Encyclopedia of Environmental Science and Engineering, Volume I and II

700 MICROBIOLOGY

memb rane is exposed and the desired amount of

air passed through it. Air-borne microorganisms

are trapped on or in the membrane. Some dis-

crimination among organisms can be made during

sampling by using membranes with graded porosi-

ties. In this way organisms are segregated accord-

ing to their cross-sectional dimensions. To reveal

the organisms impinged upon the membrane, the

membrane is treated as inoculum for the various

selecting media.

B. Water sampling techniques Any container which

can be sterilized and can be opened and closed

by remote signal can be used. It should be rec-

ognized that pressure changes after retrieval may

influence viability of organisms collected at great

depths.

C. Soil sampling techniques A sterilized coring device

is usually used to ensure against contamination

with airborne organisms. The soil samples are han-

dled aseptically and weighed amounts are tested

for their microbial population.

REFERENCES

1. Environmental Microbiology, in The Natural Environment and the Bio-
   ecochemical Cycles, O. Hutzinger, ed., Springer Verlag, Heidelberg,
   1985.


2. Saunders, V.A. and Saunders, J.R., Microbial Genetics Applied to Bio-
   technology, Croom-Helm, London, 1987.


3. Zehnder, A.J.B., Biology of Anaerobic Microorganisms, Wiley Inter-
   science, New York, 1988.


4. Fleckenstein, L.J., Release of Genetically Engineered Microorganisms
   to the Environment, Resource Management and Optimization, Vol. 6,
   no. 4, 1989.

HELENE N. GUTTMAN

US Department of Agriculture

Elemental sulfur

colorless aerobic sulfur

bacteria: Beggiatoa,

Thiothrix, Thiobacilli

SO 4 = Desulfovibrio

many microorganisms

plants and animals anaerobic putrefaction

bacteria

SH of amino acids

to make protoplasm

anaerobic, photosynthetic

bacteria

H 2 S

FIGURE 13 The sulfur cycle. Microorganisms are becoming increasingly useful for processing

low-grade sulfur-containing ores. Sometimes overlooked is the natural cyclic distribution of

sulfur-containing compounds in which microorganisms play principle roles.

MINE DRAINAGE: see POLLUTION FROM MINE DRAINAGE

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