Biology Reference
In-Depth Information
4.
Phaeobacter
gallaeciensis
DSM
17395:
Heterotrophic
Marine
Roseobacter
The
Roseobacter
clade belongs to the
Alphaproteobacteria
and
covers all major marine habitats: coastal and open ocean waters,
phytoplankton and algal blooms, marine snow, sediments, biofi lms,
and surfaces of marine plants and invertebrates. In open ocean
waters, roseobacters can account for up to 25% of all detected
bacterial phylotypes. The
Roseobacter
clade harbors a wide range of
metabolic capacities, including heterotrophy, aromatic compound
degradation, CO oxidation, aerobic anoxygenic photosynthesis,
and secondary metabolite production. Thus, the
Roseobacter
clade
represents a major lineage of marine bacteria (
43-45
). Recent
comparison of genomes of 32 roseobacter isolates provides a fi rst
comprehensive perspective of patterns in genome features and dis-
tributions of genes and pathways (
46
).
Phaeobacter gallaeciensis
DSM 17395 is an aerobic versatile heterotroph, utilizing a wide
range of carbohydrates and amino acids, and producing the antibi-
otic tropodithietic acid (
47
).
4.1. Background
4.2. Growth Phase-
Dependent Regulation
of Central Metabolism
Global protein (2D DIGE) and metabolite (GC-MS) profi les
were determined at fi ve different time points during growth of
P
.
gallaeciensis
DSM 17395 with glucose. Among the identifi ed
215 proteins and 101 metabolites, 60 proteins and 87 metabolites
displayed changed abundances upon entry into stationary growth
phase. Glucose oxidation apparently proceeds via the Entner-
Doudoroff (ED) pathway, since (1) the key enzyme of the Embden-
Meyerhoff-Parnass pathway (phosphofructokinase, PFK) is not
encoded in the genome and (2) 2-keto-3-desoxygluconate as key
metabolite of the ED pathway and the respective enzymes were
detected. Comparative genomics verifi ed this metabolic trait also
in the majority of other genome-sequenced roseobacters. Upon
entry into stationary growth phase due to glucose depletion,
sulfur assimilation (incl. cysteine biosynthesis) and parts of cell
envelope synthesis (e.g., 1-monooleoylglycerol) were downregu-
lated, while cadaverine formation was upregulated. In contrast,
proteins and metabolites of the ED pathway, pyruvate oxidation,
and TCA cycle remained essentially unchanged, pointing to a
metabolic “standby” modus as an ecophysiological adaptation
strategy. This “standby” and the absence of an
rpoS
gene demon-
strated that stationary phase response of
P
.
gallaeciensis
DSM
17395 differs fundamentally from that of standard organisms such
as
Escherichia coli
(
48
). Glucose breakdown via the ED pathway in
the roseobacters
P
.
gallaeciensis
DSM 17395 and
Dinoroseobacter
shibae
were confi rmed by fl ux analysis (
49
).
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