U.S. Department of Energy

Pacific Northwest National Laboratory

Vitamin Sustainability in Diverse Microbial Communities

A hydrothermal spring in the Mammoth Hot Springs area of Yellowstone National Park.

The Science                      

In a recent study, scientists at Pacific Northwest National Laboratory (PNNL) observed two microbial communities to determine how they support diverse members unable to produce vitamin B-related enzyme cofactors, which are necessary for survival.  

The Impact

Their findings, published in ISME Journal,include evidence of a potential mechanismfor direct symbiosis using bi-directional transporters. Direct symbiosis occurs when a microorganism synthesizes excess vitamins and exports them for use by others in the community. In this study, reseachers observed that bi-directional transporters were preferentially found in organisms that could produce the vitamins. This could allow the producers to share vitamins with community partners in a controlled manner.

Additionally, researchers observed that different organisms are capable of salvaging different precursors in order to produce the vitamins they need. B vitamin cofactors are complex chemicals and require many steps for their synthesis, thus producing many intermediates. Salvaging intermediates can save organisms energy. While the intermediates produced in the later steps would save the most energy, the researchers found organisms that salvage both early and late intermediates are likely to avoid competition. Put simply, organisms take alternate routes to obtain precursors for the vitamins they need. It’s a mechanism for dividing labor within the community, saving all members energy and competitive stress.

The findings have important implications for the cultivation of microbes from environmental samples. When cultivating uncharacterized microbes, the researchers advise supplementing the growth medium with additional cofactor precursors to support growth of microbes unable to salvage the common vitamins.

Summary

In this study, scientists observed that the residents of microbial communities use a division-of-labor principle in order to sustain diverse members unable to produce essential vitamins for survival. There are two mechanisms for release of—or sharing—B vitamin precursors. The first, passive exchange, occurs with the death of a cell. As the cell breaks down, it releases a precursor that benefits consumers within the community. The second mechanism, direct symbiosis, occurs when producers synthesize excess vitamins and export them for use by community consumers.

Many microorganisms are unable to synthesize essential B vitamin-related enzyme cofactorsde novo. Scientists want to better understand the underlying mechanisms by which such microbes survive in multi-species communities. In the PNNL study, a previously reported, nearly complete genome sequence of two unicyanobacterial microbial consortia of around 19 members each enabled researchers to predict producers and consumers of precursors within the microbial community. In addition to these predictions, however, were additional discoveries about their ability to adapt based on the diversity of community members. 

The researchers observed that microbial consortia, collected from microbial mats in a 2014 study, maintain stable membership in their community despite a lack of vitamins in their environment. In fact, the consortia—a kind of microbial village of multiple species—are actually “neighborly.” 

Results of the study support for the first time the concept of syntrophic partnership based on vitamin exchange and suggest mechanisms, such as bi-directional transporters and salvaging of alternate vitamin precursors, that microbial communities use to retain members that need—but can’t produce—B vitamin-related enzyme cofactor precursors. 

Funding

This work was supported by the U.S. Department of Energy (DOE) Genome Sciences Program (GSP), Office of Biological and Environmental Research, and is a contribution of the Pacific Northwest National Laboratory (PNNL) Foundational Scientific Focus Area. Sequencing was done at the DOE Joint Genome Institute. Additional funding for work conducted by Dr. Rodionov was provided by the Russian Science Foundation

Publications

Margaret F. Romine, et al. “Underlying mechanisms for syntrophic metabolism of essential enzyme cofactors in microbial communities.” ISME Journal (2017). [doi: 10.1038/ismej.2017.2]

Date: 
February 2017
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