The Role of Microorganisms in the Ecosystem

 

Microorganisms are ubiquitous in the environment, where they have a variety of essential functions. Many microbes are uniquely adapted to specific environmental niches, such as those that inhabit the Dead Sea (Halobacterium), the bacteria and cyanobacteria that inhabit the boiling water springs in Yellowstone National Park, and Chlamydomonas nivalis, the algae that causes "pink snow." Microbes also play an essential role in the natural recycling of living materials. All naturally produced substances are biodegradable, which means that they can be broken down by living things, such as bacteria or fungi. Composting is biodegradation at its best. An examination of conditions that foster or impede composting gives insight to growth conditions of microorganisms as well as the proper function of the ecosystem.

 

(This experiment can easily be modified to accommodate focusing on different concepts, student numbers, time frames, etc. Students will generally be more receptive to the information if they play an active role in the development of the activity, such as obtaining soil from different sites and observing the rate of degradation of different items that they provide.)

Materials per pair (or more) of students:

Protocol:

  1. Divide students into groups of at least five.
  2. Give each student or pair of students a pot of soil from the same location.
  3. Have each student or pair bury the same item to approximately the same depth.
  4. One student or pair should serve as the control. This sample (A) will receive no additional treatment, but should be kept at room temperature.
  5. One student or pair in each group should serve as the minimal water treatment. This sample (B) will be watered with approximately 3 tbsp. (amount depending on size of container) weekly to simulate a dry climate. B should be kept at room temperature.
  6. Another student or pair in each group could serve as the cold treatment. This sample (C) should be maintained at about 4*C, which is standard refrigeration temperature.
  7. Another student or pair in each group could serve as fertilizer or aeration treatment. This sample (D) will be watered with liquid fertilizer weekly or stirred (sample E) weekly to provide air. Samples D and E should be kept at room temperature.

    Note: Scientists found that the addition of nitrogen and phosphorous could greatly speed the rate of degradation. This process is termed "bioaugmentation". Aeration also speeds the rate of decay, which explains the need for "turning" a compost pile.

    (Other variables: temperature, exposure to light, different objects, the addition of organic fertilizer such as manure, etc. The number of variables could be determined by the number of students participating or by the degree of difference students are capable of determining.)

  8. After one month, at weekly or longer intervals, students should dig-up the object and record its appearance. At least six weeks should be allowed for substantial degradation to become evident. Longer incubation might be needed to determine if some substances are biodegradable.

    (This activity might be well suited for scheduling when there will be a holiday break from school or mid-term exams. Students may tire of investigating the sample frequently if there are not noticeable changes.)

  9. This experiment allows for cooperative learning and permits a variety of formats for reporting results/conclusions. Many other skills could be utilized to make this more interesting. A simple lab sheet documenting observations is included. However, students could be encouraged to develop a poster presentation, a video taped "commercial" presentation, etc.

    Students could be asked to collaborate on designing an ideal landfill to accommodate a specific climate or topographic location, utilizing the information that they have gathered from this experiment.



The term bioremediation is defined as the use of microorganisms to remove or detoxify undesired or toxic chemicals from the environment. While it was an unfortunate incident from the environmental and economic perspectives, a tremendous amount was learned about bioredmediation from the Exxon Valdez oil spill in 1989. When the supertanker ran aground near Prince William Sound, Alaska, 11 million gallons of oil spilled into the water and washed onto the beaches. Through experimentation, scientists found that spraying the affected areas with non-organic nutrients, which selected for the naturally occurring microorganisms that could degrade oil and resulted in an increase in the numbers of those cells and an increased rate of degradation. Bioaugmentation is defined as the addition of necessary nutrients required to speed up the rate of degradation of a contaminant. Oil is rich in carbon and sulfur, but the organisms capable of degrading it also require nitrogen, phosphorous and oxygen. The addition of nitrogen and phosphorous in the form of fertilizer and the churning of soil or water to provide oxygen greatly speed the rate of clean-up. The cost of the Valdez clean-up is estimated at $1.5 billion. A spill of that magnitude required human as well as microbial clean-up.

While microorganisms are very effective at degrading naturally occurring substances, they have even been shown to effectively degrade some xenobiotic compounds, those that are chemically synthesized and do not exist naturally. Herbicides and pesticides are common xenobiotics that contaminate the environment. A sulfate reducing bacterium Desulfomonile has been associated with the degradation of chlorinated pesticides. This is of great interest to environmentalists, since chloroaromatic compounds are among the most frequently detected groundwater contaminants in the United States.

Studies of rates of biodegradation indicate that many synthetic polymers are not degraded by microorganisms and remain unchanged in landfills for decades. This knowledge has led progressive companies to utilize microbially produced, therefore biodegradable, alternatives to synthetic polymers such as plastics. The Wella company in England markets shampoo packaged in a bottle made of microbial plastic. Microbial lipid storage compounds can be regulated by controlling growth conditions to yield products with the desired qualities. Students might enjoy a study of packaging substances to determine if any are naturally produced and hence biodegradable.

 

Biodegredation

 

Record results in chart below.
Item Moisture

Condition

4°C       Room
Temperature
37°C      
Styrofoam
Pellets
Dry

RED

+Water

CLEAR

+Water +Booster

YELLOW

+Fert +Booster

BLUE

Cornstarch
Pellets
Dry

RED

+Water

CLEAR

+Water +Booster

YELLOW

+Fert +Booster

BLUE

Granny Smith
Apple
(quarter size)
Dry

RED

+Water

CLEAR

+Water +Booster

YELLOW

+Fert +Booster

BLUE

 

This activity can be performed in a variety of ways; this is only one scheme that is feasible. There are multiple variables introduced in this activity. The need for a control for each variable should be discussed.

 

Cups are color coded to represent moisture/ condition in order to minimize confusion:

*Cups were set up on DATE. 3 tablespoons (* 45 mL) of liquid were added at weekly intervals. Cups were maintained at the termperature indicated.

 

If a balance is available, the initial and final weights of the sample could be determined. The amount of loss and percentage degradation could then be calculated. If no balance is available, degradation can be recorded by estimating the portion of the apple that is absent. The following rating system has been useful:
      +    &nbsp  = 25% or less of the apple/sample is gone
      ++     = 50% of the apple/sample is gone
      +++   = 75% of the apple/sample is gone
      ++++ = 100% of the apple/sample is gone nothing remains