Picky protozoa may sense poison in prey.
When a person bites into horseradish, it bites back--producing a stinging sensation that deters many people from taking a second mouthful.
Activities like the chomping action of teeth destroy barriers inside a plant cell that keep certain enzymes and substrates separate. When mixed, these molecules produce chemicals that can protect the plant from being eaten by would-be predators.
Now, researchers report that single-celled organisms may defend themselves in a similar way.
Many types of marine algae algae (ăl`jē) [plural of Lat. alga=seaweed], a large and diverse group of primarily aquatic plantlike organisms. These organisms were previously classified as a primitive subkingdom of the plant kingdom, the thallophytes (plants that produce a substrate called dimethlysulfoniopropionate (DMSP), which is broken down chemically into dimethyl sulfide (DMS) and acrylate by an enzyme called DMSP lyase lyase /ly·ase/ (li´as) any of a class of enzymes that remove groups from their substrates (other than by hydrolysis or oxidation), leaving double bonds, or that conversely add groups to double bonds. . This DMS plays a major role in the global sulfur cycle, cloud formation, and possibly climate control. Acrylate is known to be poisonous to microorganisms.
Both DMSP and DMSP lyase reside within algal algal
pertaining to or caused by algae.
is very rare but systemic and udder infections are recorded. See protothecosis.
the algae Prototheca trispora and P. cells, but the chemical reaction doesn't take place unless a cell is injured--by a hungry predator, for example. Researchers can monitor the amount of algae ingested by a predator in the lab by measuring the amount of DMS that diffuses out of it.
Gordon V. Wolfe, a microbial ecologist at Oregon State University Oregon State University, at Corvallis; land-grant and state supported; coeducational; chartered 1858 as Corvallis College, opened 1865. In 1868 it was designated Oregon's land-grant agricultural college and was taken over completely by the state in 1885. in Corvallis, and his colleagues at the University of Bremen The University of Bremen (German Universität Bremen) is a university of approximately 23,500 people are currently studying, teaching, researching and working from 126 countries in Bremen, Germany. It was founded in 1971. in Germany have found that some protozoa which are sensitive to large amounts of DMSP lyase can survive on algae that make only small amounts of the enzyme. Even protozoa that eat high-enzyme-producing algae prefer the low producers, they report in the June 26 Nature. The researchers suggest that the potential for creating acrylate somehow deters predators.
"The idea that DMSP lyase is a grazing deterrent is really interesting," says Diane Stoecker, a biological oceanographer at the University of Maryland's Horn Point Environmental Laboratory in Cambridge, Md. "DMSP is produced in response to extreme environmental conditions, such as high salt concentrations, but a lot of algae that aren't exposed to extreme conditions produce it too. Until now, there hasn't been a good explanation."
When Wolfe's research team fed a protozoan protozoan (prō'təzō`ən), informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple , Oxyrrhis marina, a mixture of low- and high-DMSP lyase-producing algae, they detected little DMS for 24 hours Adv. 1. for 24 hours - without stopping; "she worked around the clock"
around the clock, round the clock . Then the amounts rose. Wolfe interprets this to mean that the protozoa consumed the low-enzyme producers before attacking the others.
"Oxyrrhis is the Tyrannosaurus Tyrannosaurus (tīrăn'ōsôr`əs, tĭr–) [Gr.,=tyrant lizard], member of a family, Tyrannosauridae, of bipedal carnivorous saurischian dinosaurs characterized by having strong hind limbs, a muscular tail, and short rex of marine protozoa," says Wolfe. "It's voracious. It'll eat almost anything. But even this nonfussy eater prefers food A over food B."
Wolfe cautions that he has not proved that the DMSP lyase reaction underlies the protozoan's food choice. The different algae strains are members of the same species, but they could differ in other ways besides lyase activity. The results do provide a solution to a previously troubling problem: Acrylate is toxic only at extremely high concentrations. Such concentrations, however, could be reached if algae were confined to the small digestive compartments within protozoa.
There are still "major gaps in our understanding," Wolfe said. He wonders how predators know in advance which strains of algae to avoid. The correct choice benefits the high-enzyme-producing algae because, unlike multicellular mul·ti·cel·lu·lar
Having or consisting of many cells.
multi·cel plants, which can sacrifice small amounts of tissue for the sake of the whole organism, single-celled creatures do not have any cells to spare.
The recent work also contributes to a growing appreciation that protozoa are more sophisticated than previously realized. "Unicellular unicellular /uni·cel·lu·lar/ (-sel´u-ler) made up of a single cell, as the bacteria.
Having or consisting of a single cell, as the protozoans; one-celled. organisms [like protozoa] are usually thought of as being simple, especially in terms of their behavior," says Peter G. Verity, an ecologist at the Skidaway Institute of Oceanography After the American Civil War (1861-1865), many of the plantations on the island were unable to continue without slave labor, and their owners gradually sold them to wealthy northerners, who mostly held them on speculation. in Savannah, Ga. "But unicellular does not necessarily equate with simplicity in terms of form or function."
"A lot of people are building computer models of marine microbial food webs," says Wolfe. "They assume that if a prey is present, a predator will eat it. The models need to be made more sophisticated."