Interactions between Glucose and Inorganic Carbon Metabolism in Chlorella vulgaris Strain UAM 1011
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Plant Physiol. (1991) 95, 1150-1155 Received for publication August 1, 1990
0032-0889/91/95/1150/06/$01 .00/0 Accepted December 7, 1990
Interactions between Glucose and Inorganic Carbon
Metabolism in Chlorella vulgaris Strain UAM 1011
Flor Martinez* and Maria Isabel Orus
Departamento de Biologia, Facultad de Ciencias, Universidad Aut6noma de Madrid, 28049 Madrid, Spain
ABSTRACT located in Aranjuez (Spain). This strain has been incorporated
Chlorella vulgaris strain UAM 101 has been isolated from the to the Gottingen University Collection of Algae with the
effluent of a sugar refinery. This alga requires glucose to achieve number SAG 9.88.
maximal growth rate even under light saturating conditions. The
growth rate of cultures grown on light + CO2 + glucose (3.16 per Culture Conditions
day) reaches the sum of those grown on light + CO2 (1.95 per
day) and on dark + glucose (1.20 per day). Unlike other Chlorella Axenic batch cultures were grown in 0.5 L flasks containing
strains, uptake of glucose (about 2 micromoles per milligram dry 200 mL of Rodriguez-L6pez A medium (16), at 25°C under
weight per hour) was induced to the same extent in the light and continuous light (or darkness) and shaking, for 48 or 72 h.
dark and was not photosensitive. The rate of dark respiration Initial cell density was 50 ug dry weight- mL-'. Except when
was not affected by light and was strongly stimulated by the otherwise indicated, light intensity during growth was 150
presence of glucose (up to about 40% in 4 hours). The rate of ,uE* m-2 . s- since preliminary experiments had demonstrated
photosynthetic 02 evolution was measured as a function of the
CO2 concentration. These experiments were conducted with cells that this intensity was saturating for the growth of this alga.
which experienced different concentrations of CO2 or glucose Cells grown without added C,2 were grown without supple-
during growth. The maximal photosynthetic rate was inhibited mentary aeration. Where indicated, the cultures were bubbled
severely by growing the cells in the presence of glucose. A rather with either air or 2% (v/v) CO2 in air. For heterotrophic
small difference in the apparent photosynthetic affinity for extra- cultures, the cells were provided with 28 mm glucose. Routine
cellular inorganic carbon (from 10-30 micromolar) was found checkings indicated that glucose depletion did not occur
between cells grown under low and high CO2. Growth with glucose before 72 h.
induced a reduction in the apparent affinity (45 micromolar) even
though cells had not been provided with CO2. Experiments per-
formed at different pH values indicate CO2 as the major carbon Growth Measurements
species taken from the medium by Chlorella vulgaris UAM 101. Dry weight was determined following centrifugation and
drying at 80°C for 20 h. Because the concentration of Chl was
modified during growth with glucose, we have preferred to
report the results on a dry weight basis so as to avoid the bias
of the data if referred to pigment content. The Chl content
We (9) have previously described the heterotrophic poten- was approximately 2% in glucose-grown cells and 3% in cells
tial of the algal population from a sugar refinery wastewater grown on inorganic media. Growth rates (,u) were determined
environment. The most abundant alga in this habitat, Chlo- according to the formula (22)
rella vulgaris UAM 101, exhibited a relatively low rate of
growth when cultured photoautotrophically. Its growth rate, ln x2 - ln xi
however, was strongly stimulated when the medium was t2tl
supplemented with some of the organic compounds normally where xi and x2 are the dry weight of cells at the beginning
present in its habitat. and at the end of the logarithmic phase of growth, which
The present paper reports the effect of light on the growth extended approximately from 18 to 48 h. Cultures were
ofthis strain, as well as special characteristics of glucose uptake examined every day under the light microscope for bacterial
and photosynthetic and respiratory performance in light that contamination.
are related to the glucose stimulation of growth.
MATERIALS AND METHODS Glucose Utilization from the Medium
Organism Cells were harvested by centrifugation, washed three times,
and resuspended in fresh medium supplemented with 2 mM
Chlorella vulgaris UAM 101 is a wild strain that we have glucose to a final cell concentration of 0.2 mg dry weight.
isolated from the wastewater effluent of a sugar refinery mL-' (preliminary experiments indicated that the rate of
' This research was supported by a grant from the Comision 2Abbreviations: Ci, inorganic carbon; RuP2, ribulose- 1,5-bisphos-
Asesora de Investigacion Cientifica y Tecnica. phate; A, growth rate (d-'); AOA, aminooxyacetic acid.
1150
Downloaded from www.plantphysiol.org on September 28, 2015 - Published by www.plant.org
Copyright © 1991 American Society of Plant Biologists. All rights reserved.PHYSIOLOGICAL ADAPTATIONS IN AN HETEROTROPHIC CHLORELLA 1151
glucose uptake in induced cells is saturated in the presence of the medium. Cells were harvested by centrifugation, washed
2 mm glucose). The cells were either illuminated (300 ME three times in 50 mM Tricine-NaOH (pH 8.0) and resus-
m-2-s' white light) or kept in the dark in a 25°C water pended in this buffer to a final density of 1 mg dry weight-
shaking bath. Aliquots were withdrawn where indicated and mL-' in the presence of 2 mm AOA (an inhibitor of glycolate
the glucose remaining in the medium was determined, ac- dehydrogenase [8]). This buffer had also been made CO2 free
cording to the method of Somogyi (17), after short centrifu- as described above. All the samples were held without Ci (or
gation to remove the cells. The rates of glucose removal from any carbon source) during the assay. Glucose was not added
the medium were calculated from the linear range of uptake. to the assay medium since the latter interferes with the deter-
The assays were made under sterile conditions. mination of glycolate. After 15 min of dark preincubation the
cell suspensions were illuminated (300 ME M-2. s-' white
Oxygen Exchange light) for 30 min in a shaking bath at 25°C. The amount of
The cultures were harvested by centrifugation and washed glycolate present in the medium was determined according to
three times in either 20 mM Hepes-NaOH (pH 8.0) or 20 mM Calkins (3), after short centrifugation to remove the cells.
Mes-NaOH (pH 6.2). These buffers were freshly prepared for
every experiment and made CO2 free by bubbling with N2 for RESULTS AND DISCUSSION
several hours. The cell suspensions were placed in a water- Growth Rates of C. vulgaris UAM 101 under
jacketed transparent cylinder equipped with a Clark-type Different Conditions
oxygen electrode (Rank Bros., England) under 300 ME. m-2 _
s- 'white light, and the rates of 02 evolution, in the presence The growth rate of C. vulgaris UAM 101 was strongly
of different concentrations of Ci, were measured according to affected by the presence of glucose, C02, and light intensity
Kaplan and Berry (6). The cell densities used in this part of (Table I). As expected, when the cells were not supplemented
the study corresponded to about 0.1 mg dry weight mL-'. In with Ci or glucose, raising the light intensity from 30 to 150
the case of cultures supplemented with glucose, the latter was ME* m-2 * s-' had no effect on their growth rate. On the other
omitted from the medium in the O2 electrode, since it was hand, in the presence of glucose, the light intensity affected
not possible to reach O2 compensation point in the presence the growth rate strongly, indicating that the metabolism of
of low extracellular Ci (prior to the addition of CQ) due to the glucose and the cell's ability to utilize this organic source was
very high respiratory activity. stimulated by light.
In some experiments, the O2 exchanged was recorded with As in the case of other green algae, supplementing the cell
the same equipment but the sample preparation was different. culture with 2% CO2 stimulated their growth (Table I).
Cells grown without glucose were collected at 24 h and Though the photosynthetic rate was most probably saturated
resuspended in fresh culture medium without or with glucose in the presence of 2% C02, the addition of glucose led to a
to a final cell density of 0.1 mg dry weight. mL-' in 100 mL significant stimulation ofthe growth rate. Actually, the growth
flasks and incubated in the same conditions as culture flasks. rates of C. vulgaris UAM 101 with glucose in light were equal
At the times indicated, an aliquot was withdrawn and used to to or even surpassed the sum of those of photoautotrophic
record dark 02 uptake and 02 evolution. Another aliquot was (light without glucose) and heterotrophic cultures (dark with
incubated with 10 Mm DCMU for 15 min before the measure- glucose) under the different conditions assayed. The fact that
ments. After every determination A600 nm of the sample was the photosynthetic and the respiratory components were ad-
measured and the dry weight concentration calculated from ditive was most surprising, because in green algae organic
a regression line previously performed. Aseptic conditions
were kept during incubation and sampling.
compounds do not contribute to algal growth when light is
saturating. Another exception to this rule has been previously
reported ( 13). It was clear that the photosynthetic rate in this
Glycolate Excretion strain, which is adapted to grow in the presence of glucose,
The rate by which organic carbon enters the glycolate cannot support maximal growth rate. On the other hand,
pathway was assessed from the rate of glycolate excretion to photosynthesis was required to achieve maximal growth rate
Table I. Effect of Light and C, Source on the Growth Rate of C. vulgaris UAM 101 Without and With Glucose
Initial concentration of glucose was 28 mm. Data are means of three experiments with duplicate cultures ± SD.
Growth Conditions Growth Rates (A)
/l(+GIc/+Light)
Ci source Light intensity u(-Glc) g(+Glc)
,g(-Glc/+Light) + u(+GIc/-Light)
AE *m-2 S -1d- d-
Without added Ci Dark 1.08 ± 0.01
30 0.82 ± 0.07 1.90 ± 0.04 1.00
150 0.85 ± 0.02 2.48 ± 0.09 1.28
Air bubbled Dark 1.20 ± 0.05
150 1.11 ±0.05 2.54±0.10 1.10
2% C02-air 150 1.95 ± 0.09 3.16 ± 0.07 1.00
Downloaded from www.plantphysiol.org on September 28, 2015 - Published by www.plant.org
Copyright © 1991 American Society of Plant Biologists. All rights reserved.1152 MARTINEZ AND OROS Plant Physiol. Vol. 95, 1991
a lag of approximately 90 min, in the light to the same extent
as in the dark (Fig. 1). Furthermore, it did not appear to be
photosensitive. It is well established that the uptake of glucose
is mediated by a H+-glucose symport system (7). Since the
,uH+, the presumed driving force of glucose uptake, is strongly
affected by light, it is not surprising that the uptake of glucose
-I
E
analogs is faster in the light than in the dark (20). We have,
however, measured the disappearance of glucose from the
0 medium, over a long period of time. In this case, glucose
metabolism rather than uptake might limit the glucose uptake.
E
2 The cells collected after 24 h of light showed the same rate of
glucose uptake (Fig. 1) indicating that in this strain the uptake
of glucose was not photosensitive. Our conclusion that the
rate of glucose utilization in the light and dark was similar
was further supported by the observation that the rate of
respiration in the presence of glucose was similar in the light
and dark (see below).
Time(min) Respiration and Photosynthesis
Figure 1. Glucose uptake from the medium of C. vulgaris UAM 101 Extensive literature has supported the idea that mitochon-
in the presence of light (300 ,IE m2. S1) or darkness. The assays drial respiration is inhibited by light (21), but some studies
were performed either with cells not preincubated with glucose or provided evidence for the operation of respiration in light, at
with cells grown with 28 mM glucose for 24 h, in light (150 IAE. m2. least under certain conditions (10, 21).
s-1) or darkness. Cells were harvested, washed, and resuspended in The strong stimulation of growth rate in the presence of
fresh medium supplemented with 2 mm glucose (zero time).
glucose suggested that this alga was in fact respiring actively
in light. The experiment reported in Table II was planned to
as the rate of growth under 2% CO2 in the presence of glucose check the operation of mitochondrial respiration under the
was faster than in its absence. Our finding that the presence physiological conditions of culture without and with glucose
of glucose stimulates growth even in the presence of 2% C02, so as to explain the effect of the sugar on growth. We wanted
is taken as evidence that the cells were using glucose as an also to know if there was an effect of glucose on photosynthetic
additional carbon source. 02 evolution during growth that would contribute to this
growth enhancement. We measured 02 consumption in light
Glucose Utilization from the Medium in the presence of DCMU to avoid interference with photo-
synthetic 02 evolution. Our data clearly indicate that the rate
The glucose uptake system of C. vulgaris has been studied of 02 consumption is unaffected by light, even in photoau-
intensively. It is induced within 60 to 90 min following the totrophic cultures. This might be useless for a common alga
supply of glucose in darkness (7, 20). Kamiya and Kowallik but is quite advantageous for an alga that lives in a high sugar
(4, 5) have reported that the glucose uptake mechanism was concentration ambient.
light sensitive and, furthermore, that the uptake was inhibited We have observed in independent experiments that the
in the light. However, our finding that the presence of glucose addition of glucose does not affect the respiratory or photo-
stimulated growth even in the presence of 2% CO2 indicated synthetic rates at zero time after the sugar addition but both
that the cells were using glucose as a carbon source in the activities are clearly stimulated at 24 h and up to 72 h in
light. heterotrophic cultures grown with glucose (14).
The glucose uptake system of our strain was induced, after The 90 min lag in the induction of the glucose uptake
Table II. Effect of Glucose on the Rates of Respiration in Light and Dark, and on Photosynthesis in C.
vulgaris UAM 101 Grown Without Added Ci and Without Glucose
Data are means of three experiments with duplicate samples ± SD.
Photosynthetic
Respiratory Rate (02 consumed) Rate (02
Preincubation Time evolved)
in 28 mm Gic
Dark Dark + Ught + Light
10 AmM DCMU 104mM DCMULih
pnol.mg' dry wt*h-1
No preincubation 1.92 ± 0.11 2.08 ± 0.18 1.98 ± 0.12 1.77 ± 0.13
2h 2.08±0.12 2.08±0.09 2.26±0.05 1.66±0.17
4h 2.62 ± 0.10 2.77 ± 0.13 2.77 ± 0.11 1.78 ± 0.13
Downloaded from www.plantphysiol.org on September 28, 2015 - Published by www.plant.org
Copyright © 1991 American Society of Plant Biologists. All rights reserved.PHYSIOLOGICAL ADAPTATIONS IN AN HETEROTROPHIC CHLORELLA 1153
system (Fig. 1) explains the lack of effect of glucose at zero An analysis of the CO2 response curves of photosynthesis,
time and the slight stimulation of respiratory rate after 2 h of net 02 evolution as a function of the extracellular C1 (Fig. 2),
incubation with the sugar. However, respiratory rate was did not exhibit the expected difference between cells grown
noticeably enhanced after 4 h, reflecting the increasing rate in the presence or absence of supplemented CO2 in their
of glucose metabolism after induction of glucose uptake medium (Fig. 2, A and B). As in other green algae (15), cells
ability. grown under low CO2 environment showed a higher apparent
The measurement of 02 evolution in light without DCMU affinity for extracellular C1. However, the difference between
indicated the net rate of 02 photoevolution that remained high- (30 gM) and low- (10 AM) C02-grown cells is much
constant and was not affected by the presence of glucose at smaller than in other species of green algae, where differences
this time (Table II). The net rate of 02 evolution is the are about 10-fold (1, 11). This Chlorella behaves as if the
algebraic sum of gross photosynthetic 02 evolution and res- typical adaptation of microalgae to low CO2 growth, though
piratory 02 consumption. Because the latter increased during smaller, occurred also in high CO2 environment. Cells grown
the exposure to glucose (Table II), we must conclude that the in the presence of glucose as the sole source of carbon (Fig.
apparent constant net 02 evolution indicates that the gross 2C) exhibited a slightly higher apparent photosynthetic Km(Ci)
rate of photosynthesis increased with time to the same extent (45 gM) than that observed in cells grown in the presence of
as did respiration. Whether this reflects an increased level of CO2. These data indicate that the former respond to the C1
cell metabolism or some unknown control mechanism, re- concentration in the same manner as high-CO2 grown cells,
mains to be resolved. even though they were not supplemented with CO2 during
growth. Similar, though not as clear, response has been ob-
Effect of Different Concentrations of Extemal C, on served in the case of Chiamydomonas cells supplemented
Photosynthetic 02 Evolution with acetate (12; Y Marcus, personal communication). It is
We have seen in the above paragraph that under the phys- not clear why the presence of an organic carbon source
iological conditions used in experiments of Table II, the inhibits the process of adaptation to low-CO2 conditions. In
addition of glucose did not affect the net rate but did increase our case we think that most probably this is due to the CO2
the gross rate of photosynthetic 02 evolution. However, the produced from respired glucose acting as an alternative source
experiments conducted to learn ifthe apparent photosynthetic of substrate for the Ci fixation process. This hypothesis is
affinity for extracellular Ci was modified during growth with consistent with the above commented fact that cells grown
the sugar gave somehow confficting results (Fig. 2). The on glucose exhibited a low Vm. when the sugar was omitted
different experimental conditions (specific buffered medium, from the medium for this assay (Fig. 2C). If this is true, this
anoxygenic atmosphere, compensation point) account for the strain would be a very interesting system to study the signal-
different rates recorded. On the other hand, the photosyn- triggering adaptation process to low-CO2 conditions in algae.
thetic Vm. of cells grown with glucose without aeration and Glucose interferes somehow with Ci metabolism regulation
assayed without glucose (Fig. 2C) was strongly decreased in because it inhibits efficient assimilation of exogenous Ci but
comparison to cells grown without glucose, either without permits, under physiological conditions, rates of photosyn-
aeration (Fig. 2A) or bubbled with 2% CO2 in air (Fig. 2B). thesis higher than those recorded for low-CO2 adapted cells.
The latter clearly indicates that the presence of glucose is The extracellular pH had a small effect on the photosyn-
required, not only to stimulate respiration, but also to get thetic Vm. but a considerable effect on the rate of photosyn-
photosynthesis operating at its best. thesis at low Ci and, consequently, on the apparent Km(Ci).
~~~ ~I I I I I --I
A
15 * 0 A
-c
--
312 0 - -,
10 0o -
Ecm
0 5 0.2 0.4 0.6 0.81 .3-
2
:2
E
o 0 I I 1 f 1 4 Io I
0.2 0.4 0.6 0.8 1.8 0.2 0.4 0.6 0.8 2.0 0.2 0.4 0. 6 0.8 I/2. 3
[H COl m M
Figure 2. Rate of 02 evolution in C. vulgaris UAM 101 as a function of the extracellular Ci at two different extracellular pHs. A, Cells grown
without glucose, without aeration; B, cells grown without glucose, with 2% CO2 aeration; C, cells grown with glucose, without aeration. Cells
were harvested, washed, and resuspended in C02-free buffer (20 mm Mes-NaOH [pH 6.2] or 20 mm Hepes-NaOH [pH 8.0]) and 02 photoevolution
rates in the presence of different concentrations of Ci were recorded after reaching the compensation point (the glucose was omitted during the
assays). (-4), pH 6.2; (O- -0), pH 8.0. -
Downloaded from www.plantphysiol.org on September 28, 2015 - Published by www.plant.org
Copyright © 1991 American Society of Plant Biologists. All rights reserved.1154 MARfINEZ AND OROS Plant Physiol. Vol. 95, 1991
The comparison of the Km(Ci) at high and low external pH significant adaptation to low CO2 in these cells is related to
values has been used to investigate the utilization ofthe species this observation.
of Ci utilized by different algae: greater affinity at elevated pH This alga from a high sugar concentration ambient shows
values has been taken as evidence for HC03- use and the two advantageous features for its habitat: glucose uptake is
opposite behavior has been taken as evidence for C02 use (2). not photosensitive and mitochondrial respiration is not af-
In the strain of Chlorella studied in this work, the apparent fected by light. They can explain the excellent response of this
Km(Ci) is increased by sevenfold at pH 8 in comparison to pH strain to the sugar. The somehow anomalous metabolism of
6. These results are consistent with the possibility that C02 is Ci might be a consequence of the dependence on glucose
the major C, species utilized by this alga. Two among the six under natural conditions, though its physiological significance
different strains of Chlorella studied by Miyachi et al. (11) is unclear.
mainly utilized C02, as does C. vulgaris UAM 101. However,
during the last years, most of the work on the C, species taken ACKNOWLEDGMENTS
up from the medium by green algae has been done with
Chiamydomonas reinhardtii and provides evidence of its abil- We wish to thank Prof. A. Kaplan from the Hebrew University of
ity to take up actively either bicarbonate or C02 (19). Jerusalem for many helpful discussions. We thank Prof. U. G. Schlos-
ser from the University of Gottingen, and Prof. E. Kessler from the
University of Erlangen for their help in the identification of our
Glycolate Excretion strain.
The rate of glycolate excretion was measured as an indica-
tion of the photosynthetic/photorespiratory activity of these LITERATURE CITED
cells, grown under four different conditions. We observed 1. Badger MR, Kaplan A, Berry JA (1980) Internal inorganic
only a small difference between the high- and low-C02-grown carbon pool of Chiamydomonas reinhardtii, evidence for a
cells with respect to glycolate excretion (Table III). These data carbon dioxide-concentrating mechanism. Plant Physiol 66:
are consistent with the relatively small difference between the 407-413
apparent photosynthetic affinities, as a function of the two 2. Beardall J (1985) Occurrence and importance of HCO3- utili-
zation in microscopic algae. In WJ Lucas, JA Berry, eds,
growth conditions. If a certain degree of adaptation to low- Inorganic Carbon Uptake by Aquatic Photosynthetic Orga-
C02 occurs in our high-CO2 Chlorella, as our data indicate nisms. American Society of Plant Physiologists, Rockville,
(see comments on Fig. 2), it is logical that their rate of MD, pp 83-96
photorespiration is not as high as that of a typical high-CO2- 3. Calkins VP (1943) Microdetermination of glycolic and oxalic
grown alga. In cells grown in the presence of glucose, glycolate acids. Ind Eng Chem Anal Ed 15: 762-763
4. Kamiya A, Kowallik W (1987) Photoinhibition of glucose uptake
excretion was depressed. The low rate of glycolate excretion in Chlorella. Plant Cell Physiol 28: 611-619
by glucose-grown cells supports the above cited hypothesis 5. Kamiya A, Kowallik W (1987) The inhibitory effect of light on
that CO2 arising from glucose respiration might contribute to proton-coupled hexose uptake in Chlorella. Plant Cell Physiol
photosynthetic Ci fixation. According to current models of C3 28: 621-625
photosynthesis (18), the rate of carboxylation at a given 6. Kaplan A, Berry JA (1981) Glycolate excretion and the oxygen
to carbon dioxide net exchange ratio during photosynthesis in
activity of Rubisco is saturated when the RuP2 binding sites Chlamydomonas reinhardtii. Plant Physiol 67: 229-232
of Rubisco are all occupied. Since the carboxylation and 7. Komor E, Tanner W (1974) The hexose-proton symport system
oxygenation reactions utilize the same pool of RuP2, it might of Chlorella vulgaris. Specificity, stoichiometry and energetics
be of interest to check the activity of Rubisco and the level of of sugar-induced proton uptake. Eur J Biochem 44: 219-223
8. Krampitz LO, Yarris CE (1983) Glycolate formation and excre-
RuP2 as affected by growth in the presence of glucose. Adap- tion by Chlorella pyrenoidosa and Netrium digitus. Plant Phys-
tation to low C02 conditions in green algae has been correlated iol 72: 1084-1087
with the ratios of photosynthesis/photorespiration activities 9. Martinez F, Avendafio MC, Marco E, Orus MI (1987) Algal
( 18) and the possibility should be considered that the lack of population and auxotrophic adaptation in a sugar refinery
wastewater environment. J Gen Appl Microbiol 33: 331-341
10. McCashin BG, Cossins EA, Canvin DT (1988) Dark respiration
during photosynthesis in wheat leaf slices. Plant Physiol 87:
Table Ill. Glycolate Excretion Rates of C. vulgaris UAM 101 Grown 155-161
With Different Carbon Sources 11. Miyachi S, Tsuzuki M, Avramova ST (1983) Utilization modes
of inorganic carbon for photosynthesis in various species of
Cells were harvested by centrifugation and washed three times in Chlorella. Plant Cell Physiol 24: 441-451
50 mm Tricine-NaOH buffer (pH 8.0) prior to the assay. The samples 12. Moroney JV, Kitayama M, Togasaki RT, Tolbert NE (1987)
were held without added C, or glucose during the assay. The rates Evidence for inorganic carbon transport by intact chloroplasts
were determined from the amount of glycolate excreted in 30 min in of Chlamydomonas reinhardtii. Plant Physiol 83: 460-463
the presence of 2 mm AOA. Data are means of five experiments with 13. Ogawa T, Aiba S (1981) Bioenergetic analysis of mixotrophic
duplicate samples ± SD. growth in Chlorella vulgaris and Scenedesmus acutus. Biotech-
Glycolate Excretion nol Bioeng XXIII: 1121-1132
Growth Conditions Rate 14. Orus MI, Martinez F (1991) Suitability of Chlorella vulgaris
UAM 101 for heterotrophic biomass production. Biomass (in
nmo/-mg-' dry wt *h' press)
Without added Ci 124 ± 0.57 15. Raven JA (1985) The CO2 concentrating mechanism. In WJ
Air bubbled 117 ± 4.27 Lucas, JA Berry, eds, Inorganic Carbon Uptake by Aquatic
2% C02-air 93 ± 1.29 Photosynthetic Organisms. American Society of Plant Physiol-
28 mm glucose, without aeration 71 ± 1.40 ogists, Rockville, MD, pp 67-82
16. Rodriguez-Lopez M (1964) Influence of the inoculum and the
Downloaded from www.plantphysiol.org on September 28, 2015 - Published by www.plant.org
Copyright © 1991 American Society of Plant Biologists. All rights reserved.PHYSIOLOGICAL ADAPTATIONS IN AN HETEROTROPHIC CHLORELLA 1155
medium on the growth of Chlorella pyrenoidosa. Nature 203: 20. Tanner W (1969) Light-driven active uptake of 3-O-methylglu-
666-667 cose via an inducible hexose uptake system of Chlorella.
17. Somogyi M (1945) A new reagent for the determination of sugars. Biochem Biophys Res Commun 36: 278-283
J Biol Chem 160: 61-68 21. Turpin DH, Elrifi IR, Birch DG, Weger HG, Holmes JJ (1988)
18. Spalding MH, Portis AR Jr (1985) A model of carbon dioxide Interactions between photosynthesis, respiration, and nitrogen
assimilation in Chlamydomonas reinhardtii. Planta 164: assimilation in microalgae. Can J Bot 66: 2083-2097
308-320 22. Vonshak A, Maske H (1982) Algae: growth techniques and
19. Sultemeyer DF, Miller AG, Espie GS, Fock HP, Canvin DT biomass production. In J Coombs, DO Hall, eds, Techniques
(1989) Active C02 transport by the green alga Chlamydomonas in Bioproductivity and Photosynthesis. Pergamon Press, Ox-
reinhardtii. Plant Physiol 89: 1213-1219 ford, pp 66-77
Downloaded from www.plantphysiol.org on September 28, 2015 - Published by www.plant.org
Copyright © 1991 American Society of Plant Biologists. All rights reserved.You can also read
