Environmental Engineering Reference
In-Depth Information
importance of classifying organisms cannot be overstated, for without a clas-
sification scheme establishing criteria for identifying organisms and arrang-
ing similar organisms into groups would be difficult. Probably the most
important reason for classifying organisms is to make things less confusing
(Wistreich and Lechtman, 1980). Linnaeus was innovative in the classifica-
tion of organisms. One of his innovations still with us today is the
binomial
system of nomenclature
. Under the binomial system, all organisms are gener-
ally described by a two-word scientific name:
genus
and
species
. Genus and
species are groups that are part of a hierarchy of groups of increasing size,
based on their nomenclature (taxonomy):
Kingdom
Phylum
Class
Order
Family
Genus
Species
Using this hierarchy and Linnaeus' binomial system of nomenclature, the
scientific name of any organism indicates both the genus and the species.
The genus name is always capitalized, and the species name begins with
a lowercase letter. On occasion, when little chance for confusion exists, the
genus name is abbreviated with a single capital letter. The names are always
in Latin, so they are usually printed in italics or underlined. Microbe names
of interest to the drinking water practitioner include
•
Salmonella typhi
, the typhoid bacillus
•
Escherichia coli
, a coliform bacteria
•
Giardia lamblia
, a protozoan
Escherichia coli
is commonly known as simply
E. coli
, and
Giardia lamblia
is
usually referred to by only its genus name,
Giardia
.
The water sciences use a simplified system of microorganism classifica-
tion that is broken down into the kingdoms of animal, plant, and protista.
As a general rule, the animal and plant kingdoms contain all of the mul-
ticell organisms, and the protists contain all of the single-cell organisms.
Along with microorganism classifications based on the animal, plant, and
protist kingdoms, microorganisms can be further classified as being
eucary-
otic
or
procaryotic
(see
Table 6.1
). A eucaryotic organism is characterized by
a cellular organization that includes a well-defined nuclear membrane. A
procaryotic organism is characterized by a nucleus that lacks a limiting
membrane.
