Biology Reference
In-Depth Information
generation from aerobic carbohydrate oxidation and transition
between planktonic (free-living swarmer cells) and particle-associated
(attached via holdfast substances at the cell pole to nutrient-rich
marine snow) states.
Considering the nutritional specialization of
R
.
baltica
SH1, archi-
tecture and regulation of peripheral and central pathways for
carbohydrate utilization were investigated (Fig.
4a
) (
41
). Almost
all enzymes (25 out of 32 predicted) of glycolysis, tricarboxylic
acid (TCA) cycle, and oxidative branch of the pentose phosphate
cycle were identifi ed. They displayed rather constant fold-changes
of protein abundances (<|1.5|) across all eight applied substrate
conditions (ribose, xylose, glucose, lactose,
N
-acetylglucosamine,
melibiose, maltose, and raffi nose), agreeing with constant in vitro
activities of six selected enzymes. Most of the 22 upregulated
protein species were either dehydrogenases/oxidoreductases of
unknown substrate specifi cities or proteins of unknown function,
which are unique for
R
.
baltica
SH1. This pointed to thus far
unknown routes for peripheral carbohydrate catabolism (Fig.
4b, c
).
The coding genes of many substrate-specifi cally co-regulated
proteins are not organized in clusters on the chromosome, demand-
ing special regulatory processes.
3.2. Carbohydrate
Metabolism
Microscopic analyses indicated motile single swarmer cells of
R
.
baltica
SH1 to dominate during linear growth phase, while
rosette-like cell aggregates were more abundant during stationary
growth phase. Under standard conditions, entry into stationary
growth phase resulted from carbon source (glucose) depletion.
Based on these observations, 2D DIGE was applied at different
time points distributed from early linear to late stationary growth
phase (41-432 h of incubation). The goal was to defi ne protein
signatures of cells representing different morphotypes and stages
in cell cycle, or refl ecting adaptation to nutrient limitation (
42
).
The number of regulated protein spots (fold-changes in protein
abundance >|2|) increased from early (10 spots) to late stationary
growth phase (179 spots), with fold-changes reaching maximal
values of 40. The regulated protein spots represented 98 different
protein species. TCA cycle and oxidative pentose phosphate cycle
were oppositely regulated, while several enzymes of amino acid
biosynthesis were downregulated and the alternative sigma factor
3.3. Growth Phase-
Dependent Regulation
σ
H
upregulated in stationary growth phase. Interestingly, 26 and
10 proteins of unknown function were specifi cally regulated in
the stationary growth phase and during growth on solid surface
(agar plates), respectively. This group of proteins could harbor
promising candidates for the development of the different
R
.
baltica
SH1 morphotypes, i.e., swarmer cells and rosettes.
Search WWH ::
Custom Search