Too Much Oxygen Undermines Vitamin K2 Output in Fermented Meat Bacterium

Vitamin K2, a family of fat-soluble molecules known to scientists as menaquinones, has quietly become one of the most sought-after bacterial products in food and health research. Among its variants, MK-7 stands out for its association with bone metabolism and cardiovascular health, and the industrial world has largely relied on fermentation to make it. A new study published in Applied Microbiology and Biotechnology has now revealed a counterintuitive twist in this story: for at least one food-grade bacterium, the very ingredient that boosts vitamin K2 output in other microbes—oxygen—may actually work against it. Researchers at the Vrije Universiteit Brussel found that high oxygen exposure caused intracellular MK-7 levels to fall in Staphylococcus shinii IMDO-S216, a strain isolated from fermented meat, and their transcriptomic data point to oxidative degradation rather than a shutdown of biosynthesis as the culprit.

The strain at the center of the study belongs to a recently described species that is genetically close to Staphylococcus xylosus, a bacterium long familiar to food fermenters. S. shinii IMDO-S216 was grown under high oxygen supply in brain heart infusion medium at pH 7.0 and 30 degrees Celsius for 48 hours, conditions chosen to probe how aeration shapes menaquinone production in staphylococci—a group about which far less is known on this front than the lactic acid bacteria and Bacillus species, where oxygen has been shown to favor vitamin K2 yields. By tracking MK-7 concentrations over time and pairing those measurements with RNA sequencing, the team could watch both the chemistry and the gene expression of the cells as they responded to the oxygen-rich environment.

The central observation was deceptively simple. As the cultivation proceeded, the amount of MK-7 inside the cells steadily decreased, while the concentration found in the surrounding supernatant remained stable. That pattern matters because it rules out one obvious explanation: if the bacteria had simply stopped making menaquinones, the decline would likely be accompanied by changes in the expression of the genes that build them. Instead, the researchers found no differential expression of the MK-n biosynthetic genes during the decline. The production machinery, in other words, appeared to keep humming along even as the product inside the cells was disappearing.

What the transcriptomes did show was a loud and consistent oxidative stress signature. Genes associated with coping with reactive oxygen species were upregulated as the experiment progressed, including cydAB, which encodes components of the respiratory chain, and a suite of carotenoid-related genes—crtO, crtP, crtQ, and crtM—that bacteria typically deploy to shield themselves from oxidative damage. Alongside these, the cells ramped up expression of ROS-detoxifying genes such as sodA, katB, katC, bsaA, and ohrA, which together handle superoxide radicals, hydrogen peroxide, and organic peroxides. To the researchers, this coordinated defensive response was the fingerprint of an environment in which oxygen-derived reactive species were actively attacking cellular components, and menaquinones were among the casualties.

That interpretation fits with the peculiar chemistry of menaquinones themselves. Vitamin K2 is not merely a vitamin; in bacteria it serves as an electron carrier in the respiratory chain, shuttling electrons between membrane complexes. That role places menaquinones squarely in the path of redox reactions that can generate dangerous intermediates. Quinones, the chemical class to which menaquinones belong, can cycle between oxidized and reduced states, and in doing so they can spawn semiquinone radicals and superoxide anions—reactive molecules that damage proteins, DNA, and lipids. The study’s authors hypothesized that this redox activity is precisely what initiates the degradation of the menaquinone pool under high aeration.

A single gene emerged as a possible trigger for that destructive cascade: qorA. This gene, which is linked to the formation of semiquinone radicals and superoxide anions from quinones, was proposed by the researchers as a contributor to the initial stages of menaquinone degradation in S. shinii IMDO-S216. The idea is elegant in its irony: the very redox chemistry that makes menaquinones useful as electron carriers may, under oxygen-saturated conditions, turn them into their own worst enemies, with qorA-mediated reactions setting off a chain of oxidative events that dismantles the vitamin K2 molecules the cell has worked to produce.

The study also uncovered a subtle shift in the composition of the menaquinone pool. Over the course of the 48-hour cultivation, the relative abundance of the MK-6 to MK-7 ratio increased over time. Because MK-6 and MK-7 differ in the length of their isoprenoid side chains, a rising MK-6/MK-7 ratio suggests that the longer-chain variant is being disproportionately affected. The authors interpret this trend as potentially reflecting an adaptive survival strategy in the bacterium—a way of reshaping its quinone portfolio to better withstand the oxidative pressures of a high-oxygen lifestyle. Whether shorter-chain menaquinones are inherently more robust, or whether the shift reflects selective degradation of MK-7, remains a question for future work.

The practical implications reach into both food science and biotechnology. Fermented meats rely on coagulase-negative staphylococci to develop color, flavor, and safety, and these organisms contribute to the vitamin K2 content of the final product. If high oxygen exposure erodes intracellular MK-7 in such strains, then process design—from mincing and mixing to drying and packaging—could influence not only the sensory qualities of fermented foods but also their nutritional profile. For producers aiming at microbial vitamin K2 as an ingredient, the findings caution against assuming that lessons learned from Bacillus or lactic acid bacteria will transfer directly to staphylococci. Oxygen management, which boosts yields in those well-studied producers, may need to be approached differently when the production host is a meat-derived Staphylococcus.

Methodologically, the study demonstrates the value of pairing analytical chemistry with transcriptomics. Measuring MK-7 in the cells and the supernatant separately revealed where the vitamin was going; RNA sequencing revealed why. Without the gene expression data, the decline in intracellular MK-7 could have been misread as a biosynthetic failure. With it, the picture flipped: the biosynthetic genes were quiet, the stress genes were loud, and the most parsimonious explanation was that the vitamin was being made and then destroyed. The work also highlights the importance of the electron transport chain as a lens for understanding vitamin K2 metabolism, since the molecule’s day job as an electron carrier is inseparable from its vulnerability to oxidative attack.

There remain open questions. The study was conducted in brain heart infusion medium under laboratory conditions, and the behavior of S. shinii IMDO-S216 in a real fermented meat matrix—with its lower oxygen tensions, competing microbes, and complex chemistry—may differ. The precise molecular mechanism by which qorA and associated redox reactions initiate menaquinone degradation has been hypothesized rather than fully demonstrated, and the adaptive significance of the shifting MK-6/MK-7 ratio invites direct testing. Still, the core message is clear and actionable: for this food-grade staphylococcus, high aeration disfavors MK-7 production, and the loss is driven by oxidative degradation rather than by any failure of the biosynthetic apparatus. For anyone hoping to coax more vitamin K2 out of fermented foods or microbial cell factories, the answer may lie not in pumping in more air, but in protecting the precious quinones from the air that is already there.

Subject of Research: Effect of high oxygen exposure on vitamin K2 (menaquinone) production and degradation in the food-grade bacterium Staphylococcus shinii IMDO-S216

Article Title: Vitamin K2 production by Staphylococcus shinii IMDO-S216 is affected by high oxygen exposure

Article References: Bonaldo, F., Pradal, I., Debrus, V., Duverger, C., Mangelings, D., Weckx, S., & Leroy, F. (2026). Vitamin K2 production by Staphylococcus shinii IMDO-S216 is affected by high oxygen exposure. Applied Microbiology and Biotechnology. https://doi.org/10.1007/s00253-026-14038-y

Image Credits: AI Generated

DOI: 10.1007/s00253-026-14038-y

Keywords: vitamin K2, menaquinones, MK-7, Staphylococcus shinii, oxygen, oxidative stress, transcriptomics, RNA-seq, biosynthesis, fermented meat, electron transport chain, reactive oxygen species