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Of Slime and Seawater

Malfatti, a marine biology Ph.D. student at Scripps Oceanography, is using an atomic force microscope to examine the interactions between single-cell bacteria and even smaller particles known as marine microgels. Marine microgels were discovered only as recently as the 1990s. Scientists now believe that 10 percent of all dissolved organic matter in marine waters is microgel.

Marine bacteria play an important role in the ocean carbon cycle, interacting with all organic matter present in seawater. Gels are the smallest particles in the ocean and very abundant at 100 million parts per milliliter. This produces considerable interaction with the 1 million bacteria that also exist in the same milliliter of seawater. That interaction might be different than normal in the northern Adriatic where mucilage forms, according to Malfatti.

“Human impact may be part of the equation,” Malfatti said. “But the mucus formation has to be studied across a range of scales, from the microscopic scale where bacteria interact with gels to the mesoscale where water circulation, seawater temperature, and wind impact the carbon cycle in the northern Adriatic basin.”

Recurring mucilage phenomena are nothing new to the northern Adriatic, where the slime was first recorded in 1729. But major events in recent decades threatened to drive away tourists from Adriatic beaches. Mucilage also harms the fishing industry because it befouls nets.

Malfatti's advisor, Farooq Azam, a distinguished professor in the Marine Biology Research Division at Scripps Oceanography, emphasizes that there is nothing terribly unusual about microgels in the sea. All areas of the sea have them. All organisms produce mucus as part of their survival strategies, such as for protection from microbial attack or to capture food. Some organisms such as algae and bacteria release mucus into the environment in large amounts, and many microbes also degrade and use it for their nutrition. So, there is a dynamic pool of mucus and microgels everywhere in the ocean.

Mucilage events are not the same as microalgae blooms, which are caused by excessive nutrients in seawater, usually from agricultural runoff. Instead, Malfatti believes that precursors of mucilage exist for almost the entire year in the northern Adriatic. On some occasions during warmer months, gels start to aggregate in massive amounts and rise to the surface. According to Malfatti's research, bacteria might dictate the rate that microgels coalesce, forming the massive mucus clouds that rise and linger on the surface until they are broken up by wind and storms, and then decay and sink. Malfatti hypothesizes that in the northern Adriatic, bacteria enzymatically modify the surface of the microgels, changing their degree of stickiness. This would lead to the formation of bigger aggregates of gels, transforming into mucilage.

“It is critical to understand the role of the bacteria in shaping the organic matter in the sea at the microscale level to better predict mucilage events,” she said.

Next page: Using a force like no other

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