Like humans and other animals, modern plants depend on and interact with their microbiomes - communities of partner microorganisms that provide nutritional benefits to their hosts. Molecular and fossil evidence indicate that symbiotic microbes were critical to the ability of earliest plants to colonize land, thereby forming the basis for complex terrestrial ecosystems that have existed for the past several hundred million years. Yet our understanding of how early plant-microbe partnerships arose is sparse because the microbial associations of closely-related green algae are poorly known. Past study of such relatives has revealed the origin of many molecular, biochemical, physiological, structural, and reproductive features of the modern plants upon which humans depend. This project uses state-of-the-art genomic sequencing and computer data processing methods to infer microbial diversity and function in key algal-microbe and plant-microbe partnerships. These data are expected to reveal fundamental features of modern plant-microbe partnerships.

This project will extend knowledge of microbial diversity and function in natural ecosystems and illuminate plant evolutionary history. Many new gene sequences useful to the scientific community and new microbial species of potential utility are expected to be discovered. The project links to diverse educational activities, particularly the development of a new web resource designed for the general public, students, and researchers.

Project Report

Many people have become aware that the human body hosts thousands of microbial species that influence human health, together known as the human microbiome. Other animals and higher plants are also known to host diverse and beneficial microbial species, but the microbiomes of algae and simpler plants are poorly known. Yet such microbiomes are important because algae and simple plants are abundant today, affect society in diverse ways, and have played important roles in Earth's ecological history. In this project, we used state-of-the-art sequencing and analysis methods to describe the microbiomes of species key to understanding how the earliest plants benefitted from microbial associations. We learned that modern relatives of earliest plants consistently harbor several types of microbes that play essential roles in modern ecosystems: nitrogen-fixers, vitamin producers, methane oxidizers, and fungi. These microbes occur in mucilaginous biofilms on the surfaces of algal and plant cells, revealed by microscopic methods. The consistency of our results suggests that early plants likewise had the ability to form such microbial associations, which may have fostered plant success on land and and been inherited by modern plants. These results illuminate the past history of plants and their ancient environmental effects. Our results also indicate that modern algae commonly have microbiomes likely to play important, but previously unsuspected environmental roles. One such role is the oxidation of methane that naturally forms in aquatic systems into carbon dioxide that the algae may fix into organic compounds such as lipids. This process may reduce the amount of aquatic methane that escapes into the atmosphere and contributes to global warming. The common partnerships that occur between algae and microbial biofilms also suggest the possibliity of new applications in the area of clean energy technologies.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Simon Malcomber
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University of Wisconsin Madison
United States
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