A Teacher’s Guide to Stromatolite Explorer Investigation of a Microbial Mat Community Robin Bucaria, Dartmouth Middle School Dr. Brad Bebout, NASA Ames Research Center In this episode, the Stromatolite Explorer dives into a living microbial mat less than 5 millimeters thick. As the crew ventures deeper in the mat, the vehicle looses power and lacks solar radiation to recharge the battery. It is only through applying their knowl- edge of the daily cycles of the bacteria in the mat, that the crew is able to make it back to the surface. During the mission, the crew investigates the organ- isms that live in the mat and take chemical readings as they descend. The mission details life forms, biogeochemical cycles, and NASA’s interest in microbial mats. The Stromatolite Explorer video describes an imaginary voyage inside a microbial mat. This Teacherʼs guide contains a more detailed explanation of a number of the concepts discussed in the video, including the graphs presented in the video. Download the Stromatolite Explorer video from http://learn.arc.nasa.gov/microbe. Contents 1. Standards and Objectives 2. How to use the movie 3. Microbial mat organisms and structures 4. Microbial Mat Chemistry 5. Learning Activities 6. Glossary of Terms 7. Discussion Questions 8. Follow-up Activities 1. Standards and Objectives: National Education Standards: Fully Met Partially Met Addressed NSES C6(5-8): Regulation and NSES C4(5-8): Structure and NSES D6(5-8): Earth in the Solar Behavior a, b Function in Living Systems a, b System d NSES C7(5-8): Populations and NSES C6(5-8): Regulation and Ecosystems a, b, c Behavior c, d NSES D4(5-8): Structure of the Earth System h, k 2061: 5A(6-8) #1, #5 2061: 4E (6-8) #2, #4 2061: 5D(6-8) #2 2061: 5D(6-8) #2 2061: 5D(6-8) #1 2061: 5D(6-8) #1 2061: 5E(6-8) #2 2061: 5E(6-8) #1, #3 1 California Science Standards: Fully Met Partially Met Addressed Grade 6: Ecology #5: a, b Grade 6: Ecology #5: c Grade 7: Cell Biology #1: a Grade 7: Earth & Life History #4 a Grade 8: Chemistry of Living Systems #6 Objectives: At the end of the movie and discussion, the student will: 1. understand that a microbial mat is composed of layers of different microbes. 2. understand that these biological communities have been around over 3 billion years and contain some of the earliest forms of life. 3. learn that diatoms convert sunlight and carbon dioxide into fuel molecules and oxygen through the process of photosynthesis. 4. learn that cyanobacteria are singled celled organisms without an enclosed nucleus that also conduct oxygenic photosynthesis. 5. learn that other forms of bacteria, such as purple sulfur bacteria, conduct photosynthesis that doesnʼt produce oxygen: anoxygenic photosynthesis. 6. know that a microbial mat is a self sustaining ecosystem where one member of the community produces a gas or sugar that another member of the community needs to obtain energy. 7. discover that the chemical concentrations of oxygen and other substances change within the layers of the mat (a chemical gradient) due to the amount of light at that level, the1. community of producers at that layer, and the raw materials (sugar, chemicals, and gases), available at that level. 8. learn how NASA uses information about microbial mats to fi nd life on other worlds. 2. How to Use the Movie 1. Introduce mat organisms and biological structures using the material in this guide. 2. Introduce vocabulary from the Glossary of Terms included in this guide. 3. Select learning activities to use either before or after the viewing the movie. 4. Play the Stromatolite Explorer movie through once uninterrupted for the students to gain an overview of a microbial mat. 5. Play the Stromatolite Explorer movie again, stopping the fi lm and making explanatory comments. Transparencies of the annotated graphs can be made to use with the class. 6. Discuss the fi lm using the questions for discussion included in this guide. 7. Complete desired follow up activities listed in this guide that are available at http://learn.arc.nasa.gov/microbe 2 3. Microbial Mat Organisms and Structures: What are Microbial Mats? Have you ever and other members of the mat community. On the next fl oor, noticed green other microbes take the sugar and other byproducts for their spongy areas by food. By borrowing that “cup of sugar” from the microbes on water fountains, the fl oor above, they gain the energy they need and produce drain spouts or another form of that sugar for the surrounding microbes, gutters? The which in turn, use these materials and produce yet another green areas form of sugar for other microbes. The chemicals, gasses where water col- and sugars that one microbe does not need may be used by lects are biofi lms another microbe within the community. created by bac- teria. Allow the What are Diatoms? bacteria in those biofi lms to grow for longer periods of time and a microbial mat Diatoms are one-celled algae with a covering, known as a will form. A microbial mat is composed of layers of different frustule, of silica (or glass) that makes up their cell wall. Dia- microbes, working together in a self-sustaining ecosystem. toms are eukaryotic; Color, smell and location help to identify microbial mats. The they have a mem- top layer of a mat often contains blue green algae, or cyano- brane-bound nucleus. bacteria, as well as diatoms. White, purple, and black appear Notice the nucleus, can appear in the lower layers of a mat. Because they are chloroplasts and other attractive as food for animals, mats live in areas that are least separate organelles 1. attractive to other forms of life. Hot areas, salty areas, dry ar- inside the cell wall. eas, cold areas and places that are sheltered from animal for- Diatoms are autotrophs agers are the locations where microbial mats grow. It wasnʼt and manufacture their always that way. Before grazing animals appeared on Earth, own food using the sunʼs energy and water in a process about 500 million years ago, microbial mats were far more called photosynthesis. common, even dominated the biosphere of the early Earth. What are Cyanobacteria? A microbial mat is a complex food web. Like all other life Cyanobacteria is the name giving to a group of bacteria that forms, each member of this food web requires energy. For perform oxygen producing photosynthesis. All cyanobacteria photosynthetic microbial mats, energy enters the upper layers are unicellular but some grow in colonies or fi laments, often of the ecosystem as light, which is captured by the cyanobac- surrounded by a gelatinous sheath. Cyanobacteria, as with teria and diatoms with photosynthesis. Other microbes living other bacteria, are prokaryotes. Their genetic material is not in this ecosystem sustain life by using the gases, sugars, and contained in a nucleus in the cell. While cyanobacteria were organic matter produced in these upper layers to gain energy. once mistaken for algae, they are actually prokaryotic organ- Each member of the community produces something that isms (they have no membrane –bound nucleus). Through allows another member of the community to extract energy the process of photosynthesis, cyanobacteria changed from the environment. Think of it this way: A microbial mat is Earthʼs early atmosphere, creating the oxygen rich environ- like an apartment building, with different microorganisms living ment we know today. Cyanobacteria fossils have been found on different fl oors of the building. In the penthouse suit, clos- that are more that 3.5 billion years old. est to the sun, are the cyanobacteria. They take the carbon dioxide and produce oxygen and sugars used by themselves 3 Microcoleus is a fi lamentus cyanobacteria that produces What are Sulfate Reducing Bacteria? food through the process Sulfate reducing bacteria of photosynthesis. In the reduce sulfate to hydrogen picture at right, it can be sulfi de. They are bacteria seen that many Microcoleus that use sulfate as an elec- trichomes are enclosed in tron acceptor (see respira- tion) to derive energy from a common sheath, giving organic matter. They are generally classifi ed as anaerobes rise to a very characteristic because most SRB cannot exist where oxygen is present. “bundle” appearance. Mi- crocoleus is very common in microbial mats from hypersaline environments, and in soils. What are Colorless Sulfur Bacteria? Colorless sulfur bac- teria use hydrogen Oscillatoria is a type of fi lamentous cyanobacteria with taper- sulfi de and oxygen ing, unbranched fi laments as a kind of battery (trichomes), often with a to synthesize sugars. rounded cell. Oscillatoria Because the place glide by wave movements where they can get Oscillatoria of tiny fi bers. can both oxygen and hydrogen sulfi de moves on a daily cycle, be found in salt marshes, they must migrate, too. hot springs, in damp soil, in fresh water and in the sea. What else lives in the mat? Various protists and other organisms can live in Gloecapsa is a unicellular the mat. In the movie, a nematode wiggles through the mat. cyano-bacteria that have groups of cells held together by a muscilaginous sheath. Nematode A nematode is a worm that lives in soil, water or in plants or animals. What are Purple Sulfur Bacteria? Nematods can be Purple sulfur bacteria use less than a millimeter infrared radiation and hy- in length and range drogen sulfi de (the rotten to several meters in egg smell found in swamps, length. sulfur springs or stagnant water) to perform anoxygen- ic photosynthesis, a kind of photosynthesis that doesnʼt produce oxygen.