Beneficial bacteria in human gut

Introduction

The gastrointestinal (GI) tract in humans is a specialized and adaptable organ system. It not only plays a crucial role in digesting and absorbing nutrients but also supports one of the most intricate microbial communities identified in science, known as the gut microbiota.
This microbiota is a large and varied collection of microorganisms, which encompasses bacteria, archaea, viruses (notably bacteriophages), and eukaryotic microbes, including yeasts and protozoa. Of these microorganisms, bacteria are the most prevalent and thoroughly investigated group, making up about 90 to 95 % of the total microbial population found in the gut.
Only a small number of phyla are present, which includes over 160 species. The main gut microbial phyla are Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Fusobacteria, and Verrucomicrobia, with Firmicutes and Bacteroidetes making up 90% of the gut microbiota.
The Firmicutes phylum contains more than 200 different genera, including Lactobacillus, Bacillus, Clostridium, Enterococcus, and Ruminicoccus. Among these, the Clostridium genera account for 95% of all Firmicutes. The Bacteroidetes phylum features key genera like Bacteroides and Prevotella. Actinobacteria, on the other hand, is less common and is mainly represented by the Bifidobacterium genus.

The main gut microbial phyla are:

Firmicutes

Prokaryotic cell with strong cell wall. Gram positive bacteria The Firmicutes phylum consists of over 200 different genera, such as:

Key Genera:

Bacillus: Bacteria that can form spores can endure tough environments and remain alive when they enter the intestines. They generate enzymes like proteases and amylases that help with digestion. Certain types create antibacterial substances called bacteriocins, which prevent harmful bacteria. They activate the immune system and support the health of the gut lining. Bacillus coagulans is a well-known probiotic found in dietary supplements aimed at improving gut health.
Clostridium: Clostridium butyricum creates butyrate, which is a short-chain fatty acid (SCFA) important for:
- Feeding cells in the colon.
- Decreasing inflammation.
- Improving the strength of the gut barrier.
- It aids T-regulatory cells, which help to keep immune tolerance and stop autoimmune reactions.
Enterococcus: Certain strains serve as probiotics, particularly in supplements for both animals and humans. They help fight off harmful bacteria by sticking to the walls of the intestines and making substances called bacteriocins. They boost natural immune responses and strengthen the function of the intestinal barrier. They play a role in breaking down food carbohydrates and creating small amounts of vitamins.
Lactobacillus: A highly recognized group of probiotics. Converts sugars and lactose into lactic acid, which decreases gut pH and prevents the growth of harmful organisms. Generates bacteriocins and challenges pathogenic bacteria. Boosts mucosal immunity within the gut and modulates immune activities. Assists in the digestion of lactose and alleviates symptoms associated with lactose intolerance.
Ruminococcus: Crucial contributor to the breakdown of fibers, especially resistant starch and intricate plant polysaccharides. Creates short-chain fatty acids, notably butyrate and acetate. Facilitates the proliferation of other advantageous microorganisms through cross-feeding dynamics. Enhances the health of the intestinal barrier and overall metabolic wellness. Aids in the diversity of gut microbes, which is linked to improved immune response.

Bacteroidetes

Gram–negative, non-spore forming, rod shaped bacteria. 27 proteins present in most species of phylum Bacteroidetes. Phylum Bacteroidetes are divided into classes that include:

Key Classes:

Bacteroidia: The most prevalent and recognized group within the human gastrointestinal tract. Predominantly represented by the Bacteroides genus, featuring species such as Bacteroides fragilis and B. thetaiotaomicron, among others.
Flavobacteriia: Predominantly found in water-based settings, they are not prevalent in the human gastrointestinal tract but may occur temporarily as a result of dietary choices or surrounding conditions. Certain species can be identified within the microbiota of the mouth and skin.
Sphingobacteriia: Called for their capability to create sphingolipids, which are uncommon in bacteria but crucial for communication and defense in human cells. Present in small quantities in the intestines, but could have controlling functions: Interact with the immune system of the host.

Actinobacteria

Filamentous, road shaped, gram positive. Some species within the phylum Actinobacteria include:

Notable Species:

Lamia majanohamensis: Iamia-like bacteria have been discovered in both human and animal intestines, although in small quantities. These bacteria may play a role in breaking down complex carbohydrates and organic substances. They might also enhance the diversity of bacteria and help maintain stability within the gut ecosystem.
Olsenella: As a component of the microbiota within the oral cavity, this microorganism is also found in the gut and vaginal microbiomes. It has the ability to ferment carbohydrates, generating lactic acid and short-chain fatty acids (SCFAs). This function could contribute to sustaining a lower pH, which in turn may inhibit the proliferation of harmful bacteria.
Bifidobacterium: Bifidobacteria constitute a natural component of the microbiota within the colon. They play a crucial role in sustaining a beneficial equilibrium by competing with detrimental bacteria for nutrients and attachment points on the gut lining. These bacteria are responsible for the degradation of complex carbohydrates, fibers, and oligosaccharides, such as those found in breast milk or specific foods, transforming them into short-chain fatty acids (SCFAs), predominantly acetate and lactate. These SCFAs: Supply energy to colonic cells.Reduce intestinal pH, thereby hindering pathogens.

Proteobacteria

Gram negative, Non-spore forming, motile with flagella. Phylum Bacteroidetes are divided into classes that include:

Key Genus:

Escherichia: Produces vitamin K2, which plays a crucial role in bone health and the coagulation of blood. Aids in the absorption of oxygen within the intestines, creating an anaerobic setting that benefits strict anaerobes. Can inhibit the establishment of harmful microorganisms by means of competitive exclusion. Certain probiotic strains, such as E. coli Nissle 1917, are utilized for addressing ulcerative colitis enhancing the balance of gut microbiota controlling symptoms of diarrhea and irritable bowel syndrome.

Fusobacteria

Rod shaped, no-spore forming, non- motile, gram negative.

Important Species:

Fusobacterium nucleatum: Assists in the development of microbial biofilms within the gastrointestinal tract by connecting both Gram-positive and Gram-negative bacteria. May enhance microbial diversity through the support of colonization by other advantageous anaerobic organisms.
Fusobacterium mortiferum: Might assist in the breakdown of amino acids and proteins within the colon. Could provide indirect aid in the recycling of nutrients in the microbiome. Fusobacteria contribute to a well-functioning gut microbiome, yet their effects vary based on the specific strain, the condition of the host, and the overall balance of microbes. In instances where they exist in low to moderate quantities, certain species can aid in maintaining a healthy gut environment.

Properties of Beneficial Gut Bacteria

Non-pathogenic: These organisms do not induce illness in people with healthy immune systems.
Survive stomach acid and bile: They endure the extreme environment found within the digestive system.
Stick to the intestinal wall: They adhere to the lining of the intestines, contributing to the establishment of stable ecosystems.
Fight harmful microbes: They inhibit detrimental bacteria by vying for available space and producing natural antibiotics.
Digest fiber: They decompose plant fibers, resulting in the generation of beneficial substances such as short-chain fatty acids.
Make vitamins: They generate essential vitamins, including Vitamin K and various B vitamins.
Boost immunity: They assist in training and balancing the body’s immune response.
Protect the gut lining: They enhance the integrity of the gut barrier, preventing conditions like “leaky gut.”
Help with metabolism: They aid in regulating blood sugar levels, fat metabolism, and energy generation.
Connect with the brain: They create substances that can influence mood and mental well-being, contributing to the gut-brain connection.

Conclusion

Helpful microorganisms within the human digestive system are essential for upholding digestive wellness, improving nutrient uptake, and ensuring a balanced microbial community in the gut.
These probiotics bolster the immune defenses, shield against deleterious pathogens, alleviate inflammation, and facilitate the synthesis of vital metabolites such as short-chain fatty acids.
By encouraging the proliferation of these advantageous bacteria through proper nutrition and probiotic supplements, we can enhance gut performance, strengthen immune reactions, and lower the likelihood of gastrointestinal and systemic illnesses, thereby promoting overall health and well-being.

Reference and Sources

https://pmc.ncbi.nlm.nih.gov/articles/PMC6351938/
https://pmc.ncbi.nlm.nih.gov/articles/PMC9787832/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4711186/
https://www.microscopemaster.com/actinobacteria.html
https://quizlet.com/873964090/microbiology-review-flash-cards/
https://quizlet.com/638717766/microbiology-final-chapter4-flash-cards/
https://www.microscopemaster.com/bacteroidetes.html

Beneficial Bacteria in Human Gut: An Overview