SANTA CRUZ, CA--Scientists have discovered an unusual symbiosis between tiny single-celled algae and highly specialized bacteria. Their partnership plays an important role in marine ecosystems, fertilizing the oceans by taking nitrogen from the atmosphere and "fixing" it into a form that other organisms can use.
Details of the symbiosis, published in the September 21 issue of Science, emerged from the investigation of a mysterious nitrogen-fixing microbe with a drastically reduced genome. First detected in 1998 by Jonathan Zehr, a professor of ocean sciences at the University of California, Santa Cruz, it now appears to be the most widespread nitrogen-fixing organism in the oceans. The microbe belongs to a group of photosynthetic bacteria known as cyanobacteria, but it lacks the genes needed to carry out photosynthesis and other essential metabolic pathways. Apparently, its association with a photosynthetic host cell makes those genes unnecessary.
"The cyanobacterium is a nitrogen-fixer, so it provides nitrogen to the host cell, and the host cell provides carbon to the cyanobacterium, which is lacking the metabolic machinery to get its own carbon," said Anne Thompson, a lead author of the paper and postdoctoral researcher in Zehr's lab at UC Santa Cruz. Rachel Foster of the Max Planck Institute for Marine Microbiology is the other lead author and contributed equally to this work.
Although the partners in the symbiosis have not been grown in the laboratory, Zehr's team and their collaborators have been able to characterize both partners using cell sorting, gene sequencing, and other techniques. The host cell is a type of single-celled algae in a class known as "prymnesiophytes," which are found throughout the world's oceans. In seawater samples sorted by flow cytometry, which separates cells by size and color, the host cells were discovered among the "photosynthetic picoeukaryotes," a mixed population of tiny single-celled alga
|Contact: Tim Stephens|
University of California - Santa Cruz