It has since been used to describe sea otters, wolves, and mistletoe. These species might be relatively rare, but they are ecologically powerful. Perhaps Christensenella is similarly important in the world of our guts. And yet, until recently, no one even knew it existed.

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Roseburia is a genus of butyrate-producing, Gram-positive anaerobic bacteria that inhabit the human colon. Named in honor of Theodor Rosebury, they are members of the phylum firmicutes. Increased abundance of Roseburia is associated with weight loss and reduced glucose intolerance. (source)

• Abundance associated with higher bacterial gene richness in the gut • Less abundant in individuals with IBS, particularly constipation-predominant IBS • Counts lower in type 2 diabetics; trending inversely with plasma glucose • Lower in IBD and early-onset rheumatoid arthritis (as part of decreased E. rectale-C. coccoides group) (source)

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