Home >> Science & Nature >> Science

How to Determine the Characteristics of Bacteria

Bacteria are small, simple, single-celled organisms and are believed to be the oldest organisms that existed on the Earth. Bacteria have the greatest distribution of any other living thing on earth and can be found in the air, soil, water and within other living organisms, such as humans. Some bacteria have adapted to even the most extreme environments. Bacteria can be autotrophic or heterotrophic. Bacteria can be further subcategorized based upon whether they use light, and whether they receive nutrition from organic or inorganic sources. Most prokaryotes are heterotrophic, meaning that they obtain nutrients from the surrounding environment. Autotrophs synthesize their own food. Bacteria can be harmful or helpful depending on the type and density in their environment.

Things You'll Need

Lab microscope
Bacteria cultures
Lab worksheet
Pencil

Instructions

- 1
  Obtain live bacteria cultures for study. Some of the cultures that you can examine are Escherichia coli, Streptococcus faecalis, Corynebacterium xerosis, Staphylococcus saprophyticus, Streptomyces albus, Serratia marcescens and Micrococcus luteus. However, any number of different types of bacteria can be examined for classification. These cultures can be ordered beforehand from a science education supply outlet.
- 2
  
  This bacteria is harmful to humans and has been responsible for high-mortality epidemics.
  
  View the bacteria culture under the microscope and record observations noting the amount of growth within a four-hour and then a 24-hour time period. Note the coloration of the organism. Test the organism to see if pigmentation occurs within the organism itself or if the pigmentation is water soluble, diffusing into the surrounding environment. Observe and describe the opacity of the medium in which the organism is growing which indicates surface growth of the bacteria.
- 3
  
  This bacteria is predominant in North America and is the agent for Lyme disease.
  
  Classify bacteria by testing for motility and as a presumptive test for the presence of flagella. The flagella is a whip-like tail that propels the bacteria. By placing the culture in a semisolid motility medium, and determining the location or spread of the bacteria within 24 hours, you can classify the bacteria according to motility and as to the presence of flagella. A typical motility medium consists of enyzmatic digest of gelatin (10 grams), beef extract (three grams), sodium chloride (five grams) and agar (four grams). The pH should be 7.3, plus or minus 0.2 at 25 degrees Celsius. Bacteria which are considered motile, indicating presence of flagella, extend outward from the line of inoculation in all directions.
- 4
  
  The azotobacter chroococum bacteria is a nitrogen-fixing bacteria which contributes to healthy soil.
  
  Observe and document the form of growth of the bacteria within the culture. Observe if it demonstrates a uniform growth along the line of inoculation, margins of growth have a toothed appearance, the growth is thin and veil-like, it manifests a branched growth within the culture or it appears to have roots in its growth structure.

Science