The Role of Microorganisms in the Ecosystem
This lab activity uses a controlled experiment to demonstrate different rates of decomposition for a variety of man-made and natural materials. Microorganisms are ubiquitous in the environment, where they have a variety of essential functions. Many microbes are uniquely adapted to specific environmental niches, such as those that inhabit the Dead Sea (Halobacterium), the bacteria and cyanobacteria that inhabit the boiling water springs in Yellowstone National Park, and Chlamydomonas nivalis, the algae that causes "pink snow." Microbes also play an essential role in the natural recycling of living materials. All naturally produced substances are biodegradable, which means that they can be broken down by living organisms, such as bacteria or fungi. Composting is an example of biodegradation that is easy to investigate the classroom. An examination of conditions that foster or impede composting gives insight to growth conditions of microorganisms as well as the proper function of the ecosystem.
Upon completion of this activity, the students will be able to:
- describe the steps used in a controlled experiment.
- identify the variables in this experiment.
- analyze the data by determining the rate of decomposition for each material.
- compare and contrast the nutritional requirements for microbes and humans.
Students should have prior knowledge of the concepts of landfills, compost piles, and bioremediation. This lesson will further investigate the concept of bioremediation, and how microbes can be beneficial in the maintenance of our environment.
bioremediation (the use of microorganisms to remove or detoxify undesired or toxic chemicals from the environment); bioaugmentation (the addition of necessary nutrients required to speed up the rate of degradation of a contaminant); xenobiotic compounds (compounds that are chemically synthesized and do not exist naturally); microbial plastic (a product produced by microbes that is an alternative to plastic, having similar qualities but is biodegradable)
Print a PDF of this activity
The Role of Microorganisms in the Ecosystem
ALL K-12 LESSON PLANS
|Microbes: Transformers of Matter and Material|
"Microbes can do anything they want, wherever they want -
without microbes, humans wouldn't be alive"
Introduction to Microbes:
The GOOD, the BAD, and the GLOBALLY POWERFUL
Throughout the history of time, bacteria have caused more human deaths on Earth than any other known cause, directly through the diseases of cholera, dysentery, meningitis, measles, pneumonia, scarlet fever, tuberculosis, and others. At the same time, the Good is that microbes provide many essential services to Earth, including allowing plant productivity (the dominant base of Earth's food web) to be sustainable, and allowing humans to live - basically, without microbes, humans wouldn't be alive. Finally, microbial organisms are collectively incredibly powerful at the global scale – 50% of the total oxygen produced over the history of the Earth is from bacteria; 75% of additions of nitrogen to the atmosphere, and 92% of removal from the atmosphere are due to bacteria. And of that nitrogen, bacteria produce 88% of the nitrous oxide released to the atmosphere, N2O, which is 300 times more potent than CO2 as a greenhouse gas. Microbes are also responsible for ~70% of the methane production on Earth (25x more potent than CO2), and ~50% of the CO2 put into the atmosphere comes from bacteria.
In this lecture we will learn about the diversity of microbes, how different microbes function to gain energy, and we will specifically learn about the "Good" aspects of microbes and the impacts of microbes on ecosystems and on our globe.
The Take Home Messages for this lecture are:
Microbes can do anything they want, wherever they want and Without microbes, humans wouldn't be alive.
DefinitionMicrobes are organisms that we need a microscope to see. The lower limit of our eye's resolution is about 0.1 to 0.2 mm or 100 - 200 um (microns). Most microbes range in size from about 0.2 um to the 200 um upper limit, although some fruiting bodies of fungi can become much larger. Microbes include the bacteria, algae, fungi, and protozoa. In this lecture we will discuss mostly the bacteria and the fungi.Definition: MicrobesMicrobes are organisms that we need a microscope to see. The lower limit of our eye's resolution is about 0.1 to 0.2 mm or 100 - 200 um. Most microbes range in size from about 0.2 um to the 200 um upper limit, although some fruiting bodies of fungi can become much larger (i.e., mushrooms). Microbes include the bacteria, algae, fungi, and protozoa. In this lecture we will discuss mostly the bacteria and the fungi.
EvolutionThere are two major groups of bacteria, the "eubacteria" and the relatively recently discovered "archaebacteria". The eubacteria contain most of the common bacteria such as E. coli (a common bacterium in the human gut) and the cyanobacteria (blue-green algae). The archaebacteria are found mainly in the deep ocean near hydrothermal vents. What is striking from the standpoint of the divergence of genetic material (the order and sequences of genes), is that these two groups of bacteria are more different than are animals and plants. In other words, these two groups of bacteria have evolutionarily diverged further from one another than animals have diverged from plants through evolutionary history.
Introduction to Some of the Important Microbes(A) Bacteria
Bacteria are found everywhere in water, soil, and even air. These small prokaryotic cells, typically from 0.2 to 1 um in length, are capable of living in boiling water, frozen ground, acid volcanoes, and at the bottom of the ocean (for a refresher on the different kinds of "cells", please click here ). They can reproduce by doubling with a generation time of 20 minutes, or survive for centuries in a resting stage. In natural waters (lakes, streams, oceans) their generation time is around 1 day. In soils they live in a film of water around plant roots or other particles, and their activity is dependent on the temperature and the amount of available moisture. In general, bacteria are found in concentrations of 106 cells/mL of water in surface waters, and 109 cells/mL of soil in soils and sediments.
Some bacteria are capable of locomotion, and they possess the only rotary motor known in all of biology. This motor, similar to a wheel and axle, is capable of spinning a flagellum at speeds of 100 revolutions per second, or 6,000 rpm. Bacteria can propel themselves at a rate of 10 times their body length each second (that would be like humans running at 20 meters/sec (45 mph or 72 km/hr), while the fastest humans now run at only about half that rate (28 mph or 44.7 km/hr; Usain Bolt, 2009).
Bacteria, like all cells, are composed mostly of carbon, oxygen, nitrogen, hydrogen, phosphorus, and sulfur in the following percentages:
|Bacteria take these elements and arrange them into polymers in the cells in the following percentages:|
52.4% protein (amino acids, CHNOS)
19.9% nucleic acid (organic bases, CNOHP)
16.6% polysaccharide (sugar, CHO)
9.4% phospholipid (C-16 acid + P, CHOP).
Note that the C:N:P element ratio of bacteria is more nutrient rich than the Redfield ratio for algae (C:N:P of algae = 106:16:1, and for bacteria = 106:19:6). in other words, for a given amount of carbon, bacteria have ~15% more nitrogen and 6 times more phosphorus. These ratios indicate that bacteria would need to degrade more C of plants to get the N and P that they need.
Fungi grow in the form of a finely-branched network of strands called hyphae, which are 5-10 um in diameter. These hyphae can release digestive enzymes and take up nutrients over their entire length. Fungi can absorb only small molecules such as sugars or peptides less than the size amino acids. The reproductive organs of the fungi are called fruiting bodies or sporangia (e.g., the aboveground structure of a mushroom), which are sacs or other tissues that contain the fungi spores.
Fungi are uncommon in aquatic environments. On land, the amount of hyphae in the soil is measured in hundreds or thousands of meters of length per gram of soil. For example, the total length of hyphae in a gram of soil (about the amount that would fit on the fingernail of your little finger) can reach up to 1,600 meters (think about that for a minute).
Fungi secrete enzymes that can break down cellulose into glucose, one of the few kinds of organisms able to do this. Fungi are the only known organisms that degrade lignin completely. Cellulose and lignin are structural materials in plants that are difficult to degrade. The fungi do not use the breakdown products of lignin, but instead they use hydrogen peroxide to oxidize lignin in place. The breakdown products diffuse away, exposing the cellulose to enzymatic attack.
Protozoans are single-celled eukaryotes, not photosynthetic, that move by flagella or cilia. In oceans and lakes, the small 2-10 um long flagellates are the most important predators on bacteria. The larger ciliates (e.g., Paramecium) prey mostly upon photosynthetic cyanobacteria and small eukaryotic algae. In some termites, anaerobic protozoans in the gut degrade cellulose.
4. How do Bacteria Gain Energy to Grow?Click here for background help on reduction-oxidation chemistry.
* Assimilative versus Dissimilative processes
Microbes must acquire certain elements to grow and reproduce -- these elements compose their protoplasm in the proportions listed in the table above. In addition, they must produce ATP in order to use the stored energy in this molecule to operate various cellular processes. Assimilative processes are used to bring needed elements into the cell and to incorporate them into the cell protoplasm. Dissimilative processes do not incorporate elements into the cell, but instead they use the energy gained in the process to form ATP.
Microorganisms are classified as autotrophs or heterotrophs based on whether or not they require pre-formed organic matter. Autotrophs derive energy from either light absorption (photoautotrophs) or oxidation of inorganic molecules (chemoautotrophs). In most of the light reactions the bacteria are fixing carbon dioxide into organic carbon, just as green plants do. Some photosynthetic bacteria (photoheterotrophs) require pre-formed organic matter as reducing agents, but generate ATP from the absorption of light energy. Finally, some bacteria and fungi (heterotrophs) used pre-formed organic matter as both a source of energy to generate ATP and as a source of carbon for the cell, just as animals do. The following table summarizes the classification of the ways in which microbes process energy.
|Classification||Energy source for generating ATP||Source of carbon for the cell||Example of organisms|
|Photoheterotroph||Light||CO2, organic matter||Bacteria|
|Heterotroph||Organic matter||Organic matter||Bacteria, fungi, animals|
As an example of the diversity of dissimilatory reactions that bacteria use to produce energy, consider the following table that shows various reduction-oxidation reactions (for a primer on "redox" reactions, please click here ). Note that all of these reactions listed below are performed by chemoautotrophs. A "+" in the table indicates that bacteria can use the pair of electron acceptor and donor to run a redox reaction that produces sufficient energy for growth. A "-" indicates that bacteria cannot use the redox pair for growth (this is not a table to memorize, but to illustrate the diversity of ways that bacteria can gain energy compared to how, e.g., humans gain energy - do you know which box in the table below represents how animals gain energy?). CHO is a shorthand for organic matter containing Carbon, Hydrogen, and Oxygen.