Light-induced gene expression of fructose
1,6-bisphosphate aldolase during heterotrophic growth
in a cyanobacterium, Synechocystis sp. PCC 6803
Yosuke Tabei, Katsuhiko Okada, Nobuaki Makita and Mikio Tsuzuki
School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Japan
In photosynthetic organisms, light activates various
signal transduction pathways regulating the growth
rate, the expression of genes involved in various meta-
bolic processes and the activation of enzymes related
to energy processes. In higher plants, various pheno-
mena concerning photogermination, phototropism and
photoperiodism, including flower initiation, are regu-
lated by light as a signal via phytochromes and ⁄ or
other photoreceptors [1,2]. In cyanobacteria, resetting
of the circadian rhythm [3] and phototaxis [4] have
been analyzed at the gene expression level. In the light,
cyanobacteria assimilate CO
2
via the reductive pentose
phosphate pathway using ATP and NAD(P)H gener-
ated through photosynthesis to produce glycogen and
other organic compounds. In the dark, glucose resi-
dues derived from glycogen are catabolized via glycoly-
sis, the oxidative pentose phosphate pathway (OPPP)
and the incomplete tricarboxylic acid cycle, leading to
the production of NAD(P)H and biosynthetic inter-
mediates for maintenance and growth [5,6]. Both
Keywords
cyanobacteria; glucose degradation; light;
signal transduction; Synechocystis
Correspondence

under light pulse LAHG conditions.
Abbreviations
EMSA, electrophoretic mobility shift assay; FBA, fructose 1,6-bisphosphate aldolase; G6PD, glucose 6-phosphate dehydrogenase; GAPDH,
glyceraldehyde 3-phosphate dehydrogenase; GK, glucokinase; HTH, helix-turn-helix; LAHG, light-activated heterotrophic growth; OPPP,
oxidative pentose phosphate pathway; PGI, glucose 6-phosphate isomerase; PK, pyruvate kinase.
FEBS Journal 276 (2009) 187–198 ª 2008 The Authors Journal compilation ª 2008 FEBS 187
metabolic processes occur in the same compartment in
prokaryotic cells [7].
Synechocystis sp. PCC 6803 (hereafter referred to as
Synechocystis), a unicellular cyanobacterium, is a use-
ful model species for research on biological responses
to the environment because its whole genome sequence
has been determined [8] and molecular techniques are
available, including transformation and homologous
recombination. Exhaustive analyses of gene expression
(such as of the transcriptome and proteome) are now
possible for this organism. For example, new insights
into the role of thioredoxin in the regulation of cellular
processes and the function of the cell membrane in
cyanobacteria have been obtained through proteomic
analysis [9]. Moreover, Synechocystis can grow hetero-
trophically on glucose. Light irradiation, however, is
required for heterotrophic growth, which occurs even
with a low light intensity at which photosynthesis can
scarcely proceed. The cells can grow even with occa-
sional light pulses (e.g. for 5 min every 24 h) [10].
Therefore, so far, this phenomenon has been desig-
nated as light-activated heterotrophic growth (LAHG).
Although hik8 and sigE have been reported to be
necessary for LAHG [11,12], the exact mechanism

important. In the present study, we provide clear
evidence of LAHG with cells at the late-linear and
stationary growth phases of photoautotrophic precul-
ture. In addition, we show that, under LAHG condi-
tions FBA, a glycolytic enzyme, is regulated by light
and glucose via sll1330, a putative gene containing a
helix-turn-helix (HTH) DNA-binding motif.
Results
Growth of Synechocystis and its glucose
utilization under heterotrophic growth conditions
Photoautotrophically grown cells at the late-linear
growth phase were cultured heterotrophically with or
without short periods (5 min) of light every 3 h, which
is considered as LAHG in the present study. The cells
grew with approximately 30 and 66 h of doubling time
on culture with or without light pulses, respectively.
They grew to a two-fold higher level with 10 mm glu-
cose (6.0 · 10
8
cellsÆmL
)1
) than with 5 mm glucose in
approximately 1 week (2.8 · 10
8
cellsÆmL
)1
) (Fig. 1).
However, in continuous darkness (dark heterotrophic
conditions), the cells did not grow so much, even in
the presence of either 5 or 10 mm glucose. Without

that soluble protein synthesis continued at a normal
level under LAHG conditions, but not in the dark.
Dependence of LAHG on the cell conditions for
photoautotrophic preculture
The cell conditions for photoautotrophic preculture
greatly affected the subsequent LAHG and heterotro-
phic growth profiles (Fig. 2). The cells harvested at the
Activation of expression of fbaA in Synechocystis Y. Tabei et al.
188 FEBS Journal 276 (2009) 187–198 ª 2008 The Authors Journal compilation ª 2008 FEBS
logarithmic growth phase could grow fast heterotro-
phically either with or without light pulses (Fig. 2B).
By contrast, those harvested at the stationary growth
phase of the preculture scarcely grew, even in the pres-
ence of glucose in the dark (Fig. 2F). Cells harvested
at any phase of the preculture could grow under
LAHG conditions, although the induction period was
longer with a longer preculture period (Fig. 2C–E).
Therefore, the difference in cell growth between
LAHG and dark heterotrophic conditions was obvious
at a late period of culture, such as the late-linear
growth phase, where reactivation of some processes by
light pulses may occur under LAHG conditions. Cells
harvested on day 8 of photoautotrophic preculture
(Fig. 2E) were used for subsequent experiments.
Proteome analysis of cells grown under
photoautotrophic preculture, LAHG and
dark heterotrophic conditions
The compositions of soluble proteins on culture under
LAHG, dark heterotrophic and the respective precul-
ture conditions were analyzed by 2D-PAGE. Under

results suggest that cellular processes and translation
machinery function differently with or without light in
the presence of glucose. AtpB (spot 9), NatB (10), UrtA
(11), RbcL (17) and CpcB (29), formerly regarded as
representing peripheral membrane proteins [24], were
abundant in the soluble fraction of the cells grown under
LAHG conditions. They might have been extracted dur-
ing our sample preparation due to good solubilization,
or the association between the proteins and the
membrane might change with growth conditions.
0
0.5
1
1.5
A
B
02468
Time (days)
Cell concentration (A
730
)
0
2
4
6
8
10
02468
Time (days)
Glucose concentration (mM)

The activity of FBA, which decreased from 88 to
46 unitsÆmg
)1
protein during autotrophic preculture,
was determined for both LAHG and dark heterotro-
phic cultures (Fig. 4). The FBA activity increased
under LAHG conditions, whereas, under dark hetero-
trophic conditions, it remained constant for 4 days
and then decreased gradually. This finding is consistent
with the protein level of FBA, which was increased by
light pulses in the presence of glucose.
Possible enhancement of glucose metabolism
during LAHG
When 5 mmd-[
14
C(U)]glucose was supplied to cells
that had been incubated in continuous darkness with
5mm glucose for 6 days, most of the radioactivity
incorporated was found in phosphate esters and a
slight amount in glutamate at 1 h after the supply of
d-[
14
C(U)]glucose (data not shown). Thus, we pre-
sumed that even the cells cultured in continuous dark-
ness metabolized it to phosphorylated sugars, but to a
lesser extent to other organic compounds.
2D TLC of a cell extract with detection with ninhy-
drin revealed that glutamate was a major amino acid
in cells incubated under both LAHG and dark hetero-
trophic conditions, but that the amount under the

8d
0
0.2
0.4
0.6
0.8
1.0
7d
02468
0
0.2
0.4
0.6
0.8
1.0
5d
02468
0
0.2
0.4
0.6
0.8
1.0
02468
4d
0
0.2
0.4
0.6
0.8

dithiothreitol (Table 2). The activities of glucokinase
(GK; EC 2.7.1.2) and PK were constantly maintained
under the three sets of conditions. The glucose 6-phos-
phate isomerase (PGI; EC 5.3.1.9) and FBA activities
were relatively higher than those of the other enzymes.
The total activity of FBA under LAHG conditions
was higher than the initial level, whereas that under
dark heterotrophic conditions was lower. The activity
of GAPDH was increased by the addition of glucose.
Therefore, we concluded that FBA was enhanced at
both the protein level and with respect to its activity
8
LAHG conditions
kDa
AB
C
E
D
250
75
50
25
p
I
4
Autotrophic conditions
1
3
4
5

Δsll1330 LAHG conditions
Fig. 3. Proteome analyses of the soluble protein fraction of Synechocystis under various conditions. The soluble proteins were extracted
from Synechocystis cultured under photoautotrophic preculture (A), LAHG (B) and dark heterotrophic (C) conditions for 8 days. Equivalent
amounts of proteins were separated by 2D-PAGE and stained with Coomassie brilliant blue. The profile shown in (E) is identical to (B) with
circles and numbers for annotation purposes. The soluble proteins of Dsll1330 cultured under LAHG conditions for 8 days (D) were also
analyzed. The positions of molecular size markers are indicated in kDa on the left. FBA is indicated by an arrow.
Y. Tabei et al. Activation of expression of fbaA in Synechocystis
FEBS Journal 276 (2009) 187–198 ª 2008 The Authors Journal compilation ª 2008 FEBS 191
under LAHG conditions compared to in continuous
darkness. This result is consistent with the enhance-
ment of fbaA gene expression by light pulses in the
presence of glucose [25].
Changes in the transcript level of fbaA during
heterotrophic culture
Figure 5 shows the changes in the mRNA level of
fbaA under LAHG and dark heterotrophic conditions.
Considering that the cells at 0 days in Fig. 5 had been
grown under photoautotrophic conditions, and that
the mRNA level of fbaA increased under LAHG con-
ditions, we deduced that the increase in the mRNA
level of fbaA was induced by both light pulses and
glucose. On the other hand, the mRNA level of fbaA
under dark heterotrophic conditions increased slightly
until 6 days, and then decreased gradually. The level
under the dark heterotrophic conditions was approxi-
mately one-tenth of that under LAHG conditions after
8 days. These results suggested that light irradiation
was required for the expression of fbaA.
Table 1. Proteins were observed under LAHG conditions to a 1.5-fold greater extent than under autotrophic conditions in Synechocystis.
Category ORF Putative gene product

aldolase (FbaA)
18 s
Transport and binding proteins slr0559 Periplasmic binding protein of ABC
transporter for natural amino acids (NatB)
10 s
sll1447 Periplasmic protein, ABC-type urea
transporter system substrate
binding protein (UrtA)
11
sll1450 Nitrate ⁄ nitrite transporter system
substrate binding protein (NrtA)
13
DNA replication, restriction, modification,
recombination, and repair
sll8006 Type I restriction-modification
system S subunit
12 s
sll1868 DNA primase (DnaG) 1
Translation slr1356 30s ribosomal protein S1 (Rps1a) 20 s
sll1261 Elongation factor Ts (Tsf) 26 s
sll1749 50s ribosomal protein L12 (Rpl12) 31
slr1463 Elongation factor (Fus) 2
sll1099 Elongation factor Tu (TufA) 14
Others slr1198 Antioxidant protein 27 s
sll1621 AhpC ⁄ TSA family protein, 28 s
Unidentified 25 s
Unidentified 23
a
Genes enhanced under LAHG conditions to a 1.5-fold greater extent than under dark conditions are indicated (s).
Activation of expression of fbaA in Synechocystis Y. Tabei et al.

stable than its mRNA. In any case, these results, when
taken together with those obtained previously [25],
suggest that one of the reasons for the inability of
LAHG by Dsll1330 is a lack of enhancement of the
protein level of FBA with light pulses in the presence
of glucose.
FBA activity (mU·mg
–1
protein)
100

0 8 6 4 2
80
60
40
20
0
Time (da
y
s)
Fig. 4. The FBA activities of Synechocystis under LAHG and het-
erotrophic conditions in BG-11 containing 5 m
M glucose. Cells were
incubated under LAHG (white bars) and dark heterotrophic (black
bars) conditions for 2, 4, 6 and 8 days (0 days indicates the activity
of FBA on photoautotrophic preculture on day 8). The error bars
represent three separately grown cultures.
Table 2. Glycolytic enzyme activities of cells grown under dark heterotrophic and LAHG conditions for 8 days.
Enzyme ORF
Activity (mUÆmg

was then subjected to northern hybridization with a probe specific
for the fbaA gene. The lower panel shows rRNA stained with ethi-
dium bromide as a control. The data are representative of three
independent experiments.
Y. Tabei et al. Activation of expression of fbaA in Synechocystis
FEBS Journal 276 (2009) 187–198 ª 2008 The Authors Journal compilation ª 2008 FEBS 193
Interaction of the Sll1330 protein with the fbaA pro-
moter region was additionally examined by means of
the electrophoretic mobility shift assay (EMSA) using
DNA fragments of the upstream region of fbaA (see
Fig. S2). The DNA fragment comprising )331 to
)186 bp from the putative transcription start point of
the fbaA gene was found to bind with Sll1330, which
was overexpressed in Escherichia coli (see Fig. S2).
These results suggest that Sll1330 binds to this putative
promoter region of the fbaA gene in PCC 6803 cells.
Discussion
In the present study, the effects of light on heterotro-
phic growth of Synechocystis were precisely investi-
gated. First, we confirmed that Synechocystis could
not grow in complete darkness, as reported previously
[10]. However, the cells at the logarithmic growth
phase could grow heterotrophically even without illu-
mination. This would be because glucose-degrading
machineries were active in the photoautotrophic pre-
culture at relatively early stages. The total FBA activ-
ity in the late-linear growth phase was lower than that
in the exponential growth phase (Table 2). This is
consistent with the fact that the mRNA levels of some
glycolytic genes were suppressed at the stationary

cantly increased by light irradiation in Synechocystis
[30]. Moreover, the DnaK2 protein is one of the abun-
dant soluble proteins, with dnaK gene expression having
0.6
A
B
D
C
0.4
0.2
0
02468
1.5
1.0
0.5
0
02468
1.0
2.0
3.0
0
02
46
8
0.4
0.2
0
02468
Cell concentration (A
730

, in which
sodB gene and SodB protein expression are induced by
continuous light irradiation [33]. Light induction of
putative 30S ribosomal protein S1 (sll1356) and elonga-
tion factor Ts (sll1261), which are involved in transla-
tion processes, suggests that protein synthesis is
enhanced during cell growth under LAHG conditions.
This is supported by the appearance of more spots on
2D-PAGE of cells under LAHG conditions than under
heterotrophic conditions.
In the present study, the expression of GroEL1, Tig
and GreP was also up-regulated under LAHG condi-
tions compared to under both photoautotrophic and
dark heterotrophic conditions. These results suggest
the higher activities of cellular processes (e.g. protein
synthesis and metabolic processes) under LAHG con-
ditions. FbaA, one of the components of the glucose-
metabolism machinery, was also up-regulated by light
under glucose-utilizing conditions. The protein level of
FbaA was high compared to that of other glycolytic
enzymes. The increase in the maximum Fba activity in
8 days (Fig. 4) under LAHG conditions, but not under
dark heterotrophic conditions, suggested the light acti-
vation of Fba synthesis. This is also supported by the
higher content of glutamate in the cells. Therefore,
cells under LAHG conditions may be more active than
without light.
We found also that, in the sll1330 deletion mutant
(Dsll1330), which could not grow heterotrophically
(Fig. 6), the protein level of FbaA was repressed

bated in the dark with 5 min of light irradiation (5 WÆ m
)2
),
eight times a day in the presence of 5 and 10 mm glucose,
whereas the heterotrophic cultures were incubated without
light irradiation in the presence of glucose. Growth and cell
density were followed by measuring the absorption at
730 nm with a spectrophotometer (DU640; Beckman
Coulter, Fullerton, CA, USA). Cell concentrations were
determined with a hemacytometer (Bu
¨
rker-Turk; Erma Opti-
cal Works, Tokyo, Japan). Glucose uptake was assayed by
measurement of the concentration of glucose in the medium
with a glucose CII kit (Wako Pure Chemical Industries,
Osaka, Japan). In the mutant, the wild-type gene for sll1330
was disrupted by the insertion of a spectinomycin resistance
cassette [25].
Determination of intracellular chlorophyll a,
soluble protein and
L-glutamate
Chlorophyll a was measured by the procedure described by
Mackinney [37], with some modifications. Soluble protein
was assayed by measurement of the concentration of a par-
ticular protein with a BCA protein assay reagent kit (Pierce
Biotechnology, Rockford, IL, USA). Cells were harvested
at a certain time, centrifuged, and then disrupted with a
French press at 28 000 p.s.i. The lysate was centrifuged and
the resulting supernatant was used for the measurement
of soluble protein. Intracellular l-glutamate was assayed

at least four matching peptide masses; (b) at least 50% of
the measured masses must match the theoretical masses;
and (c) 0.01% or better mass accuracy.
Assaying enzyme activity
The cells cultivated under LAHG and heterotrophic condi-
tions were harvested by centrifugation. The pellets were
resuspended and then lysed by three passages through a
French press at 28 000 p.s.i., followed by clarification by cen-
trifugation at 35 000 g for 10 min. The enzyme activities
were measured using previously described procedures
[7,21,38] with some modifications. The assay mixtures com-
prised: GK [50 mm Hepes-KOH (pH 8.0), 1 mm dithiothrei-
tol, 10 mm MgCl
2
, 2.5 mm glucose, 5 mm ATP, 0.5 mm
NAD
+
and 5 unitsÆ mL
)1
G6PD]; PGI [50 mm Hepes-KOH
(pH 8.0), 1 mm dithiothreitol, 10 mm MgCl
2
, 1.7 mm
NAD
+
,2mm fructose 6-phosphate and 5 unitsÆmL
)1
G6PD]; PFK [50 mm Hepes-KOH (pH 8.0), 1 mm dith-
iothreitol, 10 m m MgCl
2

)1
PK and 6 unitsÆmL
)1
lactate
dehydrogenase]; and PK [50 mm Hepes-NaOH (pH 7.0),
30 mm MgCl
2
, 0.15 mm NADH, 2.5 mm phosphoenolpyr-
uvate, 1 mm ADP and 2 unitsÆmL
)1
lactate dehydrogenase].
RNA isolation and northern hybridization
Total RNA was extracted and purified by phenol–chloro-
form extraction [39]. For northern hybridization, the DNA
fragments of fbaA were amplified by PCR, using primers
5¢-ATTTCGATCATGCAGGCCG-3¢ and 5¢-GGAAGAAC
CGTGCATTACC-3¢, and labeled with [a-
32
P]dCTP using a
Megaprime labeling kit (Amersham Pharmacia, Piscataway,
NJ, USA). Hybridization signals were detected with a BAS-
2000 bio-imaging analyzer (Fuji Film, Tokyo, Japan).
Expression of the Sll1330 protein in E. coli
Overexpression of Sll1330 was carried out as described pre-
viously [40] with some modification. The sll1330 gene was
cloned from PCC 6803 genomic DNA after PCR amplifica-
tion using specific oligonucleotides. The sll1330 gene was
amplified using primers 1330OX-F (5¢-GTCTAGA
CAT
ATGAATCCAG-3¢), comprising nucleotides )10 to +10

the correction of the English. They are also indebted
to Mr Masato Sasahara, Ms Yuka Katsuki and
Activation of expression of fbaA in Synechocystis Y. Tabei et al.
196 FEBS Journal 276 (2009) 187–198 ª 2008 The Authors Journal compilation ª 2008 FEBS
Ms Miwako Itoh for their experimental support. This
work was supported by Grants-in-Aid from the Minis-
try of Education, Science, Sports and Culture, Japan;
the Promotion and Mutual Aid Corporation for Pri-
vate Schools to M. T.; and a Sasakawa Scientific
Research Grant from the Japan Science Society to
Y. T.
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Supporting information
The following supplementary material is available:
Fig. S1. Amino acid compositions of soluble fractions
of Synechocystis.
Fig. S2. EMSA analysis of Sll1330 and the promoter
region of the fbaA gene.
This supplementary material can be found in the
online version of this article.