Observations on the Behavior of a
Microbial Population
Adapted to a Synthetic Waste
T.B.S. PRAKASAM, Research Assistant
NORMAN C. DONDERO, Professor
Department of Environmental Science
Rutgers - The State University
New Brunswick, New Jersey
There has been continuing interest in the adaptive responses of the microbial
flora of water, sewage, and waste treatment processes to nutrients, toxic materials, and other environmental influences. There are several mechanisms of
adaptation known for microorganisms: changes in the composition of population,
changes in the structures of the cells, and changes at the molecular levels of cell
contents (e.g. enzyme or gene molecules).
McKinney et al (1), employing Stanier's technique (2) which was developed
for pure cultures, reported that laboratory acclimated activated sludge exhibited
sequential enzymatic induction in the metabolism of aromatic compounds. Gaudy
(3) and Gaudy, et al (4) reported diauxic or biphasic growth in heterogeneous microbial population. These adapted sludges could not utilize sorbitol in trie presence
of glucose until glucose was completely utilized. The phenomenon was attributed
to parallel phenomena observed in pure cultures of microorganisms (5, 6) known as
enzyme induction and enzyme repression in which, respectively, enzymes are
formed in quantity by the cells only in the presence of a specific substrate and are
prevented from being formed by certain other substrates or their products. The interpretation of Gaudy's experiments rested upon the implicit assumptions that the
microbial population was typical of activated sludge, that the cells were active on
both glucose and sorbitol, and that there were no shifts in the population distribution during enzyme induction and repression.
If the acclimated sludge shows the heterogeneity of typical activated sludge,
which remains stable through the reported diauxic phenomenon, then the concept
of diauxie can be confirmed. A population shift would invalidate the interpretation of diauxie, but may be explained in other terms. Experiments were undertaken to investigate these points in the behavior of the microbial population of a
sorbitol-adapted sludge in the utilization of different substrates viz., glucose,
glucose plus sorbitol, and sorbitol. Efforts were made to characterize the population of the sludge adapted according to the methods of Gaudy (3).
EXPERIMENTAL STUDIES
Basal medium one and Basal medium two used in these studies were of the
same composition described by Gaudy (3), and Gaudy et al (4). The adaptation
technique described by Gaudy (3) was followed using the Basal medium one.
Bacterial counts were obtained by surface-plating homogenized settled sewage, activated sludge, and adapted sludge on three different agars (basal medium
one plus 1.5 per cent agar added for solidification) containing (a) sorbitol (300
mg/l),  (b) glucose (300 mg/l),   or (c) glucose plus sorbitol (300 mg/l of each).
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