The ability of Sphingomonas
paucimobilis, strain
EPA
505 (a soil bacterium capable of utilizing
fluoranthene as the sole source of carbon and energy
for growth) to metabolize a variety of high molecular
weight polynuclear aromatic hydrocarbons (PAHs)
was investigated. After 16 h of incubation with 10
ppm
of a PAH, a resting cell suspension (1 mg wet cells/mL) of S.
paucimobilis grown on
fluoranthene
degraded 80.0, 72.9, 31.5, 33.3, 12.5, and 7.8% of
pyrene,
benz[a]anthracene (B[a]A), chrysene,
benzo[a]pyrene
(B[a]P), benzo[b]fluoranthene (B[b]F),
and
dibenz[a,h]anthracene
(DB[a,h]A), respectively. No
degradation of dibenzo[a,l]pyrene was
detected
under these conditions. 1-Nitropyrene was degraded
at a lower rate than pyrene. The extent of
degradation
of the PAHs increased with an increase in cell
density. Studies with [7-14C]B[a]P and
[5,6,11,12-14C]chrysene showed that, after 48 h of incubation, the
cells degraded nearly 28 and 42% of [14C]B[a]P
and
[14C]chrysene to 14CO2,
respectively, suggesting that
the bacterium is able to metabolize B[a]P and chrysene
via ring cleavage. No evolution of
14CO2 was detected
from cultures incubated with
[4,5,9,10-14C]pyrene or
[1,2,3,4,4a,4b-U-14C]dibenz[a,l]pyrene.
Analysis of
the ethyl acetate extracts of the culture medium by
reverse-phase HPLC showed that B[a]P, B[b]F, and
B[a]A were each degraded to the major, high polar
metabolite(s). The degradation of B[a]P with
S.
paucimobilis significantly reduced the mutagenic
activity
associated with the hydrocarbon. The addition of
solubilizing agents such as Tween 80 or cyclodextrin
to the incubation medium did not enhance the
biodegradation of B[a]P by EPA 505. The addition of
5 ppm of B[a]A, chrysene, fluoranthene, or DB[a,h]A to the incubation medium containing 5 ppm of
B[a]P had no effect on the degradation of B[a]P by
EPA 505. However, the biodegradation of B[a]P was
reduced by nearly 30% in the presence of 5 ppm
of B[b]F. The results demonstrate that S.
paucimobilis
EPA 505 has the ability to degrade several four- and five-ring PAHs ranging in molecular size, shape, and
chemical structure.
