There are more bacteria in your colon than people on Earth.

They make up your gut microbiome and steer everything from bloating to brain fog.

Get to know them and you can shift digestion, immunity and energy in your favour.

In this article, you will meet the leading microbial families, discover what each one does and see how food, medication and stress decide the health of your microbiome.

Guide to Phylum, Genus, and Species

Before diving into your bacterial residents, let's understand how scientists classify them. Think of Russian nesting dolls, where each smaller doll fits inside a larger one.

Phylum represents the biggest doll. It's a very broad grouping that includes thousands of different bacteria sharing basic structural features.

Genus is the smaller doll inside. It's like a family name shared by closely related species. For example, Bacteroides is a genus containing many different Bacteroides species.

Species is the smallest doll. It's one specific microbe with a two-word scientific name like Bacteroides fragilis. Each species has unique characteristics and functions.

In this article, you'll mostly see phyla for the big picture and genera or key species for finer detail. This approach helps you understand both the big and little players in your gut.

Most Common Phyla

Your gut microbiome contains several major bacterial groups. Two dominate most healthy adults, while others play supporting but important roles.

Firmicutes generally claim the largest share of your gut real estate. These bacteria excel at breaking down complex carbohydrates and producing beneficial compounds that nourish your colon cells.

Bacteroidetes rank as the second most abundant group. They're particularly skilled at digesting plant fibres and adapting quickly to dietary changes.

Proteobacteria exist at lower levels than the two above but still perform vital functions. This group includes both helpful residents and potential troublemakers when they overgrow.

Actinobacteria also maintain smaller populations but punch above their weight. They're especially important in early life and continue supporting your health into adulthood.

Minor but noteworthy groups include Verrucomicrobia and Fusobacteria. Though less abundant, these bacteria contribute unique functions to your gut ecosystem.

Now let’s zoom one level deeper and meet the specific genera that handle most of the day-to-day work in your gut.

Most Common Genera

Now let's meet the key players within each major phylum. These bacterial genera handle much of the heavy lifting in your digestive system.

Faecalibacterium stands out as a major butyrate producer. This beneficial compound calms inflammation throughout your body and serves as the preferred fuel for your colon cells.

Ruminococcus specialises in breaking down resistant starch and cellulose. These tough plant fibres would otherwise pass through your system unused, but Ruminococcus transforms them into useful nutrients.

Lactobacillus ferments sugars into lactic acid and produces several B-vitamins. You might recognise this genus from yoghurt and other fermented foods.

Clostridium clusters IV and XIVa represent diverse groups of short-chain fatty acid makers. Despite their intimidating name, these bacteria are generally beneficial and help maintain your gut health.

Bacteroides excels at degrading complex plant polysaccharides. This genus shifts its activity based on your diet, ramping up when you eat more plants and scaling back with processed foods.

Prevotella thrives on high-fibre, plant-rich diets. Its presence often signals long-term eating patterns rather than short-term dietary changes.

Escherichia includes the harmless E. coli strains that peacefully coexist in your gut. These bacteria produce vitamin K and tolerate oxygen near your gut lining better than most other residents.

Sutterella represents an emerging genus that scientists are still studying. Early research suggests it may play a role in immune modulation.

Bifidobacterium dominates infant guts where it digests milk oligosaccharides. These bacteria persist into adulthood, continuing to support your digestive health and immune function.

Now we’ve looked at the most common genera, let’s zoom one final step and discuss specific species that live in your gut.

Most Common Species

Beyond genera, certain bacterial species deserve special attention for their health benefits and abundance in healthy guts.

Faecalibacterium prausnitzii serves as an abundant marker of gut health. Low levels of this species often correlate with digestive problems and inflammatory conditions.

Bacteroides fragilis produces capsule molecules that train your immune system. This species helps your body distinguish between harmful invaders and beneficial residents.

Bifidobacterium longum and B. bifidum act as pioneer colonisers in infant guts. These species establish themselves early in life and often persist through adulthood.

Roseburia intestinalis represents another important butyrate-producing Firmicute. Like its cousin Faecalibacterium prausnitzii, this species supports colon health through beneficial compound production.

What These Microbes Actually Do

Your gut bacteria are probably your body's hardest workers. They're constantly busy doing jobs that keep you feeling good.

First up, they turn the fibre you eat into powerful compounds called short-chain fatty acids. Plus, they help calm inflammation and might even boost your mood.

Your bacterial friends also make vitamins for you. Things like vitamin K2 and B-vitamins that your body needs but can't always make enough of.

Another thing to know is that your gut bacteria actually train your immune system. They teach it the difference between good guys and bad guys, so your body doesn't overreact to harmless things.

Microbes also keep your gut barrier strong. Think of it like a selective bouncer that lets good stuff through but keeps the nasties out of your bloodstream.

How Your Microbiome Forms and Changes

Your gut bacteria aren't set in stone. They're constantly changing based on how you live your life.

When you're born, you get your first bacterial residents from your mum and surroundings. By the time you're a toddler, your gut community settles into patterns that can stick around for years.

What you eat has a massive impact on who lives in your gut. Plant-rich, high-fibre foods help beneficial bacteria like Bacteroides and Prevotella thrive. Processed foods do the opposite, reducing the good bacteria and limiting variety.

Medications can completely reshape your gut community. Antibiotics wipe out both good and bad bacteria, while other drugs like antacids can tip the balance in unexpected ways.

Your lifestyle matters too. Chronic stress tends to reduce beneficial species, while regular exercise helps maintain a healthier bacterial mix.

As you age, bacterial diversity often declines, especially if you've had lots of antibiotics. But maintaining healthy habits can keep your gut microbiome young and vibrant.

Conclusion

The key genera are Bacteroides, Faecalibacterium, Ruminococcus, Lactobacillus, Bifidobacterium, and Escherichia.

These bacteria handle the big jobs like digestion, immunity, and keeping your metabolism running smoothly.

Understanding them helps you make better choices about what you eat, how you live, and where you might need support.

If you’d like a simple daily habit that feeds your microbiome, try Cosmic Hue tea. Thousands already drink it on a daily basis to support their gut health.

Author: Manny is the founder of Fifth Ray and a certified Gut Health Coach. After battling Crohn's Disease for 16 years, he transformed his gut health through plant-based healing. His story has been featured on BBC, ITV, and Daily Mail.

Please note this information is for educational purposes only, not medical advice. Cosmic Hue is not intended to diagnose, treat, cure, or prevent any disease. Always consult your healthcare provider before making changes to your health routine.