Lactococcus lactis
What's this?
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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 252 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_040956.1
Formerly Lactobacillus xylosus.
Small for a gut microbe: longer than 34% of the 2,354 we have genomes for.
35% G+C, higher than 11% of gut microbes.
To scale: if its ID gene were 1 cm long, its genome would stretch 18 meters. Yours would stretch 21 kilometers. One reference genome; strains vary. NCBI GCF_003176835.1
What it can do
- Can make lactic acid What yogurt bacteria make; other microbes turn it into butyrate.
- Can make B vitamins Folate, B12, riboflavin and others.
- Can ferment fiber Breaks down dietary fiber that our own enzymes can't.
- Can use lactose The sugar in milk and dairy.
Not seen in its genomes or lab tests: make butyrate, make propionate, eat inulin, eat resistant starch, eat pectin, feed on gut mucus, change bile acids, 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 6 genomes | — | No papers |
| Can make propionate | Not seen | 0 of 6 genomes | — | No papers |
| Can make lactic acid | Can | 6 of 6 genomes | — | Papers say yes |
| Can ferment fiber | Can | 6 of 6 genomes | 0 of 25 strains · strip test Strip tests often miss fiber-eaters, so this doesn't override the genomes. | Papers say yes |
| Can eat inulin | Not seen | 0 of 6 genomes | 0 of 15 strains · strip test | No papers |
| Can eat resistant starch | Not seen | 0 of 6 genomes | — | No papers |
| Can eat pectin | Not seen | 0 of 6 genomes | — | No papers |
| Can use lactose | Can | 6 of 6 genomes | 18 of 23 strains | No papers |
| Can feed on gut mucus | Not seen | 0 of 6 genomes | — | No papers |
| Can change bile acids | Not seen | 0 of 6 genomes | — | No papers |
| Can make B vitamins | Can | 6 of 6 genomes | — | Papers say yes |
| Can make hydrogen sulfide | Not seen | 0 of 6 genomes | — | No papers |
| Can make methane | Not seen | 0 of 6 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
In healthy guts
Found in 11% of healthy people.
- 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 15% Lactococcus lactis 0.02%
- 2,169 other microbes, each a sliver 56.6%
- 15.6%
On average, 0.02% of the microbes in a healthy gut: larger than 85% of species’ slices.
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.
In conditions
Compared with healthy people in the same studies, it’s less common in 1 condition and more common in 1 condition. 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 peopleIn studies of how people live
Higher in vegetarians than vegans
Fackelmann 2025 · 21,561 people Landmark study
Higher in 3 of 4 cohorts
“Higher” is the study’s measure: on average, a bigger share of gut bacteria across everyone in the group, carriers or not. It isn’t how many people carry it. An association the authors report, measured once per person. It doesn’t mean a diet changes this microbe, or that the microbe affects health.
Recent research
Source: PubMed, U.S. National Library of Medicine · 1,094 linked papers, last 10 years
Strains studied
How much each strain has been studied in people, not whether it works. Many trials test a strain inside a blend, so those are counted apart, and reviews are summaries of trials, so they're never counted as more trials.
16 strains of L. lactis are named on product labels. 0 have human trials; 16 have none found yet, including Ll-23, which is in 64 products.
L. lactis Ll-23
In 64 products →No human trials found yet
L. lactis SD-5584
In 22 products →No human trials found yet
L. lactis HA-136
In 15 products →No human trials found yet
L. lactis UALl-08
In 9 products →No human trials found yet
L. lactis SD-5848
In 8 products →No human trials found yet
L. lactis R1058
In 5 products →No human trials found yet
L. lactis ATCC SD5584
In 3 products →No human trials found yet
L. lactis VPro41
In 3 products →No human trials found yet
L. lactis VPro42
In 3 products →No human trials found yet
L. lactis W58
In 3 products →No human trials found yet
L. lactis A200
In 2 products →No human trials found yet
L. lactis PXN 63
In 2 products →No human trials found yet
L. lactis UALL-8
In 1 product →No human trials found yet
L. lactis VPro17
In 1 product →No human trials found yet
L. lactis VPro34
In 1 product →No human trials found yet
L. lactis W19
In 1 product →No human trials found yet
Human trials, meta-analyses and systematic reviews naming the strain · animal and lab studies not counted · Data sources