Unit Three Single-celled Organisms Michelle Wood Associate Professor Department of Biology University of Oregon Ph.D. in Zoology University of Georgia Michelle attended the University of Corpus Christi where she earned B.A. degrees in Biology and Speech. After graduating from the University of Georgia with a Ph.D., she continued her work as a postdoctoral student at the University of Chicago. She studied genetics and the evolutionary ecology of recently discovered photosynthetic organisms. After her postdoc, she continued as part of the research faculty in Ecology and Evolution Department until 1990. She then moved to the University of Oregon where she is now an Associate Professor. Dr. Wood’s research interests include studying picocyanobacteria from an evolutionary viewpoint. She is looking at how these microorganisms can survive in a wide range of marine environments. For instance, in the Arabian Sea, she and her student, Nelson Sherry, found that these organisms could reproduce several times a day and reach population sizes of more than a million cells per milliliter. These were free-living picocyanobacteria that bloomed during the summer Monsoon season. In the winter she found many examples of picocyanobacteria living symbiotically with dinoflagellates. She would like the students to know that people who study the ocean are a community of creative, curious, and wonderful people. She says, “If you are a student interested in ocean science, rest assured that there are many wonderful people out here who want to help you follow your dreams.” ©Project Oceanography 75 Spring 2002 Unit Three Single-celled Organisms Unit III Single-celled Organisms On the cutting edge… Dr. Wood at the University of Oregon is on the edge of scientific discovery as she explores some of the microscopic inhabitants of the marine environment. She is studying the relationship between a cyanobacteria and a dinoflagellate. She is interested in learning more about how these organisms create a symbiotic relationship that helps them succeed in nutrient-poor tropical waters. Introduction to Single-celled Organisms Lesson Objectives: Students will be able to do the following: • Compare and contrast three types of symbiotic relationships • Describe the relationship between zooxanthellae and coral • Explain the effects of nitrogen-fixing bacteria on their symbiotic partners Key concepts: symbiosis, commensalism, parasitism, mutualism, dinoflagellate, nitrogen-fixing cyanobacteria Symbiotic Relationships The word camouflaged from predators and symbiosis in its protected with the sea anemones’ simpliest terms tentacles while the anemones are means “living carried to various locations where together”. This food gathering is easier. The bobtail word describes a squid harbors light emitting bacteria. partnership These bacteria help create light between two patterns that camouflage the squid different kinds of organisms such as during hours of feeding. a sea anemone and a hermit crab or a squid and a bacterium. These Symbiotic relationships are long-term relationships associations that are usually can be divided advantageous to at least one into three broad member of the partnership. These categories: symbiotic relationships often occur commensalism, parasitism, and because of the nutritional needs of mutualism. These categories the members. There are many describe how each partner benefits examples of symbiosis to be found in from the relationship. In nature. For example, some hermit commensalism, one member crabs have shells covered with sea benefits while the other is neither anemones. The crab is helped nor harmed. A good example ©Project Oceanography 76 Spring 2002 Unit Three Single-celled Organisms of this type of relationship is the cleaned and the shrimp gets a free remora that can attach itself to a meal. shark. The remora gets a Symbiotic relationships occur free ride and between organisms of all sizes in all eats the scraps environments. Some partners are left by the shark. vastly different in size as evidenced It does not harm by the whale and its special barnacle or help the partner that lives in its skin. Some shark. In symbiotic partners are similar in size parasitism, one member is helped like the hermit crab and the sea while the other member is harmed. anemone. We often think of An example of a parasitic symbiotic relationships that include relationship is a tapeworm in a organisms that we can see without human. The parasite, the tapeworm, using a microscope, but symbiosis lives inside the human or host. The occurs in the micro-world as well. parasite is helped, because it gets Some microorganisms such as nutrition from the food in the diatoms with their glasslike outer human’s intestine. The human can coverings, dinoflagellates with their slowly starve, because the tapeworm whiplike projections, and even the is using the nutrition from the food tiniest bacteria are involved in the human eats. In mutualism, both symbiotic relationships. Some of organisms benefit as in the case of these relationships involve only the fish and the microorganisms while others can cleaner shrimp. include much larger animals. We will The fish enters a take a closer look at an example of “cleaning station” mutualism between a dinoflagellate where the shrimp removes parasites and a much larger animal that lives from the fish’s body. The fish gets in the marine environment. Dinoflagellate/Coral Symbiosis Dinoflagellates are common whiplike projections that are used for members of the phytoplankton found locomotion. Most of these organisms in the ocean. There are nearly 2000 are covered with species of these single-celled armored plates organisms that have been identified. called thecal They come in a variety of sizes but plates. Scientists are considered the mid-sized use these plates members of the micro world. They to help classify are generally smaller than the these organisms. diatoms and larger than the Dinoflagellates photosynthetic bacteria. also have different lifestyles. Some Dinoflagellates derive their name of them are photosynthetic, from their two distinct flagella or producing their own food, while ©Project Oceanography 77 Spring 2002 Unit Three Single-celled Organisms others must find food. A good support the coral animal. This example of a symbiotic relationship skeleton becomes a coral reef. The involving a photosynthetic oxygen released during dinoflagellate is the partnership photosynthesis is used by the coral between a zooxanthellae and a for respiration. Carbon dioxide coral. Corals are animals that are released during the coral’s related to sea respiration is used by the anemones and zooxanthellae during photosynthesis. form the huge The corals also produce waste geologically products such as ammonium. Some important coral of these products are used as reefs. nutrients by the zooxanthellae. “Zooxanthellae” are a type of dinoflagellate that specializes in As you can see both living symbiotically within the tissues organisms benefit from this of animals. In this mutualistic relationship, but they relationship, the zooxanthellae live must also give up inside the coral. The zooxanthellae is something. The called an endosymbiont and the dinoflagellate gives up coral is the host. These two partners some of its photosynthetic recycle the waste products from energy to the coral. In return the living processes to continue their coral must use a portion of that relationship. The endosymbiont uses energy to keep its surface clean and energy from the sun to grow branched colonies. This power the process of provides the dinoflagellate with photosynthesis. The adequate sunlight for zooxanthellae produces photosynthesis. The zooxanthellae’s sugar from carbon light requirements also restrict the dioxide in the water coral to depths at which the coral and releases oxygen. can grow. Why would organisms The food or sugar produced by this enter into a relationship where they process gives the coral energy. The had to give up something? In this presence of the zooxanthellae also instance, coral reefs are found in helps the coral produce calcium nutrient-poor waters, so this carbonate. This material is used to relationship provides both members build a cup-shaped skeleton to with sufficient nutrition. Cyanobacteria We are going to take a closer look at their color and because they also some very small members of the photosynthesize. These organisms microscopic world, because they are are not algae but rather a special important in symbiotic relationships. kind of bacteria. These bacteria are The cyanobacteria are sometimes unicellular, but they may combine to called “blue-green algae” because of form colonies or filaments. Some of ©Project Oceanography 78 Spring 2002 Unit Three Single-celled Organisms these colonies are large enough to developed symbiotic relationships be seen without a microscope. with a microbe that can fix nitrogen. Typical cyanobacteria get their color from a bluish These relationships between a pigment called nitrogen-fixer and a plant partner can phycocyanin. Many be found in all types of environments marine from forested areas to open ocean cyanobacteria waters. Some plants will even create contain an additional, special homes for these bacteria pink pigment called within their roots or stems in return phycoerythrin. These pigments are for the nitrogen they produce. In used by the cyanobacteria to capture exchange, the plant provides the sunlight during photosynthesis just bacteria with some of the energy as most plants use the chlorophyll