of a “Good” Report]
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
Actinomycete, Agar Decomposer, Azobacter, Bacillus fastidiuos,
The various natural environments and procedures for their isolation will be
explained and diagramed in the following section.
refer to pages 55-59 of the Fundamentals of Microbiology Laboratory Manual,
printed by the University of Connecticut Department of Molecular and Cell
For each of the organisms targeted and isolated, please note the appropriate
protocol changes listed below:
A small amount of soil taken from on campus was used.
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.
addition to growing the culture at 55 degrees, it was also grown at 25 degrees
and 32 degrees Celsius.
After the enrichment culture was streaked onto the initial GLA
three additional T-streaks were done in order to isolate a pure culture.
A small piece of seaweed taken from Long Island sound was
as the source of bacteria.
the initial enrichment culture was streaked, 6 additional T-streaks were
carried out in order to isolate a pure culture.
After streaking the initial enrichment culture, four additional T- streaks
were carried out in order to obtain a pure sample.
After streaking the initial enrichment culture, four
additional T-streaks were done in order to gain pure culture. (For
addition to the uric medium the culture was grown on, a Nutrient Agar medium
was also used in order to observe growth.
There was no additional T-streaks carried out after the
(No growth occurred).
refer to the included Flow Chart Pages for a Diagrammatic View of Methods*
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:
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.
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
were not endospores just spores]
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.
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.
during enrichment process was not greatly detectable but present. Heat
treatment followed by gram staining indicated the presence of endospore forming
gram – rod
have been Gram +]
shaped bacteria. The heat treatment appeared to kill off non-endospore forming
enrichment culture did not successfully promote the growth of Extreme
Halophillic bacteria. Subsequent plating also revealed no growth. Naturally,
no further test were completed.
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
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.
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.
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.
conditions for such bacteria are selective in the sense that not all bacteria
possess the metabolic capability of decomposing agar.
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
But why mannitol?]
creates a selective environment for their growth.
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.
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.
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.]