696 MICROBIOLOGY
in Figure 11. These models are called Winogradsky columns.
The variety of microbial life which develops over a period
of 2–10 days is determined by (a) the degree of acidity or
alkalinity of these natural growth media, (b) the nutrients
contained in the liquid and solid phases, and, of course,
(c) the initial populations of microorganisms. In the exam-
ples shown, light is provided to ensure growth of photosyn-
thetic organisms.
If the basic principles of the Winogradsky column are
to be used to reveal the microbial population in a particular
soil or water sample, then the column and all its components
are fi rst sterilized and then inoculated with a nonsterile soil
or water sample. The microbial population of the sample
will develop in the portions of the column which provide the
proper physical and chemical conditions.
An important application of Winogradsky columns can
be made for testing various chemicals for potential ecologi-
cal changes. The chemical agent is percolated through a
soil column or is simply added to a predominantly liquid
column either when the column is started or after its micro-
bial population has developed. Signifi cant changes in
the column’s normal population (diversity or population
density) is indicative of toxicity to one or more types of
microorganisms. The profound changes in populations of
higher plants and animals due to disruption of the balance
of microbial life can be readily appreciated when the cyclic
nature of nitrogen and sulfur dissimilation is considered
(Figures 12 and 13). These interdependences emphasize
the key role played by microorganisms in maintaining the
balance of soil nutrients.Use of the Winogradsky Column for Testing
Biodegradability Capacity of a Natural Soil or
Water BodyIn the last section, an example was given in which one of
these bodies with little capacity for biodegradation of a
weed-killer can be controlled so that the body in question
does not spread the potential pollutant to a bordering body.
We now consider a method for pretesting the biodegrada-
tion test. One would hope that this or a parallel test would
become standard before new agricultural chemicals are mar-
keted. That is, chemicals which are not decomposed before
they leave the immediate land or water body in which they
are used would not be marketed or would only be marketed
after controls against accumulation of the chemical had been
worked out.
The Winogradsky column test for ability of a potential
soil or water body to degrade a potenlially dangerous chemi-
cal such as a weed-killer consists of (a) preparing a standard
column composed of soil or water from the body in ques-
tion, and (b) after the column has been allowed to develop
its natural population (c) an isotopically labelled version of
the weed-killer can be added in the concentration (and 10
the concentration that the weed-killer is to be used). After a
time equivalent to that in which the weed-killer is expected
to remain in the natural body (i.e. account for fl ushing time
from rain or water currents), the column is tapped by elution
with water or buffer, and the effl uent is analyzed for per cent
undergraded weed-killer as well as the nature of the deg-
radation products. The latter point is particularly importantTABLE 5
Nutritional requirements of typical heterotrophic microorganisms with limited synthetic capacityType compound Example Quantity in typical medium (%)Energy source Glucose, sucrose,
glutamic acid,
succinic acid0.12.0%
0.10.5%Synthesis of
protein and fatsodium acetate 0.010.1%Lecithin
amino acids0.0010.005%
0.0020.1%
Synthesis of
nucleic acidspurines and
pyrimidines0.00050.002%Coenzymes Vitamins 0.00010.005%
Major inorganic
requirementsPO 4 , Mn,
Mg, Na, K0.010.05%Minor inorganic
requirementsCa, Co, Zn,
Fe,Cu, Cl
NH 4 or NO 3 0.0010.01%Water All the above are
prepared in aqueous
solutionC013_004_r03.indd 696C013_004_r03.indd 696 11/18/2005 10:42:01 AM11/18/2005 10:42:01 AM