Biology Reference
In-Depth Information
5.3. Anaerobic
p -Ethylphenol
Degradation
Inspired by metabolic network proteomics (see below)
p
-ethylphenol
and related aromatic compounds were recently discovered as new
anaerobic growth substrates of
A
.
aromaticum
EbN1. Integrating
identifi cation of
p
-ethylphenol-specifi c proteins (2D DIGE-directed)
and metabolites (GC-MS) allowed proposing a degradation path-
way analogous to that for ethylbenzene: hydroxylation and dehydro-
genation of the methylene carbon, terminal carboxylation, thiolytic
removal of acetyl-CoA, and additionally reductive dehydroxylation
to benzoyl-CoA. The coding genes for
p
-ethylphenol degradation
are organized in a single 15-kb operon-like structure, which is prob-
ably regulated by a single
54
-dependent sensor/regulator. The
sharply demarcated protein profi les of
p
-ethylphenol- vs. ethylben-
zene-adapted cells refl ect a strict sensory distinction between these
two structurally similar compounds. Notably, previous genome annota-
tion could not assign this gene cluster to the catabolic functions subse-
quently inferred by proteomics. In addition, co-regulated proteins
of currently unknown function (e.g., EbA329) were suggested to
represent a novel effl ux system possibly involved in
p
-ethylphenol-
specifi c solvent stress response and related to other aromatic solvent-
induced proteins of
A
.
aromaticum
EbN1 (
56
).
σ
5.4. Anaerobic
Phenylpropanoid
Degradation
Cinnamate and hydrocinnamate (
trans
-3-phenylacrylate and
3-phenylpropionate) as well as their hydroxylated derivatives
p
-coumarate (4-hydroxycinnamate) and 3-(4-hydroxyphenyl)
propionate represent building blocks of lignin and are recently
discovered substrates for anaerobic growth of
A
.
aromaticum
EbN1. 2D DIGE analysis of benzoate-
vs
. cinnamate-, hydrocinna-
mate-,
p
-coumarate-, and 3-(4-hydroxyphenyl)propionate-grown
cells revealed the specifi c upregulation of the same set of protein
spots (up to 44-fold), most likely involved in the
-oxidation of
all four phenylpropanoids to benzoyl-CoA, as supported by metab-
olite analysis. The coding genes are organized in an operon-like
structure (
ebA5316
through
ebA5320
) and could previously not
be assigned to defi ned substrate specifi cities (Trautwein and Rabus,
unpublished).
β
The genome sequence of
A
.
aromaticum
EbN1 predicted multiple
interconnected pathways for anaerobic aromatic compound degra-
dation controlled by a fi ne-tuned regulatory network (
25
). To
assess the genome-wide metabolic and regulatory predictions, a
comprehensive 2D DIGE-based analysis (285 digital gel images
containing in each case 1,047-1,548 detected protein spots) across
22 different substrate and redox conditions was conducted (
57
).
In total, 354 different proteins were identifi ed. The identifi ed
members of the “constitutive” subproteome (core proteome)
comprised 155 proteins displaying low average abundance fold-
changes of ~|1.3|. The “regulated” subproteomes (abundance
fold-changes >|2.5|) collectively contained 199 proteins, which
5.5. Metabolic
Network
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