Bacteria represent an amazingly diverse group of organisms that are of great ecological, economic, agricultural, and medical importance. Cyanobacteria, also known as blue-green bacteria, contain thylakoid membranes with photosynthetic pigments (chlorophyll a and phycobilins) and are capable to oxygenic photosynthesis. Purple bacteria and green sulfur bacteria occupy habitats in the presence of hydrogen sulfide and oxidize and release sulfur gas rather than oxygen. Nitrogen fixing and denitrifying bacteria have an exceptionally important role in nitrogen cycling in terrestrial plant communities. Many vascular plants such as legumes and an aquatic fern have a symbiotic relationship with nitrogen fixing bacteria. Bacteria are also important carbon recyclers in the environment by assisting in the decomposition of dead organisms.
Bacteria are considered Prokaryotes (before the nucleus) and represent a lineage that is ancient and possess a number of novel features. Bacteria generally lack internal compartmentalized organelles that are bound by membranes. Organelles such as Golgi bodies (dictyosomes), chloroplasts, mitochondria, and nuclei are regarded as unique to Eukaryotic (true nucleus) organisms. Recently, evolutionary biologists have determined that two major kingdoms of bacteria are present on the planet. Eubacteria represent the true bacteria and contain many of the groups that we are most familiar with such as cyanobacteria. E. coli, Streptococcus, and Rhizobium. Archaebacteria represent an ancient lineage whose members occupy rather inhospitable habitats such as deep sea thermal vents and miles deep in the Earth=s crust, but are also found in more normal environments.
The objective of this lab is to examine the morphology, structure, and ecology of bacteria and cyanobacteria.
Activity 1. Bacterial Forms
A prepared slide of three bacterial forms is provided in the laboratory. Examine the slide by holding it up to the light to identify the three pink stained regions of the slide. Each region possesses a different form of bacteria. You will need to start with the 10X objective to identify these regions and then proceed to the 20X and 40X objectives.
6. In the space below, draw a representative of the three bacterial forms and provide dimensional measurements. You will probably need to review the use of the ocular micrometer from the lab on microscopes and cells.
Cocci (sphere-shaped) Bacilli (rod-shaped) width (µm) width (µm) Length (µm) length (µm)
Spirilli (spiral-shaped) width µm length µm
103 Comparison of surface area. Using data from the Microscope and Cell Lab, calculate the side surface area of an elodea leaf cell. Calculate a corresponding cell surface area for one bacillus bacterium.
Elodea leaf cell Width = μm
Length = μm
Area = width X length = μm2
Bacillus bacterium Width = μm
Length = μm
Area = width X length = μm2
How many bacteria would cover the surface area of one elodea leaf cell?
If an elodea leaf contained 2000 cells on one surface of the leaf, then how many bacteria could cover the entire leaf?
Activity 2. Cyanobacteria (Blue-green bacteria)
104 This group of ancient bacteria may represent the first organisms to produce atmospheric oxygen on Earth. Although they are prokaryotic, cyanobacteria do possess thylakoids and perform oxygenic photosynthesis. They are found in a wide variety of habitats from hot thermal springs at Yellowstone National Park to frigid lakes of Antarctica. Some forms of cyanobacteria grow in the fur of Polar Bears and actually tint the fur green. In central New York, cyanobacteria are common in stagnant water and soil.
Cyanobacteria are capable of binding calcium carbonate in unique dome-like deposits called stromatolites. These structures are common in tidal flats of Western Australia. Because they grow slowly and form distinct layers, some stromatolites have been aged to 3-3.5 billion years old.
Many species of cyanobacteria are nitrogen fixers like Rhizobium and Azotobacter. Nitrogen fixation occurs in specialized cells with thick cells walls called heterocysts. Nitrogen fixation by the cyanobacterium Anabaena is economically important.
You will be presented with several representatives of cyanobacteria. These may include Gleocapsa, Oscillatoria, Spirulina, and Anabaena. Make a wet mount and observe under high power on the light microscope. For each species, please draw the form of the colony; observe the presence/absence of heterocysts, the presence/absence of a protective gelatinous sheath, and the size of individual cells.
Gleocapsa
Oscillatoria
Spirulina
Anabaena
105