Some Observations of Purple Sulfur Bacteria
Associated with Waste Stabilization Ponds
JAMES C. MEREDITH, Engineering Consultant
U. S. Public Health Service
Oklahoma City, Oklahoma
FREDERICK G. POHLAND, Associate Professor
School of Civil Engineering
Georgia Institute of Technology
Atlanta, Georgia
INTRODUCTION
The red or pink color that occasionally develops in waste stabilization ponds
may be caused by the proliferation of purple sulfur bacteria. Their appearance and
relative dominance are generally associated with anaerobic conditions and orgainic
loadings sufficiently high to cause depletion of the oxygen supply, a reduction in the
hydrogen sulfide odor noticeable before the purple sulfur bacteria appear, and
changes in color of the pond to various shades of brown, red or pink.
The purpose of this investigation was to study the behavior of a culture of
purple sulfur bacteria obtained from a waste stabilization pond and subjected to
varying environmental conditions.
TAXONOMICAL CONSIDERATIONS
As reported by Van Niel (1), the purple sulfur bacteria represent one of three
families of photosynthetic bacteria:
1. Thiorhodaceae - the purple sulfur bacteria among   which   the   best
known are species of Chromatium and Thiospirillum.
2. Chlorobacteriaceae - the green sulfur bacteria represented by the genera
Chlorobium and Chloropseudomonas.
3. A'thiorhodaceae - the nonsulfur purple bacteria represented by the genera Rhodomicrobium, Rhodopseudomonas, and Rho do spirillum.
The purple bacteria found in natural habitats represent an assortment of morphological types which differ in shape, size, color, and aggregation patterns. Winogradsky
(2) subdivided the family, Thiorhodaceae, into thirteen genera. The description of
these genera were based on observations of organisms collected from natural habitats
without pure culture isolation. Nutrient media and methods for obtaining pure cultures of certain purple sulfur bacteria have now been developed. The morphological
uniformity of such cultures supports Winogradsky's original classification of thirteen
genera in this family.
Two of the best known genera of the family Thiorhodaceae are Chromatium
and Thiospirillium (1). Chromatium spp. are ovoid to vibrioid in shape and are motile
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