Environmental Engineering Reference
In-Depth Information
RHA1 was indicated by nonstoichiometric yield of 2-chlorobenzoic acid
(2-CBA) and the appearance of yellow color with a maximum absorbance at a
wavelength of 394 nm, 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid
(HOPDA). Some fading of the yellow color and a shift toward shorter wave-
lengths were detected during the next two days of incubation, indicating further
transformation of the meta-cleavage product; however, no increase of 2-CBA
concentration was noted, indicating no complete transformation. Accumulation
of the 2-CB meta-cleavage product was also detected during incubation of 2-CB
with NY05, but in contrast to strain RHA1, this intermediate completely dis-
appeared after 24 h of incubation followed by equimolar production of 2-CBA.
In a difference from the other three strains, the dynamics of accumulation of
2-CBA from 2-CB by LB400 suggested that it could further degrade this acid
(40 to 60%) with no metabolites of 2-CBA degradation found (HPLC).
2,6-CB proved to be the congener most resistant to microbial attack, with
less than 5% depletion by NY05 and VP44, and only 5 to 10% degradation
by strains LB400 and RHA1, yielding up to 5% as 2,6-CBA. Accumulation
of HOPDA during incubation of RHA1 with 4-CB, 2,4-CB, and 2,6-CB indi-
cated incomplete transformation of some of the (Cl)HOPDAs formed from
these congeners into the corresponding chlorobenzoic acids and pentadienes.
Congeners with one of the rings containing chlorine in the para-position
(2,4′ and 2,4,4′-CB) were efficiently degraded by LB400 and RHA1 via pref-
erential oxidation of their ortho-substituted rings, in agreement with the
previously reported transformation of 2,4,4′-CB by LB400 (Seeger et al., 1995).
Interestingly, following a decrease in absorption of HOPDA (434 nm), during
a longer (24 h) incubation of LB400 with 2,4,4′-CB, a minor peak of HOPDA
with a maximum of 398 nm was observed, suggesting that the 4′-chlorinated
ring of 2,4,4′-CB could also be oxidized. This was confirmed by GC/MS
(mass spectrometry) verification of minor 2,4-CBA production among the
degradation products of 2,4,4′-CB (Maltseva et al., 1999). Complete depletion
of 2-4′- and 2,4,4′-CB was also observed with NY05 and VP44; however,
amounts of chlorobenzoates formed did not exceed 10 to 12% of the expected
value, in agreement with formation of high amounts of (Cl)HOPDA. The
metabolite of 2,4-CB was characterized by molecular ion at m/z 430 (mass
to charge ratio), low abundance of M ± 15 and M ± 35 ions, and a prominent
ion M ± 117 arising from the loss of CH
3
, Cl, and COO-TMS (trimethylsilane)
from the molecular ion, respectively. The same fragmentation pattern was
obtained for the metabolite of 2,4-4′-CB (molecular ion 464). The mass spec-
tral features of these compounds are in good agreement with previously
published mass spectra of the TMS derivatives of chlorobiphenyl meta-cleav-
age products (HOPDAs) produced by other bacterial strains (Furukawa et
al., 1979a, 1979b; Masse et al., 1989). Absorption maxima of these HOPDAs
occurred at 398 nm indicated that they have the chlorine substituent at the
ortho-position (Seeger et al., 1995) and therefore were formed by oxidation
of the para-chlorinated ring. Although both strains produced some
2,4-CBA from 2,4-4′-CB, only NY05 produced traces of 2-CBA from 2,4′-CB
as transformation product. No significant decrease of these HOPDAs, nor a
