You already know fermented foods are good for you. But have you ever wondered why a jar of sauerkraut has more B12 than the raw cabbage it came from? The microbes doing the fermenting aren’t just breaking food down, they’re actively building vitamins your body needs.
Besides vitamins, microbes also make other organic acids and metabolic compounds that are healthy for the human body. Microbial vitamin production can be found with uncooked (raw) foods where these microbes are naturally present and also in fermented foods where these microbes can grow.
Here’s a strain-by-strain look at which microbes make which vitamins, and where you’ll actually find them:
Matt’s Note:
The vitamin composition of a food is directly tied to the microbes in that food that have physically made the specific vitamins. Yes, technically you could look at the vitamin composition of a food item and make predictions to which microbes would naturally be present in those foods.
For example: pork has more B1 than other meats which means that we can find more B1-making microbes in pork than in other meats. Alternatively, vitamin B9 or folate is more found in leafy greens which means that we’ll likely find B9-making microbes on leafy greens.
If you are struggling with a specific vitamin deficiency, consider looking up the associated microbes that help make these vitamins to help with symptoms.
Vitamin B1 (Thiamine)
Thiamine is essential for energy metabolism, and specific bacteria can synthesize it both in fermented foods and in the gut.
- Microbes Involved: Lactobacillus plantarum, Lactobacillus fermentum, and Escherichia coli. (List non-exhaustive, the most common microbes are listed. This applies to every vitamin listed)
- Process: These microbes possess enzymes needed to assemble thiamine’s molecular structure, which they use as a cofactor for their own metabolism. In fermented foods like sourdough bread, cheeses, and kefir, Lactobacillus strains synthesize thiamine during fermentation. This allows for natural thiamine enrichment in these foods.
Vitamin B2 (Riboflavin)
Riboflavin plays a crucial role in cellular energy production and supports enzyme functions in both humans and microbes.
- Microbes Involved: Lactobacillus fermentum, Lactobacillus reuteri, and Bacillus subtilis
- Process: These microbes create riboflavin to meet their own metabolic needs. This vitamin is synthesized in the metabolic pathways where nutrients are broken down, and it accumulates within the microbial cells or is released into the surrounding medium in certain foods, such as yogurt, cheese, and fermented vegetables.
Vitamin B3 (Niacin)
Niacin is essential for DNA repair and energy metabolism. In the human diet, niacin-rich fermented foods can be an excellent source of this vitamin.
- Microbes Involved: Lactobacillus plantarum, Lactobacillus rhamnosus, Propionibacterium freudenreichii
- Process: Microbes synthesize niacin through their tryptophan metabolic pathways, a process linked to cellular energy production. This pathway is activated by the demands of microbial growth, and niacin is then released into fermented products like sauerkraut, kefir, and sourdough.
Vitamin B6 (Pyridoxine)
Pyridoxine is involved in amino acid metabolism and neurotransmitter synthesis.
- Microbes Involved: Lactobacillus plantarum, Lactococcus lactis, Propionibacterium freudenreichii
- Process: Microbial synthesis of vitamin B6 happens in the biosynthetic pathways of amino acid metabolism, where the bacteria generate it as a coenzyme for their cellular reactions. Fermented foods like cheese, kimchi, and miso contain vitamin B6 from these microbes, contributing to their nutritional value.
Vitamin B7 (Biotin)
Biotin, also known as vitamin B7 or vitamin H, is essential for fatty acid synthesis and metabolic health.
- Microbes Involved: Lactobacillus plantarum, Bifidobacterium bifidum
- Process: These microbes synthesize biotin as a coenzyme for their own metabolic needs, especially in fatty acid synthesis. Fermented foods like yogurt and sauerkraut contain biotin, and gut microbes contribute to biotin availability within the human body.
Vitamin B9 (Folate)
Folate is vital for DNA synthesis and cell division. Certain microbes can synthesize folate both in the human gut and in fermented foods. Folate for foliage means that lots of B9 availability comes from leafy greens.
- Microbes Involved: Lactobacillus plantarum, Lactococcus lactis, Propionibacterium freudenreichii
- Process: In folate biosynthesis, microbes convert precursor compounds into active forms of folate through a complex series of enzyme-driven steps. In fermented dairy products, especially cheeses and kefir, these microbes add folate to the product, making it more nutrient-dense.
Vitamin B12 (Cobalamin)
Vitamin B12 is essential for red blood cell formation and neurological health. Unlike other B vitamins, B12 synthesis is exclusive to bacteria and archaea.
- Microbes Involved: Propionibacterium freudenreichii, Lactobacillus reuteri, Bifidobacterium longum (in small amounts)
- Process: Microbes synthesize B12 through a complex pathway requiring cobalt, an element crucial for the vitamin’s core structure. Fermented foods such as cheese and fermented soy (like natto) contain B12 from these microbes. Some probiotic supplements also contain Propionibacterium specifically for its B12-producing capability.
Vitamin K2 (Menaquinone)
Vitamin K2 is important for bone health and cardiovascular function, and its production by microbes makes it accessible through specific foods and gut microbiota.
- Microbes Involved: Bacillus subtilis, Lactococcus lactis, Escherichia coli
- Process: Menaquinone is synthesized as part of these microbes’ cellular respiratory pathways, particularly in anaerobic conditions (low oxygen). In foods like natto and certain cheeses, Bacillus subtilis and other bacteria produce vitamin K2 during fermentation, making these foods potent dietary sources of the vitamin.
Vitamin C (Ascorbic Acid)
While vitamin C production by microbes is relatively limited, certain species can contribute small amounts in particular environments.
- Microbes Involved: Gluconobacter oxydans, Acetobacter spp.
- Process: Microbial synthesis of vitamin C is limited and is mainly observed in specific fermentative conditions. For instance, some vinegars, especially those made with Acetobacter, retain trace amounts of vitamin C due to the metabolism of these bacteria.
Fermentation and Gut Microbiota: Dual Sources of Microbial Vitamins
In fermented foods, bacteria and yeasts synthesize these vitamins as they metabolize sugars, proteins, and other compounds. For example, yogurt, kefir, kimchi, natto, and certain cheeses naturally contain higher vitamin levels due to microbial activity.
In the human gut, specific microbes also produce vitamins, with some being absorbed directly by the gut lining. This dynamic happens primarily in the colon, where anaerobic bacteria can contribute to vitamin K2, B12, and biotin synthesis. However, because the absorption of these microbial vitamins in the gut is complex and not fully reliable, fermented foods often provide a more consistent dietary source.
Understanding how microbes produce vitamins highlights their integral role in both food nutrition and gut health, especially as part of an overall diet that includes fermented foods and diverse fiber sources to nourish beneficial gut flora.
B Vitamins and Their Roles in Gut Health PMID: 35744686
Metabolism of Dietary and Microbial Vitamin B Family in the Regulation of Host Immunity