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03.2020 | THE SCIENTIST 15

Notebook

NEWS AND ANALYSIS

THIBAUT BRUNET, KING LAB

Rhodopsins on

Loan

A

few years ago, Alexandra Worden

was watching as an $800,

medical-grade fluorescence

activated single-cell sorter dangled

from a crane, about to be loaded onto

a research vessel—and hoping the crane

operator appreciated just how delicate

the equipment was. The marine micro-

bial ecologist and her colleagues were

about to set sail on the Atlantic Ocean

to collect unicellular eukaryotes and

sequester them individually for single-

cell whole-genome sequencing. The trip

was part of a survey that also included

expeditions on the Pacific Ocean to find

archaea, bacteria, and other organisms

associated with these microbes. Worden

and her collaborators wanted to avoid

bringing the seawater samples back to

the lab, which would risk distorting the

bio diversity of the sample—“some guys

just don’t make it,” says Worden, espe-

cially when it can take days to steam

back to shore. So instead, they’d decided

to bring the lab to the field.

With the crane operation well-

executed and the instrument safely on

board, the crew set off on its journey. The

researchers gathered seawater, fluores-

cently stained cells for a food vacuole to

label those organisms that were actively

eating, and fed samples to the cell sorter

to sift out the fluorescent cells from the

rest. The vast majority of cells selected

turned out to be choano flagellates, pred-

atory eukaryotes that feed on bacteria.

The team then began looking for bac-

teria and archaea among the choano-

flagellates, but in doing the sequencing to

identify prokaryote genomes, “we weren’t

getting a big signal,” says Worden, a pro-

fessor at GEOMAR, the Helmholtz Cen-

tre for Ocean Research in Kiel, Germany,

and a senior scientist at the Monterey Bay

Aquarium Research Institute (MBARI)

in California.

MARCH 2020

MARINE PREDATORS: Choanoflagellates

(pictured here in a multicellular state) are

eukaryotes that feed on bacteria in the ocean.