Bacteriophage viruses spread essential vitamin B12 through microbial ecosystems by infecting and destroying bacteria, researchers at Virginia Tech in Blacksburg, Virginia, have discovered.
The findings, published in The ISME Journal, reveal an unexpected microbial food web where viruses act as microscopic recyclers by releasing nutrient stores trapped inside host bacterial cells.
Virginia Tech, officially known as Virginia Polytechnic Institute and State University, is a public research university located in Blacksburg, Virginia. The ISME Journal is a peer-reviewed academic journal published by Nature Portfolio on behalf of the International Society for Microbial Ecology.
Vitamin B12, known scientifically as cobalamin, is an indispensable nutrient for biological processes ranging from DNA synthesis and red blood cell formation to the proper functioning of the nervous system. However, its natural origin is extremely exclusive. Neither humans, animals, nor plants possess the metabolic capacity to produce it, leaving only a select group of bacteria and archaea equipped to synthesize the vitamin.
Because synthesizing cobalamin requires high metabolic energy consumption, most microorganisms have evolved to obtain the vitamin or its derivative compounds directly from their environment. This dependency creates a biological dilemma across habitats such as oceans, soils, and the human gut, as scientists previously could not explain why any microorganism would voluntarily release such a costly resource to feed neighboring species.
Viral destruction of bacterial cells
The study, led by Virginia Tech researchers Bryan Hsu and David da Silva Barreira, demonstrated that bacteriophages act as catalysts by breaking open bacterial cells and releasing the vitamin B12 trapped within them.
During the lytic infection cycle, a phage attaches to a bacterium, injects its genetic material, and hijacks cellular machinery to replicate until the host cell is entirely destroyed.
When the bacterial membrane ruptures, newly created viruses escape alongside the cell's accumulated internal contents. Proteins, sugars, DNA, and vital nutrients such as vitamin B12 spill out suddenly into the surrounding environment, becoming available to nearby microorganisms.
Experimental verification of nutrient sharing
To verify whether this viral nutrient release was decisive for the growth of other bacteria, the researchers conducted experiments in a controlled system containing two types of microorganisms: one capable of synthesizing vitamin B12 and one dependent on the vitamin but unable to produce it.
When the producer bacteria remained intact, the dependent species failed to thrive, proving that vitamin B12 does not naturally leak into the surrounding environment.
Only when phages were introduced to destroy the producer bacteria was vitamin B12 released in sufficient concentrations to sustain the population growth of neighboring bacteria.
To rule out the possibility that other released cellular components caused the growth stimulus, the team repeated the experiment using a genetically modified bacterial strain incapable of synthesizing cobalamin.
Although the viruses destroyed these modified bacteria and spilled their contents, the dependent microorganisms did not grow, confirming that vitamin B12 was the indispensable resource driving the growth.
Impact on human gut microbiota
The researchers reported that the discovery extends beyond laboratory cultures to exert significant impacts on bacterial groups in the human digestive tract and overall microbiota diversity.
The term microbiota refers to the community of trillions of microorganisms living within a specific environment, such as the human gut, where they play essential roles in digestion and immune health.
The targeted release of cobalamin by phages not only benefited individual species but also restructured the overall composition of microbial communities. It increased community diversity more effectively than adding vitamin B12 uniformly to the growth medium.
The study shows that the exact timing and location of nutrient release are as important as the nutrient itself. Viruses are no longer seen purely as destructive agents, but as microscopic recyclers that shape complex ecosystem dynamics by transferring vital resources from producers to dependent organisms across gut, soil, and ocean environments.
