Nuclear magnetic resonance spectroscopic studies on the microbial degradation of mononitrophenol isomers

The biochemical pathways followed by a
mixed bacterial culture and one of its constituent
strains, Sarcina maxima, MTCC 5216 (hitherto unreported)
during the degradation of mononitrophenol
isomers was studied using extensive nuclear magnetic
resonance (NMR) spectroscopy (One- and Two-
Dimensional Heteronuclear Multiple Quantum
Coherence Transfer-2D HMQCT NMR). NMR
investigations revealed that o-nitrophenol (ONP)
could be degraded by the consortium to metabolites
such as catechol, cis, cis-muconic acid, c-hydroxymuconic
semialdehyde, maleylacetate and b-ketoadipate.
The spectra of ONP reaction mixture degraded by
S. maxima showed that formation of maleylacetate
from c-hydroxymuconic semialdehyde should go
through a new metabolite c-hydroxymaleylacetate,
hitherto unreported. The consortium could breakdown
m-nitrophenol (MNP) to 4-aminocatechol indicating
that it came from 3-hydroxyaminophenol. However, S.
maxima MTCC 5216, could convert MNP to hitherto
unreported 2-nitrohydroquinone and the subsequent
2-hydroxylaminohydroquinone to 1,2,4-benzenetriol
along with c-hydroxymuconic semialdehyde, muconolactone
and maleylacetate. The pathway followed by
the consortium during p-nitrophenol (PNP) degradation
was by the formation of 4-nitrocatechol, maleylacetate
and b-ketoadipate. PNP reaction mixture of
S. maxima, MTCC 5216 on the other hand, showed that
the pathway could proceed through the formation of
p-hydroquinone as the initial metabolite. The present
study conclusively established the nitrophenoldegrading
ability of both the consortium and S. maxima
MTCC 5216, including exhibiting slight deviations
from the pathways followed by the other reported
microorganisms.