Growth Responses of Certain Bacteria to
ABS and Other Surfactants
DEAN A. ANDERSON, Professor of Microbiology
Department of Microbiology and Public Health
California State College
Los Angeles, California
The present study as initiated in 1962 was prompted by the optimistic hope of
isolating a strain, or strains, of bacteria capable of effectively degrading commercial alkyl benzene sulfonate. At that time the publicity regarding the foam
producing activities of persistent, undegraded ABS was reaching its zenith and the
search for such organisms had preoccupied a considerable number of workers.
However, no investigator reported any startling successes. As the experiment
progressed and a further study was made of the current literature, the fact became
apparent that the search for a vigorous ABS degrader was probably a futile one.
This, coupled with impending governmental intervention halting the production
of the present molecular variety of ABS, made the search for actively degrading
strains of bacteria largely an academic matter. However, certain ABS-utilizing
strains had been isolated which showed interesting growth patterns on this and
other surfactants. The decision was made to continue a study of these bacteria
because of the possibility of gaining new insights and was independent of immediate utilitarian considerations.
The utilization of ABS by bacteria as a sole carbon source presents a dual
problem: (1) the essentially exotic nature of the molecular configuration of ABS,
and (2) the probably physico-chemical effect on bacterial metabolism resulting
from the marked reduction of surface tension at the surface of the cell membrane.
The molecular structure of one of the typical varieties of ABS (and of other
surfactants) is shown in Figure 1. A number of closely related molecular isomers
or variants which exhibit essentially the same properties may be present in commercial preparations of ABS. The source material is propylene gas (CH3CH:CH2).
Four of these molecules are polymerized to form propylene tetramer. These form
a hydrocarbon chain of about 12 carbons which is branched rather than straight,
with side chains of methyl (CH3) groups. Variation in linkage seems to occur as
a result of slight variations in the manufacturing process.
The propylene tetramer is then attached to a benzene molecule to form an
alkylated benzene. The point of attachment of the side chain to the benzene
ring is rarely on the terminal carbon of the propylene tetramer. Sulfonation with
sulfuric acia, followed by neutralization with sodium hydroxide, completes the
formation of a salt, sodium alkyl benzene sulfonate.
The branching of the alkyl chain appears to be the primary reason for the
lack of biodegradability in ABS. These unusual molecular configurations are
apparently rarely if ever encountered in nature. As a result no bacterial mutant
varieties have evolved which possess either the constitutive or induced enzymes
capable of the utilization of branched chain aliphatic hydrocarbons.
That certain, but not all, molecular varieties of ABS are attacked is evidenced by reports of 40-60 per cent degradation during sewage treatment. However, complete degradation has not been reported.
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