Utilization of Resistant Proteins by
Activated Sludge
GEORGE J. CAPESTANY, Water Quality Analyst
Municipality of Metropolitan Seattle
Seattle, Washington
DALE A. CARLSON, Associate Professor
Civil Engineering Department
University of Washington
Seattle, Washington
INTRODUCTION
The behavior of activated sludge toward amino acids and more or less complex polypeptides has been investigated by several authors. Our primary purpose
in this study was to gain some insight of the biochemical, microbial and physical
behavior of an activated sludge culture when presented with a truly complex protein molecule.
We found the keratins to be a remarkable example of complexity and strength
and a true challenge to the microbial systems. Human hair, of obvious availability, and commercial purified keratin were chosen materials.
In general, protein from mammalian hair, hooves and nails, bird feathers,
and reptile scales all can be grouped under the general classification of keratins.
The remarkable evolutionary process that brings about the transformation of ordinary protein into keratin takes place mainly as a structural transformation of
bonding and crosslinking which transforms the protein into a material resistant to
chemical agents as well as to the biological environment (1). Moreover, the
structural peculiarities of a keratin leaves a relatively small pathway of attack to
proteolytic saphrophytic organisms, even though it contains the proper amount and
ratios of carbon and nitrogen to sustain microbial life.
The term keratin is applicable to proteins that are insoluble in hot water, organic solvents, dilute bases, and acids, and are resistant to digestion by pepsin and
trypsin. Keratin could be defined as protein stabilized by covalent disulfide linkages.
The keratins possess the same structural arrangement as all other fibrous proteins with the exception that their sulfur content is higher and has the form of disulfide bonds which have been shown to be the primary responsible agents for keratin stability (Figure 1). The disulfide bond forms a dihedral angle of 90 degrees
hindering rotation around it.   It possesses a bond energy of 60 kcal/mole (2).
It has been well established that microbial solubilization of wool in nature is
effected through a joint action of disulfide reducing agents and proteolytic agents.
Streptomyces fradie solubilizes 80 to 90 per cent of wood and feather keratin after
four days of incubation; and its culture broth without cells digests the protein two
times faster than either of two digestive enzymes, papain and trypsin (3).
EXPERIMENTAL TECHNIQUES
Preparation of cut hair for use in the experiment consisted of triple washing
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