Evaluation of Caulobacter as an Inhibitor of
Acid Mine Drainage Formation
ROBERT A. BAKER, Director
Environmental Sciences
Teledyne Brown Engineering
Huntsville, Alabama
ALBERT G. WILSHIRE, Junior Fellow
Carnegie-Mellon University
Mellon Institute
Pittsburgh, Pennsylvania
INTRODUCTION
The presence of chemoautotrophic, acid-producing bacteria in acid mine
drainage has been observed by many investigators. The specific role of these
organisms in the production of acid mine drainage from the oxidation of pyrite
associated with coal is still not clearly defined. If the chemoautotrophs actually
promote production of acidic constituents, then eliminating them or reducing their
growth and reproduction should serve to reduce acid discharge. Chemical and
biological inhibitors are being considered. A likely biological inhibitor would be a
viable, proliferating parasitic organism capable of surviving in the mine waters. Once
such a parasite was established as part of the system microflora, it would not require
replenishment as would chemical inhibitors. Shearer, et al (1, 2) have suggested that
certain strains of Caulobacter are inhibitory to chemoautotrophic acid producing
organisms. Their recommendation was based on batch laboratory culture studies and
on continuously-operated, chemoautotrophic-containing laboratory coal pile
systems. They claimed that the Caulobacter had first been adapted to synthetic acid
mine drainage of pH 3.6 in the presence of very small amounts of peptone prior to
inoculation into the coal piles. This finding was at variance with previously published
information regarding Caulobacter.
The genus Caulobacter was proposed by Henrici and Johnson (3) as a member
of the order of stalked bacteria, Caulobacteriales. Although they did not succeed in
isolating Caulobacter, they were able to maintain them as components of a mixed
microflora in liquid media containing cellulose and chitin which had been inoculated
with lake water. Caulobacter were characterized as gram-negative, unicellular stalked
bacteria with the stalks arising from one pole of the cell. Cell shape varied depending
on cultural environment and age. They noted vibroid, rod or fusiform shaped cells
which multiply by transverse binary fission. A small swelling at the distal end of the
stalk was interpreted as a holdfast. Houwink (4, 5) succeeded in isolating several
strains from tap and canal waters. Bowers, et al (6) isolated a stalked bacterium from
well water which they identified as Caulobacter vibroides as described by Henrici and
Johnson. Nutritional studies by Grula, et al (7) revealed that this isolate is a strict
aerobe requiring riboflavine for growth in glucose-ammonium salts medium. The
attachment of Caulobacter to other microorganisms has been reported by the
following investigators: Kandler, et al (8), Houwink (5), Hund and Kandler (9),
Zavarizin, (10), and Poindexter (11). This ability is the result of the adhesive
property of the holdfast material. A common cultural trait of Caulobacter is the
formation of rosettes by clumping together via the holdfast. This was first observed
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