Microscopic algae have a unique relationship with corals in that they store excess nitrogen in crystal form and then feed it to corals as it is needed, according to a study published in the American Society of Microbiology’s mBio online open access journal. While scientists have been aware of the capability of microbes to store excess nitrogen, this study helps to understand the process in which microbes store nitrogen.
“It was a great surprise to find the nitrogen-rich crystals inside the algae,” corresponding author Anders Meibom of the École Polytechnique Fédérale de Lausanne, Switzerland said in a press release. “It all makes perfect sense now. The algae suck up the ammonium and nitrate like a sponge when the concentration of these molecules increases, then store this nitrogen as uric acid crystals for later use.”
The researchers studied cauliflower coral (Pocillopora damicornis) and exposed frags of the coral to varied concentrations of isotopically-labeled nitrogen-rich compounds. Cauliflower coral protects the photosynthethic algae (dinoflagellates), which provides the corals with sugars and nitrogen to survive. They used a new technique called nano-scale secondary ion mass-spectrometry (NanoSIMS) to follow where the nitrogen travels within the coral. The dinoflagellates don’t retain the nitrogen for long, translocating the nitrogen-rich compounds (ammonium, nitrate or aspartic acid ) to the coral host within six hours after exposure.
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According to the researchers, the process of translocating the nitrogen helps to determine how corals go through the roller coastal cycle of nitrogen concentrations. Meibom says that the coral-algae symbiosis is an efficient way to deal with the nitrogen fluctuations and availability. “When the nitrogen availability suddenly becomes high, the algae can take up large amounts of nitrogen on a timescale of a few hours, store it into crystals inside the algae cells and then release this stored nitrogen for metabolic processes and growth when the nitrogen levels become normal again,” Meibom said.