Microbial Safari: Isolation & Characterization of Unknowns in an Introductory Microbiology Laboratory

Abstract

Our undergraduate microbiology course serves about 100 students majoring in biology, nursing, chemistry, forestry and agriculture each semester. The course covers the morphology, physiology, genetics and classification of microorganisms. All students are required to take an accompanying laboratory that emphasizes standard procedures outlined in a published laboratory manual (Cappucino & Sherman 1999). Although this approach exposes students to different laboratory concepts and techniques regarding microorganisms, many students finish the course without understanding the practical applications of these techniques. Several microbiology educators have reported on new, innovative approaches that emphasize practical applications of standard microbiology lab procedures (Adamo & Gealt 1996; Blair & Bowen 1996; Fox 1997). Deutch (1994) recently proposed an investigative laboratory sequence based on the isolation and characterization of soil bacteria. Students suspended soil in nutrient broth and isolated individual microbes by streaking on agar plates. Each student then isolated an individual bacterium that he/she characterized for the rest of the semester. These characterizations were conducted using basic techniques from a standard laboratory manual. We have recently developed and tested an improved approach that emphasizes critical thinking and experimental design. Working in four-member teams, students in our microbiology course planned and carried out experiments to isolate and characterize a bacterial isolate from a specific habitat at our university. Once they isolated their own organism, they adopted this bacterium and characterized it for the rest of the semester. We built upon the work of Deutch (1994) and others in several ways. First, instead of instructing students how to isolate microorganisms from a particular habitat, we assigned them to teams who devised their own protocol to obtain single colony isolates. Initially, most teams were not successful, which in turn led to discussions on how one could reduce microbial numbers so that individual colonies could be isolated. Second, the extensive data gathered for each bacterial isolate was used to teach the students how to use references such as Bergey's Manual of Systematic Bacteriology (Holt & Krieg 1984; Sneath, Mair & Sharpe 1986) to classify their isolate. Third, we used a variety of different habitats from which to isolate organisms rather than one type of habitat, such as soil. This helped the students appreciate the ubiquity of microorganisms in the environment. Finally, each team concentrated upon a particular habitat to isolate their bacteria. This approach helped them make the connection between the physicochemical conditions of each habitat and the microorganisms present and consequently isolated by the students. This assignment accomplished the following: