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1.
P. Schmitt C. Couvreur J. F. Cavin H. Prévost Ch. Diviès 《Applied microbiology and biotechnology》1988,29(5):430-436
Summary The effects of pH, temperature and concentration of citrate were investigated to achieve an optimal production of diacetyl, acetoin and C2 compounds such as acetaldehyde, acetate and ethanol for free and immobilized cells. The critical conditions of culture, 22°C, pH 4.8, increased the production of C4 compounds (diacetyl, acetoin, 2, 3 butylene glycol), C2 compounds (acetaldehyde, ethanol, acetate) and formate. A higher yield of C2 and C4 compounds was observed for the immobilized cells than for the free cells in continuous culture. At 75 mMol/l of citrate, the citrate bioconversion yield was 42.8% and 80% for free and immobilized cells, respectively. This paper discusses citrate and lactose utilization and NADH2 part on diacetyl reduction. 相似文献
2.
Since glucose can be oxidized but not assimilated by Acinetobacter calcoaceticus 69-V the question arose whether energy generated by glucose oxidation can help incorporate carbon from heterotrophic substrates and, if so, what the efficiency of ATP production is like. For this reason this species was grown in the chemostat on acetate. After having reached steady state conditions an increasing concentration of glucose was added. This led to an increase in the biomass level from about 0.4 g/g for growth on acetate alone to 0.6–0.65 g/g in the presence of glucose, independently of either the growth rate or the steepness of the glucose gradient used. This upper value approximates about the limit of the carbon conversion efficiency calculated for non-glycolytic substrates. Glucose was almost exclusively oxidized to gluconic acid, 2- and 5-ketogluconates, and pentose 5-phosphates were found only in traces. These results demonstrate that glucose functions as an additional energy source in Acinetobacter calcoaceticus 69-V. From the transient behaviour of biomass increase and the mixing proportion at which the maximum growth yield on acetate in the presence of glucose was obtained it followed that two mol of ATP must have been generated per mol of glucose oxidized. This property is discussed in terms of coupling glucose dehydrogenase with the respiratory chain.Abbreviations
G
ox
glucose oxidized to gluconic acid
-
G
t
amount of glucose necessary for complete substitution of S
d
-
S
o
inlet concentration of the limiting carbon substrate
-
S
a and S
d
assimilated and dissimilated part respectively of the carbon substrate
- PQQ
pyrrolo-quinoline-quinone
-
V
ATP
Ac
ATP gain from complete oxidation to CO2 of acetate (P/O=2)
-
V
ATP
Glc
ATP gain from oxidation of glucose to gluconic acid 相似文献
3.
ATP formation associated with fumarate and nitrate reduction in growing cultures of Veillonella alcalescens 总被引:1,自引:0,他引:1
Wytske de Vries Theresia R. M. Rietveld-Struijk A. H. Stouthamer 《Antonie van Leeuwenhoek》1977,43(2):153-167
Molar growth yields, fermentation balances and enzyme activities were measured in Veillonella alcalescens grown anaerobically with different substrates in the absence or presence of fumarate or nitrate. The molar growth yields on malate (14.3 g dry wt bacteria/mole substrate) and citrate (19.3) were higher than that on lactate (8.6). The molar growth yield on lactate was increased to 15.5 or 19.8 by the addition of fumarate or nitrate, respectively, to the growth medium, and the molar growth yield on citrate was increased to 25.3 by addition of nitrate. Active growth yield was 25.5. From fermentation balances and fermentation systems similar YATP values (g dry wt bacteria/mole ATP) were calculated for all substrates or mixtures of substrates assuming that one mole of ATP is generated at the electron transport from pyruvate, NADH and NADPH to nitrate or fumarate whereas ATP is not produced in the electron transport from lactate to fumarate or nitrate, and, therefore, this assumption was considered to reflect the actual situation. The mean YATP value at a doubling time of 1 h was 16.5 g dry wt bacteria/mole ATP for growth without an added hydrogen acceptor, 14.4 for growth with fumarate, and 14.2 for growth with nitrate. 相似文献
4.
The citrate metabolism of Lactobacillus helveticus ATCC 15807 was studied under controlled-pH fermentations at pH 4.5 and pH 6.2. The micro-organism was able to co-metabolize citrate and lactose at both pH from the beginning of growth, which enhanced the rate of lactose consumption and lactic acid production, compared with cultures without citrate. The effect of citrate on cell growth was dependent on the balance between the ratio of dissociated to non-dissociated forms of the acetic acid produced and the extra ATP gained by the cells, both facts related to the citrate metabolism. The citrate catabolism determined a change in the fermentation pattern of L. helveticus ATCC 15807 from homolactic to a mixed-acid profile, regardless of the external pH. Within this new fermentation pattern, acetate was the major product formed (13–20 mM), followed by succinate (2.4–3.7 mM), while acetoine, dyacetile or butanediol were not detected. The mixed-acid profile displayed by L. helveticus ATCC 15807 was linked to NADH2 oxidase activity rather than the acetate kinase enzyme. 相似文献
5.
A scheme for lysine biosynthesis using variants of the Brevibacterium flavum intermediary metabolite synthesis is discussed. The main precursor of lysine that we are concerned with here is oxalacetate, which can be synthesized through the TCA or glyoxylate cycles or by carboxylation of PEP. Material energy balances for the main pathways of lysine biosynthesis from glucose and acetate have been formulated. Energy consumption, in the from of ATP – PATP (number of mol ATP consumed/1 mol lysine synthesized), was calculated for the main pathways of lysine biosynthesis. Theoretical conversion yields Ypmax (g product/g substrate) were estimated. Experimental data were presented concerning the increase of Yp by means of metabolism regulation: (a) by TCA-and glyoxylate-cycle enzyme induction; (b) by maintaining PEP carboxylase activity; (c) by eliminating by-product synthesis. 相似文献
6.
Thauera selenatis was grown anaerobically in minimal medium with either selenate or nitrate as the terminal electron acceptor and acetate as the carbon source and electron donor. The molar cell protein yields, YM-protein (selenate) and YM-protein (nitrate), were found to be 7.8 g cell protein/mol selenite formed and 7.5 g cell protein/mol nitrite formed, respectively. These values represent YM values of 57 and 55 g (dry weight)/mol acetate when selenate or nitrate was the electron acceptor, respectively. Based upon a calculated YATP value of 10.0 g (dry weight) cells/mol ATP, for growth on acetate in inorganic salts, growth with selenate as the terminal electron acceptor theoretically yielded 5.7 ATP/acetate oxidized, and 5.5 ATP when nitrate was the terminal electron acceptor. The results support the conclusion that energy is conserved via electron transport phosphorylation when selenate or nitrate reduction are the terminal electron acceptors during anaerobic growth with acetate. 相似文献
7.
Masayuki Taniguchi Nobuharu Kotani Takeshi Kobayashi 《Applied microbiology and biotechnology》1987,25(5):438-441
Summary High concentration cultivation of Bifidobacterium longum in a fermenter with cross-flow filtration using a ceramic filter is described. Continuous cross-flow filtration allowed complete recycling of the cells to the fermenter and also continuous separation of inhibitory metabolites. The final cell concentration attained in the cultivation was 54.4 g dry wt./l; this was seven times as high as that without cross-flow filtration. The time course of the cultivation with cross-flow filtration was predicted, based on the assumption that the specific growth rate can be expressed only as a function of concentrations of metabolites (acetate and lactate) in a culture broth.Nomenclature
D
dilution rate (h-1)
-
m
maintenance coefficient (h-1)
-
OD
570
optimal density at 570 nm
-
P
A
acetate concentration (g/l)
-
P
A0
initial acetate concentration (g/l)
-
P
L
lactate concentration (g/l)
-
P
L0
initial lactate concentration (g/l)
-
S
lactose (substrate) concentration (g/l)
-
S
0
initial lactose (substrate) concentration (g/l)
-
t
cultivation time (h)
-
Y
x/s
growth yield (g/g)
-
X
dry cell concentration (g/l)
-
X
0
initial dry cell concentration (g/l)
-
constant
-
constant 相似文献
8.
Eric Giraud Bertrand Lelong Maurice Raimbault 《Applied microbiology and biotechnology》1991,36(1):96-99
Summary Fermentation yields of Lactobacillus plantarum were measured at controlled pH between 4.0 and 8.0 and initial lactate concentrations of 0–90 g/l. Optimal growth conditions at pH 6.0 without addition of lactate gave a growth rate of 0.57 h–1 and 20 g dry biomass/mol ATP formed (Y
ATP). The pH variations resulted in a decrease in growth rate but the effect on Y
ATPwas insignificant. The addition of lactate to the medium at 0 h resulted in linear decrease in the growth rate of the culture, and all the metabolic activities were completely inhibited at 110 g/l. The Y
ATPand biomass/ substrate yield (Y
X/S) remained fairly steady up to 33 g lactate/l, beyond which both yields decreased considerably.
Offsprint requests to: M. Raimbault 相似文献
9.
Dominik Freikowski Josef Winter Claudia Gallert 《Applied microbiology and biotechnology》2010,88(6):1363-1371
Anaerobic growth of a newly isolated Pseudomonas putida strain WB from an arsenic-contaminated soil in West Bengal, India on glucose, l-lactate, and acetate required the presence of arsenate, which was reduced to arsenite. During aerobic growth in the presence
of arsenite arsenate was formed. Anaerobic growth of P. putida WB on glucose was made possible presumably by the non-energy-conserving arsenate reductase ArsC with energy derived only
from substrate level phosphorylation. Two moles of acetate were generated intermediarily and the reducing equivalents of glycolysis
and pyruvate decarboxylation served for arsenate reduction or were released as H2. Anaerobic growth on acetate and lactate was apparently made possible by arsenate reductase ArrA coupled to respiratory electron chain energy conservation. In the presence of arsenate, both substrates were totally oxidized
to CO2 and H2 with part of the H2 serving for respiratory arsenate reduction to deliver energy for growth. The growth yield for anaerobic glucose degradation
to acetate was Y
Glucose = 20 g/mol, leading to an energy coefficient of Y
ATP = 10 g/mol adenosine-5'-triphosphate (ATP), if the Emden–Meyerhof–Parnas pathway with generation of 2 mol ATP/mol glucose
was used. During growth on lactate and acetate no substrate chain phosphorylation was possible. The energy gain by reduction
of arsenate was Y
Arsenate = 6.9 g/mol, which would be little less than one ATP/mol of arsenate. 相似文献
10.
A theoretical study on the amount of ATP required for synthesis of microbial cell material 总被引:15,自引:0,他引:15
A. H. Stouthamer 《Antonie van Leeuwenhoek》1973,39(1):545-565
The amount of ATP required for the formation of microbial cells growing under various conditions was calculated. It was assumed
that the chemical composition of the cell was the same under all these conditions. The analysis of the chemical composition
of microbial cells of Morowitz (1968) was taken as a base. It was assumed that 4 moles of ATP are required for the incorporation
of one mole of amino acid into protein. The amount of ATP required on account of the instability and frequent regeneration
of messenger RNA was calculated from data in the literature pertaining to the relative rates of synthesis of the various classes
of RNA molecules in the cell. An estimate is given of the amount of ATP required for transport processes. For this purpose
it was assumed that 0.5 mole of ATP is necessary for the uptake of 1 g-ion of potassium or ammonium, and 1 mole of ATP for
the uptake of 1 mole of phosphate, amino acid, acetate, malate etc. The results of the calculations show that from preformed
monomers (glucose, amino acids and nucleic acid bases) 31.9 g cells can be formed per g-mole of ATP when acetyl-CoA is formed
from glucose. When acetyl-CoA cannot be formed from glucose and must be formed from acetate, Y
ATP
MAX
is only 26.4. For growth with glucose and inorganic salts a Y
ATP
MAX
value of 28.8 was found. Addition of amino acids was without effect on Y
ATP
MAX
but addition of nucleic acid bases increased the Y
ATP
MAX
value to that for cells growing with preformed monomers. Under these conditions 15–20% of the total ATP required for cell
formation is used for transport processes. Much lower Y
ATP
MAX
values are found for growth with malate, lactate or acetate and inorganic salts. During growth on these substrates a greater
part of the ATP required for cell formation is used for transport processes. The calculated figures are very close to the
experimental values found.
The interrelations between Y
ATP
MAX
and YATP, the specific growth rate (μ), the maintenance coefficient (me) and the P/O rate are given. From a review of the literature evidence is presented that these parameters may vary under different
growth conditions. It is concluded that in previous studies on the relation between ATP production and formation of cell material
these effects have unjustly been neglected. 相似文献
11.
E. coli is still one of the most commonly used hosts for protein production. However, when it is grown with excess glucose, acetate accumulation occurs. Elevated acetate concentrations have an inhibitory effect on growth rate and recombinant protein yield, and thus elimination of acetate formation is an important aim towards industrial production of recombinant proteins. Here we examine if over-expression of citrate synthase (gltA) or phosphoenolpyruvate carboxylase (ppc) can eliminate acetate production. Knock-out as well as over-expression mutants were constructed and characterized. Knocking out ppc or gltA decreased the maximum cell density by 14% and increased the acetate excretion by 7%, respectively decreased it by 10%. Over-expression of ppc or gltA increased the maximum cell dry weight by 91% and 23%, respectively. No acetate excretion was detected at these increased cell densities (35 and 23 g/l, respectively). 相似文献
12.
Héla Kallel-Mhiri Jean-Marc Engasser André Miclo 《Applied microbiology and biotechnology》1993,40(2-3):201-205
The synthesis of ethyl acetate by Kluyveromyces fragilis on diluted whey permeate was studied. Ethanol, lactose and O2 are the direct precursors for ethyl acetate synthesis by this yeast. Ethyl acetate production is affected by many parameters, particularly the carbon/nitrogen (C/N) ratio, Tween 80 and iron. Ethyl acetate synthesis is optimum for C/N = 45. Tween 80 lowered slightly the level of ethyl acetate whereas iron completely stopped ethyl acetate production. The level of ethanol in the feed, the dissolved O2 (DO) and dilution rate (D) were also optimised. Thus at D = 0.24 h –1, for 4 g/l of ethanol in the feed and 40% DO, the productivity of ethyl acetate was optimal (0.7 g/l per hour).
Correspondence to: A. Miclo 相似文献
13.
Using experimental data from continuous cultures of Clostridium acetobutylicum with and without biomass recycle, relationships between product formation, growth and energetic parameters were explored, developed and tested. For glucose-limited cultures the maintenance models for, the Y
ATP and biomass yield on glucose,
and
were found valid, as well as the following relationships between the butanol (Y
B/G) or butyrate (Y
BE/G) yields and the ATP ratio (R
ATP, an energetic parameter), Y
B/G
=0.82-1.35 R
ATP, Y
BE/G
=0.54 + 1.90 R
ATP. For non-glucose-limited cultures the following correlations were developed, Y
B/G
=0.57-1.07 , Y
B/G
=0.82-1.35 R
ATPATP and similar equations for the ethanol yield. All these expressions are valid with and without biomass recycle, and independently of glucose feed or residual concentrations, biomass and product concentrations. The practical significance of these expressions is also discussed.List of Symbols
D h–1
dilution rate
-
m
e
mol g–1 h–1
maintenance energy coefficient
-
m
G
mol g–1 h–1
maintenance energy coefficient
-
R
biomass recycle ratio, (dimensionless)
-
R
ATP
ATP ratio (eqs.(5), (10) and (11)), (dimensionless)
-
X kg/m3
biomass concentration
-
Y
ATP g biomass per mol ATP
biomass yield on ATP
-
Y
ATP
max
g biomass per mol ATP
maximum Y
ATP
-
Y
A/G mol acetate produced per mol glucose consumed
molar yield of acetate
-
y
an/g
mol acetone produced per mol glucose consumed
molar yield of acetone
-
Y
B/G mol butanol produced per mol glucose consumed
molar yield of butanol
-
y
be/g mol butyrate produced per mol glucose consumed
molar yield of butyrate
-
Y
E/G mol ethanol produced per mol glucose consumed
molar yield of ethanol
-
Y
X/G g biomass per mol glucose consumed
biomass yield on glucose
-
Y
ATP
max
g biomass per mol
maximum Y
X/G glucose consumed
-
h–1
specific growth rate 相似文献
14.
The generation time ofP. mirabilis in defined and in complex medium is shorter in the presence of hydrogen acceptors than in their absence. In the presence
of hydrogen acceptors the molar growth yield for glucose and the acetate production are strongly increased. From the molar
growth yield and the acetate production YATP in defined medium was calculated as 5.5 g/mole, whereas in complex medium a value of 12.6 g/mole was obtained. The molar
growth yield, the acetate production, the amount of hydrogen acceptor reduced and YATP were used to calculate P/2e−ratios for phosphorylation coupled to electron transfer to oxygen, nitrate and tetrathionate as respectively 2.80; 1.48 and
1.23 in defined medium. Under anaerobic conditions in the presence of nitrate or tetrathionate as hydrogen acceptor in complex
medium a bend in the growth curve is observed. In the period of rapid growth the P/2e−ratio for nitrate reduction is of the same magnitude as that in defined medium, however much lower P/2e−ratios are found during the subsequent period of slow growth. The P/2e−ratios for tetrathionate reduction in complex medium for both growth periods are lower than those in defined medium. Most
probably these results indicate that during this period growth and energy production are uncoupled. Under aerobic conditions
in complex medium a constant YO value of 32.2 g/atom O is found during a short period of the growth curve. Afterwards when the cell density increases a steady
decrease of YO is observed. 相似文献
15.
pH affected significantly the growth and the glucose fermentation pattern of Propionibacterium microaerophilum. In neutral conditions (pH 6.5–7.5), growth and glucose fermentation rate (qs) were optimum producing propionate, acetate,
CO2, and formate [which together represented 90% (wt/wt) of the end products], and lactate representing only 10% (wt/wt) of the
end products. In acidic conditions, propionate, acetate, and CO2 represented nearly 100% (wt/wt) of the fermentation end products, whereas in alkaline conditions, a shift of glucose catabolism
toward formate and lactate was observed, lactate representing 50% (wt/wt) of the fermentation end products. The energy cellular
yields (Y
X/ATP), calculated (i) by taking into account extra ATP synthesized through the reduction of fumarate into succinate, was 6.1–7.2
g mol−1. When this extra ATP was omitted, it was 11.9–13.1 g mol−1. The comparison of these values with those of Y
X/ATP in P. acidipropionici and other anaerobic bacteria suggested that P. microaerophilum could not synthesize ATP through the reduction of fumarate into succinate and therefore differed metabolically from P. acidipropionici.
Received: 8 April 2002 / Accepted: 8 May 2002 相似文献
16.
Summary The effects of citrate on diacetyl, acetoin and 2,3-butylene glycol (2,3-BG) production by Leuconostoc mesenteroides subsp. cremoris grown in continuous culture at pH 5.2 were studied. In glucose alone end-product production agreed with the theoretical stoichiometry. In the presence of citrate, lactate and acetate production was higher than the theoretical stoichiometry from glucose. Lactate production was constant when the initial citrate concentration was increased whereas ethanol production strongly decreased. In the absence of citrate, citrate lyase (CL) exhibited weak activity. Diacetyl reductase (DR) and acetoin reductase (AR) exhibited basal activity. When varying citrate concentrations ranging from 10 to 75 mm were added to glucose broth, DR, AR, lactate dehydrogenase, NADH oxidase and alcohol dehydrogenase decreased as the initial citrate concentration increased suggesting that they were partly repressed by citrate. In contrast, CL increased and the specific citrate utilization rate also increased in the same way, indicating no saturation of the first step of citrate metabolism. Acetate kinase (AK) was slightly higher in the presence of citrate and increased when the initial citrate concentration increased. This result was correlated with an increase of acetate from the acetyl phosphate pathway. More ATP was produced in the presence of citrate, which could explain the increase in biomass formation. Citrate bioconversion into diacetyl, acetoin and 2,3-BG increased as the initial citrate increased.
Correspondence to: C. Diviès 相似文献
17.
The objective of this study was to assess fermentation product, growth rate and growth yield responses of Selenomonas ruminantium HD4 to limiting and non-limiting ammonia concentrations. The ammonia half-inhibition constant for S. ruminantium in batch culture was 296 mM. Cells were grown in continuous culture with a defined ascorbate-reduced basal medium containing
either 0.5, 5, 25, 50, 100 or 200 mM NH4Cl and dilution rates were 0.07, 0.14, 0.24 or 0.40 h-1. Ammonia was the growth-limiting nutrient when 0.5 mM NH4Cl was provided and the half-saturation constant was 72 μM. Specific rates of glucose utilization and fermentation acid carbon
formation were highest for 0.5 mM NH4Cl. Lactate production (moles per mole of glucose disappearing) increased at the fastest dilution rate (0.40 h-1) for 5.0 mM NH4Cl while acetate and propionate decreased when compared to slower dilutions (0.07 and 0.14 h-1). Lactate production remained low while acetate and propionate remained high for all dilution rates when NH4Cl concentrations were 25 mM or greater. Yield (Y
Glc and Y
ATP) were nearly doubled when NH4Cl was increased from 0.5 mM (25.1 g cells/mol glucose used and 13.9 g cells/mol ATP produced respectively) to the higher
concentrations. Y
Glc was highest at 25 mM and 50 mM NH4Cl (48.2 cells/mol and 43.1 cells/mol respectively) as was Y
ATP (23.2 cells/mol and 20.8 cells/mol respectively). Y
NH3 was highest at the lowest NH4Cl concentration. The maximal fermentation product formation rate occurred at a growth-limiting ammonia concentration, while
maximal glucose and ATP bacterial yields occurred at non-growth-limiting ammonia concentrations. Given the growth response
of this ruminal bacterium, it is possible that maximization of ruminal bacterial yield may necessitate sacrificing the substrate
degradation rate and vice versa.
Received: 5 December 1995/Received revision: 2 April 1996/Accepted: 22 April 1996 相似文献
18.
The efficiency of oxidative phosphorylation in Pseudomonas oxalaticus during growth on oxalate and formate was estimated by two methods. In the first method the amount of ATP required to synthesize cell material of standard composition was calculated during growth of the organism on either of the two substrates. The [Y
ATP
max
] theor. values thus obtained were 12.5 and 6.5 for oxalate and formate respectively, if the assumption were made that no energy is required for transport of oxalate or carbon dioxide. When active transport of oxalate requiring an energy input equivalent to 1 mole of ATP per mole of oxalate was taken into account, [Y
ATP
max
]theor. for oxalate was 9.4. True Y
ATP
max
values were derived from these data on the assumption that the energy produced in the catabolism of Pseudomonas oxalaticus is used with approximately the same efficiency as in a range of other chemoorganotrophs. P/O ratios were calculated using the equation P/O=Y
O/Y
ATP. The data for Y
O and m
e
required for these calculations were obtained from cultures of Pseudomonas oxalaticus growing on oxalate or formate in carbon-limited continuous cultures. The P/O ratios calculated by this method were, for oxalate, 1.3 (or 1.0 if active transport were ignored), and for formate, 1.7.In the second method the stoicheiometries of the respiration-linked proton translocations with oxalate and formate were measured in washed suspensions of cells grown on the two substrates. The H+/O ratios obtained were 4.3 with oxalate and 3.9 with formate. These data indicate the presence of two functional phosphorylation sites in the electron transport chain of Pseudomonas oxalaticus during growth on both substrates. A comparison of the P/O ratio on oxalate obtained with the two methods indicated that the energy requirement for active transport of oxalate has a major effect on the energy budget of the cell; about 50% of the potentially available energy in oxalate is required for its active transport across the cell membrane. Translocation of formate requires approximately 25% of the energy potentially available in the substrate. These results offer an explanation for the fact that molar growth yields of Pseudomonas oxalaticus on oxalate and formate are not very different.Abbreviations PMS
phenazinemethosulphate
- DCPIP
2,6-dichlorophenolindophenol
- TMPD
N,N,N,N-tetramethyl-1,4-phenylene-diamine dihydrochloride
- SD
standard deviation
- PEP
Phosphoenol-pyruvate 相似文献
19.
Citrate Fermentation by Lactococcus and Leuconostoc spp 总被引:1,自引:0,他引:1
Citrate and lactose fermentation are subject to the same metabolic regulation. In both processes, pyruvate is the key intermediate. Lactococcus lactis subsp. lactis biovar diacetylactis homofermentatively converted pyruvate to lactate at high dilution (growth) rates, low pH, and high lactose concentrations. Mixed-acid fermentation with formate, ethanol, and acetate as products was observed under conditions of lactose limitation in continuous culture at pH values above 6.0. An acetoin/butanediol fermentation with alpha-acetolactate as an intermediate was found upon mild aeration in continuous culture and under conditions of excess pyruvate production from citrate. Leuconostoc spp. showed a limited metabolic flexibility. A typical heterofermentative conversion of lactose was observed under all conditions in both continuous and batch cultures. The pyruvate produced from either lactose or citrate was converted to d-lactate. Citrate utilization was pH dependent in both L. lactis and Leuconostoc spp., with maximum rates observed between pH 5.5 and 6.0. The maximum specific growth rate was slightly stimulated by citrate, in L. lactis and greatly stimulated by citrate in Leuconostoc spp., and the conversion of citrate resulted in increased growth yields on lactose for both L. lactis and Leuconostoc spp. This indicates that energy is conserved during the metabolism of citrate. 相似文献
20.
Growth of Pseudomonas oxalaticus in carbon- and energy-limited continuous cultures with mixtures of acetate and formate resulted in the simultaneous utilization of both substrates at all dilution rates tested. During growth on these mixtures, acetate repressed the synthesis of ribulosebisphosphate carboxylase. The degree of this repression was dependent on the dilution rate and on the ratio of acetate and formate in the medium reservoir. At fixed acetate and formate concentrations in the inflowing medium of 30 and 100 mM, respectively, and dilution rates above 0.10h-1, the severe repression of autotrophic enzymes resulted in a marked increase in bacterial dry weight compared to the growth yield of the organisms on the two substrates separately. Also, at these dilution rates a significant increase in isocitrate lyase activity was observed in the cells as compared to growth on acetate alone. This indicated that under these conditions more acetate was assimilated and less dissimilated since acetate was partly replaced by formate as the energy source. When formate was added to the reservoir of an acetate-limited culture (SR=30 mM), derepression of RuBPCase synthesis was observed at formate concentrations of 50 mM and above. Below this concentration formate only served as an energy source for acetate assimilation; when its concentration was increased above 50 mM a progressively increasing contribution of carbon dioxide fixation to the total carbon assimilation was observed as the activity of RuBPCase in the cells increased. It is concluded that in Pseudomonas oxalaticus the synthesis of enzymes involved in autotrophic carbon dioxide fixation via the Calvin cycle is regulated by a repression/derepression mechanism.Abbreviations RuBPCase
ribulosebisphosphate carboxylase
- PMS
phenazine methosulphate
- DCPIP
2,6-dichlorophenol-indophenol
- FDH
formate dehydrogenase
- SR
concentration of growth-limiting substrate in reservoir 相似文献