Plate · Bacteroidota

species · NCBI 818

Bacteroides thetaiotaomicron

Its ID gene (16S) · each bar is one letter A C G T NCBI 16S

What's this?

Zoomed in: letters 115–138

Its ID gene: the stretch scientists read to tell microbes apart. Each bar is one letter of its DNA. Every species has its own order of letters, so the pattern works like a fingerprint. Close relatives share most of it.

16S rRNA gene, V4 region: the 253 letters between the standard primers (515F/806R), which are the same in every species. One reference sequence; strains can differ by a letter or two. NCBI NR_074277.1

Formerly Bacillus thetaiotaomicron.

Healthy guts69%

Samples16,618

Products0

Genome · 6.3 million letters · 43% G+C

Shortest we have Mycoplasmoides genitalium 0.6M

⋮ 2,251 shorter

Bacteroides average 5.0M

Bacteroides thetaiotaomicron 6.3M

⋮ 100 longer

Longest we have Bradyrhizobium altum 9.8M

Among the largest for a gut microbe: longer than 96% of the 2,354 we have genomes for.

Bigger genomes usually carry more tools: it can do 8 of the 13 things we track, more than most gut microbes. See what it can do →

43% G+C, higher than 37% of gut microbes.

To scale: if its ID gene were 1 cm long, its genome would stretch 42 meters. Yours would stretch 21 kilometers. One reference genome; strains vary. NCBI GCF_014131755.1

Lab traits Gram −Rod-shapedNon-motileAnaerobe

Also known as Bacillus thetaiotaomicronBacteroides fragilis subsp. thetaiotaomicronPseudobacterium thetaiotaomicronSphaerocillus thetaiotaomicron

Capabilities, not measurements of anyone's gut

What it can do

Makes

Can make propionate A short-chain fatty acid, mostly used by the liver.
Can make lactic acid What yogurt bacteria make; other microbes turn it into butyrate.

Eats

Can ferment fiber Breaks down dietary fiber that our own enzymes can't.
Can eat inulin A fiber in onions, garlic, leeks, chicory and bananas (also sold as FOS).
Can eat pectin A fiber in apples, citrus and other fruit.
Can use lactose The sugar in milk and dairy.

Not seen in its genomes: make butyrate, eat resistant starch, make B vitamins, make hydrogen sulfide, make methane.

All 13 capabilities and their evidence

Capability	Verdict	Genome analysis	Lab tests	Published research
Can make butyrate	Not seen	0 of 12 genomes	—	No papers
Can make propionate	Can	12 of 12 genomes	—	Papers say yes
Can make lactic acid	Can	12 of 12 genomes	—	Papers say yes
Can ferment fiber	Can	12 of 12 genomes	11 of 11 strains · strip test	Papers say yes
Can eat inulin	Can	12 of 12 genomes	—	Papers say yes
Can eat resistant starch	Not seen	0 of 12 genomes	—	No papers
Can eat pectin	Can	12 of 12 genomes	—	Papers say yes
Can use lactose	Can	12 of 12 genomes	2 of 2 strains	No papers
Can feed on gut mucus	Can	12 of 12 genomes	—	Papers say yes
Can change bile acids	Can	2 of 12 genomes	—	Papers say yes
Can make B vitamins	Not seen	0 of 12 genomes	—	No papers
Can make hydrogen sulfide	Not seen	0 of 12 genomes	—	No papers
Can make methane	Not seen	0 of 12 genomes	—	No papers

AGORA2 (Heinken et al. 2023) via VMH, CC BY 4.0 · BacDive (DSMZ), CC BY 4.0 · NJC19 (Lim et al., Scientific Data 2020), CC0

What’s typical · a description, not a comparison

In healthy guts

Everyone · 12,213 people · 129 studies

How common

Found in 69% of healthy people.

How big a slice of the gut

largest Segatella copri 6.2%
2nd largest Phocaeicola vulgatus 5.0%
3rd largest Faecalibacterium prausnitzii 4.7%
4th largest Bacteroides uniformis 3.2%
5th largest Agathobacter rectalis 2.5%
6th largest Alistipes putredinis 2.3%
7th largest Bifidobacterium longum 2.1%
8th largest Ruminococcus bromii 1.8%
⋮
top 50 Bacteroides thetaiotaomicron 0.5%
2,169 other microbes, each a sliver 56.1%
15.6%

On average, 0.5% of the microbes in a healthy gut: among the 50 largest slices.

By age and sex

Every group, drawn the same way. Only some samples record age or sex, so each group says how many people it comes from. Tap one to see it above.

By age

367 people · 17% carry it 0.4% of the microbes top 50

198 people · 5 studies 74% carry it 1.7% of the microbes top 20

57 people · 35% carry it 0.4% of the microbes top 50

1,283 people · 27 studies 80% carry it 0.7% of the microbes top 30

142 people · 15 studies 76% carry it 0.7% of the microbes top 30

By sex

2,063 people · 70% carry it 0.8% of the microbes top 30

1,530 people · 29 studies 66% carry it 0.8% of the microbes top 30

Compared within studies that had both

In conditions

Compared with healthy people in the same studies, it’s less common in 5 conditions and more common in 2 conditions. Only studies that had both are counted.

A difference is an association: it doesn’t mean this microbe causes, prevents or treats any of these.

Strongest first, then the biggest gap · Each figure is 10 people

Crohn's disease 1,313 people · 8 studies Less common in people with it Healthy 69% With it 55%
Colorectal cancer 475 people · 10 studies As many carry it in people with it Healthy 83% With it 89%
Carriers have about twice as much, in 6 of 7 studies (0.18% → 0.46% of their gut microbes).
Neuroblastoma 95 people · 2 studies Less common in people with it Healthy 55% With it 34%
Clostridium infections 24 people · 1 study Less common in people with it Healthy 100% With it 42%
Pancreatic cancer 24 people · 1 study More common in people with it Healthy 5.6% With it 58%
High blood pressure 50 people · 1 study More common in people with it Healthy 66% With it 94%
Cystic fibrosis 52 people · 1 study Less common in people with it Healthy 30% With it 5.8%
Atopic dermatitis 226 people · 1 study Less common in people with it Healthy 27% With it 14%

PubMed · human studies and reviews first

Recent research

All research on it

Observational Iranian journal of medical sciences · 2026
Integrative Metagenomic Analysis Reveals Human Gut Microbiome-Derived Candidate Non-invasive Biomarkers for Type II Diabetes Mellitus.
PubMed ↗
Review Virulence · 2026
Microbiome-mediated regulation of pathogen virulence: Molecular mechanisms and clinical implications.
PubMed ↗
Review International journal of molecular sciences · 2026
Intestinal Flora and Myocarditis: Potential Mechanisms and Therapeutic Strategies Affecting Disease Progression and Cardiac Function.
PubMed ↗
Observational The spine journal · 2026
Molecular traces of microbial cross-kingdom migration: from the gut ecosystem to the intervertebral disc microenvironment.
PubMed ↗
Observational JHEP reports · 2026
Alcohol-related liver disease disrupts bile acid homeostasis and gut microbial bile acid metabolism.
PubMed ↗

Source: PubMed, U.S. National Library of Medicine · 527 linked papers, last 10 years

Bacteroides thetaiotaomicron

What it can do

In healthy guts

Where these numbers come from

In conditions

Where these numbers come from

Also compared · 48 conditions

No meaningful difference · 48

Recent research