Bacteria Gang Up On Algae, Quashing Red Tide

Cells of the dinoflagellate Lingulodinium polyedrum, collected at seaduring a bloom in the summer of 2005, shows reddish areas signifyingnatural chlorophyll fluorescence, blue areas revealing DNA and green"dots" marking the cells of RCA cluster, bacteria implicated as a redtide killer. (Credit: Scripps Institution of Oceanography, UC SanDiego)ScienceDaily (May 6, 2008) - Researchers at Scripps Institution ofOceanography at UC San Diego have identified a potential "red tidekiller." Red tides and related phenomena in which microscopic algaeaccumulate rapidly in dense concentrations have been on the rise inrecent years, causing hundreds of millions of dollars in worldwidelosses to fisheries and beach tourism activities. Despite theirwide-ranging impacts, such phenomena, more broadly referred to as"harmful algal blooms," remain unpredictable in not only where theyappear, but how long they persist.New research at Scripps has identified a little-understood but commonmarine microbe as a red tide killer, and implicates the microbe in thetermination of a red tide in Southern California waters in the summer of2005.While not all algal outbreaks are harmful, some blooms carry toxins thathave been known to threaten marine ecosystems and even kill marinemammals, fish and birds.Using a series of new approaches, Scripps Oceanography's Xavier Mayaliinvestigated the inner workings of a bloom of dinoflagellates,single-celled plankton, known by the species name Lingulodiniumpolyedrum. The techniques revealed that so-called Roseobacter-CladeAffiliated ("RCA cluster") bacteria--several at a time--attackedindividual dinoflagellate by attaching directly to the plankton's cells,slowing their swimming speed and eventually killing them.Using DNA evidence, Mayali matched the identity of the RCA bacterium inrecords of algal blooms around the world.In fact, it turns out that RCA bacteria are present in temperate andpolar waters worldwide. Mayali's novel way of cultivating theseorganisms has now opened up a new world of inquiry to understand theecological roles of these organisms. The first outcome of thisachievement is the recognition of the bacterium's potential in killingred-tide organisms."It's possible that bacteria of this type play an important role interminating algal blooms and regulating algal bloom dynamics intemperate marine waters all over the world," said Mayali.The research study, which was coauthored by Scripps Professors PeterFranks and Farooq Azam, is published in the May 1 edition of the journalApplied and Environmental Microbiology."Our understanding of harmful algal blooms and red tides has been fairlyprimitive. For the most part we don't know how they start, for example,"said Franks, a professor of biological oceanography in the IntegrativeOceanography Division at Scripps. "From a practical point of view, ifthese RCA bacteria really do kill dinoflagellates and potentially otherharmful algae that form dense blooms, down the road there may be apossibility of using them to mitigate their harmful effects."The researchers based their results on experiments conducted withsamples of a red tide collected off the Scripps Pier in 2005. BecauseRCA bacteria will not grow under traditional laboratory methods, Mayalideveloped his own techniques for identifying and tracking RCA throughhighly delicate "micromanipulation" processes involving washing andtesting individual cells of Lingulodinium. He used molecular fluorescenttags to follow the bacteria's numbers, eventually matching its DNAsignature and sealing its identity."The work in the laboratory showed that the bacterium has to attachdirectly to the dinoflagellate to kill it," said Mayali, "and we foundsimilar dynamics in the natural bloom."Franks said he found it a bizarre concept of scale that Lingulodiniumdinoflagellates, which at 25 to 30 microns in diameter are known to swimthrough the ocean with long flagella, or appendages, are attacked bybacteria that are about one micron in size and can't swim."It's somewhat shocking to think of something like three chipmunksattaching themselves to an elephant and taking it down," said Franks.While the RCA cluster's role in the marine ecosystem is not known, Azam,a distinguished professor of marine microbiology in the Marine BiologyResearch Division at Scripps, said harmful algal blooms are an importantproblem and consideration must be given to the fact that red tidedinoflagellates don't exist in isolation of other parts of the marinefood web. Bacteria and other parts of the "microbial loop" feed on theorganic matter released by the dinoflagellates and in turn thedinoflagellates are known to feed on other cells (including bacteria)when their nutrients run out.Dinoflagellate interactions with highly abundant and genetically diversebacteria in the sea have the potential to both enhance and suppressbloom intensity--but this important subject is only beginning to beexplored."The newly identified role of RCA cluster is a good illustration of theneed to understand the multifarious mechanisms by which microbesinfluence the functioning of the marine ecosystems," Azam said."This type of discovery is helping us understand algal bloom dynamicsand the interactions among the components of planktonic ecosystems inways that we'd imagined but previously lacked evidence," said Franks.The National Oceanic and Atmospheric Administration's ECOHAB (Ecology ofHarmful Algal Blooms) program funded the research.Adapted from materials provided by University of California - San Diego,via EurekAlert!, a service of AAAS.Need to cite this story in your essay, paper, or report? Use one of thefollowing formats: University of California - San Diego (2008, May 6). Red Tide KillerIdentified: Bacteria Gang Up On Algae, Quashing Red Tide Blooms.ScienceDaily. Retrieved May 7, 2008, fromhttp://www.sciencedaily.com-/releases/2008/05/080501125429.htm