Part 4: Amensalism Introduction Production of antibiotics by microorganisms can be used as an example of another microbial interaction called amensalism. Amensalism is when one species in an environment impedes the success of another species, but is not directly benefitting by the interaction. Certain fungi and bacteria produce antimicrobial substances prior to sporulating. Formation of both bacterial endospores and fungal reproductive spores are energy consuming pathways. Species in genera like Penicillium, Bacillus and Streptomyces will produce antibiotics naturally to help reserve nutrient sources to aid in completion of spore formation. Sensitive organisms that are nearby would be inhibited or killed by the chemical compound. It is important to note that other nonspore forming organisms may also produce antimicrobial substances and thus could also be found in relationships described as amensalistic. In this exercise we will determine if any of the four bacterial species are sensitive to the polymyxin antibiotics produced by the spore forming bacterium Bacillus polymyxa Procedure 12.4 NOTE This procedure will be performed by one group. Your instructor will assign this group. ONE STUDENT GROUP 1. Obtain and label a YEG plate with a single streak of B. polymyxa. 2. Using Figure 12.2 as a guide, inoculate each organism in a single streak starting at the outer edge of the plate moving toward the center streak. Make sure to get as close as possible without touching the B. polymyxa. 3. Invert the plate and place in your group bin. Bins will be incubated at 37 C for 24 hours. Return all stock cultures to your instructor. E coll S.aureus P.vulgaris 8 polymyx bluedoor, LLC Figure 12.2: YEG plate inoculated with a single streak of B. polymyxa. Four test organisms will be streaked from the outer edge towards the center. ( Part 4: Amensalism. Procedure 1. Analyze the YEG plate for growth of each test organism and the relative effects of the polymyxin produced by the B. polymyxa. 2. In the diagram below shade in the area of growth for each organism and denote the area of inhibition (if one is present). 3. Using a ruler measure the length of the growth along the streak and compare that to the total length of the streak. The difference represents the zone of inhibition measurement. Record your results below. 4. Dispose of your plate in the biohazard bin. Results and Observations E.col Saun 4 Pvulgaris subtil 8 polymyx List the zone of inhibition measurements for each test organism: S. aureus: B. subtilis: E. coli: P. vulgaris: Question 1. Which organisms when combined would be examples of amensalism? obluedoor LLC Farcise 12 | Microbial Interactions 183 Part 4: Amensalism Be sure to have read the introduction for part 4 as well as Procedure 12.4 on page 178. Read through the introduction and procedure for the analysis of part 4 on page 183. Observe the image below and record your data in the "Results and Observations" section. Remember the zone of inhibition refers to the area where the organism does not grow. If growth is observed along the entire streak line this means there is no zone of inhibition. You must shade in the area of growth in the diagram in this section as well as list the zone of inhibition measurements in millimeters (mm) for each test organism. After recording all data for part 4 answer question 1 at the bottom of page 183. For results use a ruler with mm measurements (or a cm ruler with mm divisions) and view the file at 100% magnification for measurement purposes. Stads millimeters (mm) for each test organism. After recording all data for part 4 answer question 1 at the bottom of page 183. For results use a ruler with mm measurements (or a cm ruler with mm divisions) and view the file at 100% magnification for measurement purposes. Enceli P. voly B.sub