Tiny microbe hints at cell interaction

RUTGERS (US) — A bucket of seawater and a single-celled marine animal are offering clues to what makes a cell healthy or unhealthy.

Using sophisticated new technologies, researchers sequenced the genomes of individual picobilophytes, tiny microbes first discovered in 2007 that—at less than 10 micrometers across—are some of the tiniest marine animals known to science.

“If we can peer inside the genome of a single cell and reconstruct its history, we can do that for many cells and figure out their interactions with other cells in the environment,” says Debashish Bhattacharya, professor of ecology, evolution, and natural resources at Rutgers.

“Our results demonstrate how single cell genomics opens a window into the natural drama that constantly takes place in each drop of seawater—a drama featuring predation, viral infections, and the divergent fate of close relatives,” says Ramunas Stepanauskas of the Bigelow Laboratory of Ocean Sciences. “The outcomes of this drama have profound effects on the lives of larger marine organisms, such as commercially valuable fish.”

Details appear in the journal Science.

Bhattacharya and Oscar Schofield, professor of marine science, are now working to apply these techniques to Antarctica alage. Some species traditionally found along the Western Antarctic Peninsula are dying off as the water warms, and others, not seen before there, are moving in.

If Bhattacharya and Schofield can sequence the genomes of those algae cell by cell, as he and Stepanauskas have done with picobilophytes, they might learn much more about how climate change has affected the ecosystem in that region. Bigelow Laboratory has analyzed more than150,000 individual microbial cells, shedding new light on the invisible majority of our planets biological diversity.

When picobilophytes were discovered in 2007, scientists believed they were photosynthetic—that is, that, like green plants, they converted carbon dioxide into food, using energy from sunlight.

But these tiny cells have been impossible to culture in the laboratory and this may have been because they were starving, deprived of their natural food sources.

For the new study, scientists hauled 50 milliliters (a handful) of seawater out of Boothbay Harbor in Maine, the home of the Bigelow Laboratory. They used a technique called fluorescence activated cell sorting to separate photosynthetic from non-photosynthetic (heterotrophic) cells and were surprised to find that picobilophytes lacked chlorophyll.

They sequenced the genomes of three picobilophytes and discovered in one of them, a new virus, whose circular genome they were able to reconstruct. They were also able to identify and sequence the DNA of creatures the picobilophytes had presumably eaten.

“There is a lot of uncharted biodiversity on our planet that we can’t get a hold of because we can’t cultivate the cells,” Bhattacharya says.

“Now, if you can reconstruct the nuclear genomes of individual cells in a sample of seawater, you can begin to infer not only the numbers and kinds of organisms that inhabit a particular ecosystem but also the functions of all the genes in their individual genomes.”

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