Encyclopedia of Environmental Science and Engineering, Volume I and II

MICROBIOLOGY 691

protozoa and fruiting bodies which produce spores with cell

walls like fungi. There are two major subdivisions (a) Cellular

and (b) Acellular. They both primarily live on decaying plant

material and can ingest other microorganisms, such as bacte-

ria, phagocytically. Both have life cycles, but that of the acel-

lular slime molds is more complicated.

Cellular slime molds have vegetative forms composed of

single ameboid cells. Cyclically, ameboid cells aggregate to

form a slug-shaped pseudoplasmodium that begins to form

fruiting bodies when the slug becomes immotile. Spores are

fi nally produced by the fruiting bodies.

Acellular slime molds have vegetative forms called plas-

modia which are composed of naked masses of protoplasm

of indefi nite size and shape and which travel by ameboid

movement (protoplasmic streaming). Two kinds of nesting

structures are produced: fruiting bodies (part of the sexual

cycle) and sclerolia.

Protozoa

The last major group of microorganisms are the protozoa.

As already stated, it is very hard to distinguish plants from

animals at this primitive stage in evolution where organisms

have some attributes of each. Most workers therefore are less

interested in whether protozoa should be claimed by bota-

nists or zoologists as they are in studying the group as the

root of a phylogenetic tree which gave rise to clearly sepa-

rable plants and animals. Protozoa range in size from that

of large bacteria to just visible without a microscope. They

have a variety of shapes, multiplication methods and associ-

ations which range from single cells to specialized colonies.

They are variously found in fresh water, marine, terrestrial,

and occasionally, aerial habitats. Both freeliving and para-

sitic forms are included. Most are motile but there are also

important nonmotile forms. The protozoa are divided into

four subphyla (I–IV).

I. Sarcomastigophora include forms which have either fl a-

gella, pseudopodia or both. Usually a single-type of nucleus

(though opalinids contain multiples of this one type) is pres-

ent except in development stages of a few forms. Asexual

reproduction by binary fi ssion is common. One whole class

contains chloroplasts and are claimed by both protozoolo-

gists and algologists (they are considered here in detail with

the eukaryotic algae). Many important parasites of diverse

animal and some plant groups are found here. Sexual repro-

duction is present in a few forms.

The Sarcomastigophora are divided into three super-

classes.

A. Mastigophora ( fl agellates ) Are further sub-divided into

Phytomastigophorea or plant-like fl agellates (see eukaryotic

FIGURE 6 Bacterial motility. Motility is tested by

stabbing an inoculated needle into a tube of very vis-

cous growth medium. The motile organisms (S. typhi

and P. vulgaris) grow away from the stab mark.

4

3

5

1

2

FIGURE 7 Isolation of single bacterial colonies

on agar plates by dilution streaking. A diagrammatic

representation of method of streaking inoculated

needle across nutrient-containing plate. Stippled

area is the primary inoculation. The inoculation

needle is then flamed to sterilize and is then drawn

across the stippled areas as indicated for area 1.

The needle is then resterilized and drawn across

area 2, etc.

FIGURE 8 Isolation of single colonies by pour plate

technique.

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