25th International Meeting on Organic Geochemistry IMOG 2011

P-513
Anaerobic oxidation of plant-derived 3-phenylpropanoids by the
denitrifying bacterium ―Aromatoleum aromaticum‖ EbN1
Heinz Wilkes 1 , Kathleen Trautwein 2,3 , Ralf Rabus 2,3
1 Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, 2 Institute
of Chemistry and Biology of the Marine Environment (ICBM), University Oldenburg, Oldenburg, Germany,
3 Max Planck Institute for Marine Microbiology, Bremen, Germany (corresponding author:wilkes@gfzpotsdam.de)
Phenylalanine-derived 3-phenylpropanoids (e.g.
cinnamic acid, p-coumaric acid, ferulic acid, sinapinic
aicd) are widespread in nature. They represent the
building blocks of lignin, which is the second most
abundant terrestrial biopolymer after cellulose,
accounting for approx. 30% of the organic carbon in
the terrestrial biosphere [1]. As components of
secondary metabolites (anthocyanins, flavonoids or
phytoalexins) 3-phenylpropanoids play also an
important role in plant stress responses [2]. Release
of 3-phenylpropanoids into the environment arises
mainly from the biodegradation of plant material. In
accordance with the natural abundance, many
microorganisms are able to utilize 3phenylpropanoids.
Their metabolism has been
studied in a variety of bacteria, and different
degradation pathways have been proposed to be
employed by these bacteria.
Here we present results of studies on the metabolism
of 3-phenylpropanoids by the denitrifying bacterium
―Aromatoleum aromaticum‖ EbN1 under aerobic and
anaerobic conditions based on identification of
metabolites and differential protein profiling. Strain
EbN1 was originally isolated with ethylbenzene from
freshwater sediments and demonstrated to utilize a
large variety of aromatic compounds under anoxic
conditions [3]. This includes p-ethylphenol which is
oxidised via a degradation pathway reminiscent of
known anaerobic ethylbenzene degradation in the
same bacterium [4].
The present study revealed that strain EbN1 is
capable of utilizing cinnamyl alcohol, hydrocinnamic
acid, cinnamic acid, 3-(4-hydroxyphenyl)propanoic
acid, p-coumaric acid, m-coumaric acid, 3-(3,4dihydroxyphenyl)propanoic
acid and caffeic acid
under anoxic conditions. GC-MS analysis of
metabolites formed during growth with these
substrates provided evidence for their degradation via
a �-oxidation pathway as outlined for
hydrocinnamic/cinnamic acid in Figure 1. 3-Hydroxy-
3-phenylpropanoate was strongly prevailing upon
growth with hydrocinnamate and cinnamate while the
respective substrate as well as benzoate were
present in small relative amounts only. This could
indicate that the hydration of cinnamoyl-CoA takes
place at a high rate while one of the following steps
required to form benzoyl-CoA from 3-hydroxy-3phenylpropanoyl-CoA
might be rate limiting.
Experiments performed to test the potential of strain
EbN1 to co-metabolize 3-phenylpropanoids that do
not support growth indicated a high substrate
specificity of the involved enzymes. The capacity of
strain EbN1 for lignin monomer degradation is of
ecophysiological relevance, since it could potentially
contribute to the formation and fate of dissolved
organic matter in freshwater and soil environments.
HO
COO -
COSCoA
O
COSCoA COSCoA
COSCoA
COSCoA
+ Acetyl-CoA
Fig. 1. Simplified pathway of oxidation of
hydrocinnamic and cinnamic acid to benzoic acid in
strain EbN1.
References
[1] Boerjan, W., Ralph, J., Baucher, M., 2003. Annu Rev
Plant Biol 54, 519-546.
[2] Dixon, R.A., Paiva, N.L., 1995. The Plant Cell 7, 1085-
1097.
[3] Rabus, R., Widdel, F., 1995. Arch Microbiol 163, 96-103.
[4] Wöhlbrand, L., Wilkes, H., Halder, T., Rabus, R., 2008. J
Bacteriol 190, 5699-5709.
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