Bifidobacterium

Bifidobacterium is a genus of Gram-positive, nonmotile bacteria. These tiny organisms are often branched in their physical shape. They are ubiquitous inhabitants of the gastrointestinal tracts in mammals. Some strains have also been isolated from the mouth and the vagina.

Because they are so common in the gut, they are major components of the microbiota. This is the community of microorganisms living inside a host. Many people consume specific strains as probiotics to support their health.

These bacteria function through several complex biological mechanisms. They help improve immune system function and reduce inflammation in the body. Specifically, Bifidobacterium increases the presence of regulatory T cells. They also work to improve the intestinal barrier. Through carbohydrate fermentation, they produce essential metabolites like acetate and butyrate. These substances can help protect the body against various diseases. They also provide necessary nutrients for other key bacteria in the gut.

Metabolism is a central part of how these bacteria survive. Bifidobacterium uses a unique fructose-6-phosphate phosphoketolase pathway to ferment carbohydrates. Much research focuses on how they process oligosaccharides. These are specific types of carbohydrates found in different environments. Infant-associated species have evolved to ferment milk oligosaccharides. In contrast, adult-associated species use plant oligosaccharides. This allows them to thrive on the specific foods available in their habitats.

Oxygen levels also play a major role in their survival. Most Bifidobacterium are anaerobic, meaning they prefer environments without oxygen. This sensitivity often limits their use as probiotics to anaerobic habitats. However, some recent research shows certain strains exhibit oxic growth. Scientists classify these species into four distinct oxygen-related groups. These are O2-hypersensitive, O2-sensitive, O2-tolerant, and microaerophilic. The production of hydrogen peroxide is a primary factor that inhibits aerobic growth.

The history of these bacteria involves important scientific discoveries. In 1899, Henri Tissier isolated a bacterium at the Pasteur Institute in Paris. He noticed a Y-shaped morphology, which means "bifid." He named the bacterium "bifidus" based on this shape. In 1907, Élie Metchnikoff proposed that lactic acid bacteria are beneficial. He observed that Bulgarians lived long lives due to fermented milk. He suggested that eating these cultures could implant beneficial bacteria in the gut.

Bifidobacterium species vary greatly in their genetic makeup. Their genomes, or sets of genetic instructions, differ in size. For example, B. indicum has a genome of 1.73 Mb. Meanwhile, B. biavatii has a larger genome of 3.25 Mb. These sizes correspond to different numbers of protein-encoding open reading frames. Specifically, B. indicum has 1,352 and B. biavatii has 2,557. About 13.7% of identified genes in this genus encode enzymes for carbohydrate metabolism.

There is a strong connection between these bacteria and human development. An infant's gut is relatively sterile at birth. It then collects bacteria from the environment and the mother. Breast-fed infants are colonized by Bifidobacterium much earlier than formula-fed babies. In these infants, Bifidobacterium is the most common bacteria in the gut. As children eat solid foods, their microbiome diversity increases. By age three, the microbiome becomes more stable and diverse.

Clinical uses for Bifidobacterium are expanding in modern medicine. Adding these bacteria as probiotics can help treat ulcerative colitis. This can lead to improved rates of remission and maintenance. They also help regulate intestinal microbial homeostasis. They can inhibit pathogens that try to infect the gut mucosa. In infants, they may discourage the growth of Gram-negative pathogens. This happens because they help reduce the pH in the infant gastrointestinal tract.