Magazine article Oceanus

A Green Thumb for Synechococcus: Growing Marine Bacteria in the Laboratory Is a Challenge

Magazine article Oceanus

A Green Thumb for Synechococcus: Growing Marine Bacteria in the Laboratory Is a Challenge

Article excerpt

Anyone who has tried to grow orchids or keep a bonsai tree alive will tell you that cultivating plants is not always simple. My thesis research absolutely depended on cultivating certain types of "plants" and keeping them alive, so that I could investigate the factors that boost or thwart their ability to grow.

My specimens were among the most ubiquitous organisms on Earth and critical to supporting life on our planet. Yet we know surprisingly little about them. That's because it's so difficult to observe them in their natural habitat--the ocean.

To make some headway into learning what allows them to grow, reproduce, and survive in the ocean, ironically we needed to be able to grow them in the laboratory. And that's just a very different environment from what they encounter in nature.

My specimens are remarkably abundant and are found across the world's oceans. Yet no one even knew they existed until they were discovered in 1979 by scientists at Woods Hole Oceanographic Institution (WHOI): Stanley Watson, John Waterbury, and Freddy Valois.

They are called Synechococcus, and they aren't plants, but rather single-cell bacteria. Though they are leafless, rootless, and adrift in the sea, they use the same machinery as terrestrial plants--photosynthesis--for the same end: to convert carbon dioxide into organic building blocks. Collectively they move mammoth amounts of carbon around the planet. They take about 20 percent of the carbon dioxide drawn from the air into coastal waters and transform it into biomass--creating a critical source of food at the base of the marine food chain. In the process, they also release a significant portion of the oxygen we breathe.

Unexplored population dynamics

The ocean is filled with photosynthetic plankton more numerous and varied than any fields or forests of terrestrial plants. But these vital ecosystems remain largely unexplored because of limited access and observational tools.

In 2003, my Ph.D. co-advisor, WHOI biologist Heidi Sosik, began using a new automated underwater instrument that she co-invented with WHOI scientist Rob Olson. The instrument, called FlowCytobot, detects and records small phytoplankton. Plugged into a seafloor node, it receives power via an undersea cable from WHOI's Martha's Vineyard Coastal Observatory. It transmits back to shore hourly observations of microscopic plankton off the coast of Martha's Vineyard.

Over the past twelve years, FlowCytobot has revealed complex patterns of Synechococcus abundance. To understand some of these patterns, we needed information about the different types of Synechococcus that could make up the population. While FlowCytobot can detect Synechococcus, it cannot distinguish among different types. So we analyzed genetic material in seawater samples and identified five main types of Synechococcus off Martha's Vineyard. Interestingly, these different types were more or less abundant at different times of year.

Obvious questions arose: Why are certain Synechococcus more abundant during some seasons than at other times? Even though they are all in the same genus, do different types of Synechococcus have different responses to different water temperatures, light, nutrients, or other environmental factors?

To answer these questions, we needed to conduct experiments on the different types of Synechococcus. To do that, we needed to maintain populations of them in the lab, which scientists refer to as "cultures." My challenge was to find the right laboratory conditions that would enable the growth of the five main types of Synechococcus. As I found out, just as each type of plant has specific needs--for sun, soil, moisture, and fertilizer, for example--so do bacteria.

Master gardeners

Figuring out the exact requirements or conditions that allow bacteria to thrive in the lab can be a less-than-straightforward process. Being new to culturing Synechococcus, I was fortunate enough to be able to seek guidance on how to isolate different types of Synechococcus into culture from the pioneers, John Waterbury and Freddy Valois, still working here at WHOI. …

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