[Example of a “Good” Report]

Microbial Scavenger Hunt


There exists an unseen realm of life hidden in our everyday reality. Our limited sight prevents us from seeing the diversity of microbial life that exists all around us. It can only be appreciated when examined on a microscopic level. This invisible lifeforms that elude our attention live on inanimate objects, often-harsh conditions, and sometimes in places we wouldn’t imagine life thriving. When given an opportunity some of the numerous places such life exists, it is possible to gain a glimpse of what is frequently missed everyday. The purpose of this experiment was to select particular natural environments in hopes of finding and isolating certain species of bacteria. Nearly all natural environments contain mixed populations of microbes. In order to study a microbe of interest, it is necessary to isolate and grow vast numbers of them in order to produce pure cultures. In order to isolate a particular microbe, it becomes necessary to incubate the sample under conditions that is favorable only for its growth. Such enrichment cultures are selective, and restrict the growth of many organisms and favor the one trying to be isolated. This reduces the confusion and difficulty in having to “sift” through and distinguish between the numerous colonies that can exist on a growth environment. Such techniques ensure that the microbe of interest is grown free from other bacteria species. Through streaking methods, and colony selection, isolation can be attained. Such isolated cultures can then be tested for morphology, motility, etc. For this experiment, the target bacteria species tested for included Thermophile, Actinomycete, Agar Decomposer, Azobacter, Bacillus fastidiuos, and Extreme Halophile. The various natural environments and procedures for their isolation will be explained and diagramed in the following section.

[Comment: perfect intro]

Materials and Methods:

*Please refer to pages 55-59 of the Fundamentals of Microbiology Laboratory Manual, printed by the University of Connecticut Department of Molecular and Cell Biology.

* For each of the organisms targeted and isolated, please note the appropriate protocol changes listed below:
Thermophile: 1. A small amount of soil taken from on campus was used.
  1. After the second enrichment broth was incubated at 55 degrees Celsius, and streaked onto the initial Nutrient Agar plate, three restreaks were done until the pure culture was obtained.
  2. In addition to growing the culture at 55 degrees, it was also grown at 25 degrees and 32 degrees Celsius.
Actinomycete: 1. After the enrichment culture was streaked onto the initial GLA
plate, three additional T-streaks were done in order to isolate a pure culture.
Agar Decomposer: 1. A small piece of seaweed taken from Long Island sound was
used as the source of bacteria.
  1. After the initial enrichment culture was streaked, 6 additional T-streaks were carried out in order to isolate a pure culture.
Azobacter: 1. After streaking the initial enrichment culture, four additional T- streaks were carried out in order to obtain a pure sample.
Baccillus fastidiosus: 1. After streaking the initial enrichment culture, four
additional T-streaks were done in order to gain pure culture. (For both mediums).
  1. In addition to the uric medium the culture was grown on, a Nutrient Agar medium was also used in order to observe growth.
Extreme Halophile: 1. There was no additional T-streaks carried out after the initial. (No growth occurred).

Data/Results: For the most part, this experiment was successful. The results for each species varied, but all were conclusive. Below is listed the results for each species:
Thermophile: For this species, the enrichment culture had the most growth. The initial streak also produced the most noticeable colony numbers, while the three subsequent restreaks, produced less and less colonies, until a pure culture was obtained. Upon testing, the bacterium appeared to have a Gram + Cocci morphology, but this was unexpected as most Thermophiles are Gram + Rods. Upon further examination of the gram stain, the presence of endospores was detected. Growth appeared to be greatest at the temperatures of 32 and 55 degress Celsius. No growth occurred at 25 degrees. [Celsius]

Actinomycete: The amount of growth of the enrichment culture and initial streak were fairly high in comparison to the later four restreaks. A gram stain revealed that the species had a gram + cocci morphology and the presence of endospores [They were not endospores just spores] were detected.

Agar Decomposer: Again, most growth occurred during the enrichment culture and initial T-streak. The amounts of noticeable colonies were less and less on the six later restreaks, until the pure culture was obtained. Gram staining revealed a gram – bacillus morphology, and a lack of endospores.

Azotobacter: Most growth occurred for enrichment and initial streaks. The three later restreaks produced less and less noticeable colony growth. Gram staining revealed large gram – rods, and the presence of endospores. [endospores?]

B. fastidiosus: Growth during enrichment process was not greatly detectable but present. Heat treatment followed by gram staining indicated the presence of endospore forming gram – rod [Should have been Gram +] shaped bacteria. The heat treatment appeared to kill off non-endospore forming bacteria.

Extreme Halophile: The enrichment culture did not successfully promote the growth of Extreme Halophillic bacteria. Subsequent plating also revealed no growth. Naturally, no further test were completed.


Upon examination of the results, the experiment was successful in isolating specific groups of bacteria from others taken from their natural environment. The growth conditions for each species were selective in isolating a certain species and inhibiting the growth of others. This process allowed the technicians to study such distinguishing characteristics such as morphology, and the information of endospores. For further details on the results of the experiment please refer to the included chart diagramming the results clearly. What made this experiment successful was the fact that the growth conditions were specifically selective in isolating the targeted bacteria. Below is listed the key conditions for each species that made it selective for only its growth:
Thermophile: Since thermophiles have the ability to live and thrive at very high temperatures, it gives them a distinct advantage over other bacteria that cannot survive in such conditions. To keep an element of consistency in the experiment, cultures were grown at 25, 32, and 55 degrees Celsius. Results indicated that the most growth occurred at the lower temperatures and the least at 55 degrees. This indicated that the majority of the sample must have been non-thermophillic bacteria able to grow at fair temperatures. The remaining colonies present on the 55-degree plate are extreme thermophillic bacteria, capable of living at such high temperatures.
Actinomycete: Since the natural environment of these bacteria is soil, it was not tremendously difficult to obtain samples of them. What makes actinomycetes interesting is their ability to grow well on low concentrations of many kinds of compounds. Other bacteria may lack the metabolic ability to be so diverse and adapting. GLA plates were chosen as the growth medium, as they possess very low concentrations of many compounds. This condition is not favorable to all bacteria, therefore it is selective for its growth only.
Agar Decomposer: What makes the agar decomposing bacteria so unique, is its ability to metabolize the complex polysaccharides, which contain sulfur esters in marine algae. Agar is a unique substance in that it contains much of the content of seaweed. When choosing the natural environment for such bacteria, it was clear that a piece of seaweed would be most logical place to start looking. [good] The conditions for such bacteria are selective in the sense that not all bacteria possess the metabolic capability of decomposing agar.
Azobacter: It is a known fact that bacterial species share a natural environment. A broad environment such as soil makes it quite difficult to isolate a specific species with simple Nutrient Agar streaking methods. Since Azobacteria are nitrogen fixing, the use of Mannitol Nitrogen Free [OK, But why mannitol?] Plates creates a selective environment for their growth.
B. fastidiosus: The eating habits of this bacteria made its isolation quite capable. Considering that this bacterium will not use glucose as its carbon source, but will use uric acid, the conditions can be replicated and its isolation achievable. Many bacteria are unable to use uric acid as its food source. This again, creates the desirable selective environment for its isolation.
Extreme Halophile: As the name implies, these bacteria are capable of thriving in conditions where the salt content is unbearable for other species. In choosing to use both Mediterranean Sea Salt and a Fish Sauce, both of which are highly hypersaline in composition. For this aspect of the experiment, the enrichment culture did not have any colony growth in it. In any case, the highly salty environment is not hospitable to all bacteria, making it very selective for the growth of extreme halophillic bacteria.
[Good job. Your introduction was clear, concise and presented all the necessary information. The results section contained, just that, results. You did a good job discussing the selective pressures of your isolations in the “discussion section.” And did so without having to repeat the results section. Overall an excellent report.]