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1.
Azotobacter vinelandii strain AVOP (wild type) and an ascorbate- N,N,N,N-tetramethylene- p-phenylenediamine oxidase-negative mutant (AV11) were each grown in O 2-limited chemostat cultures. The results showed that the mutant strain grew and used O 2 less efficiently than the wild-type strain. Respiration rates of membrane particles with NADH or malate as the substrate were similar for each strain. Succinate oxidase activity was about fourfold lower in membrane particles prepared from mutant than from wild-type strain. Cyanide at a concentration that completely inhibited ascorbate-TMPD oxidase activity resulted in a 50% inhibition of NADH oxidase activity in membrane particles of AVOP. These data suggest that the cytochrome o, a
1, oxidase branch of the respiratory chain may be important in the physiology of A. vinelandii under O 2-limiting growth conditions. 相似文献
2.
A mutant of Dunaliella tertiolecta produced by treatment with methyl nitrosoguanidine and designated HL25/8, grew more slowly than the parent strain under all experimental conditions and was conspicuously less tolerant of NaCl. Total photosynthetic activity (C-fixation and O 2 evolution) was less in HL25/8 than in the parent strain and was affected differently by [NaCl] in the two strains. Various growth characteristics indicated that the mutant had a greater need than the parent strain for CO 2 as distinct from HCO
3
–
as a source of carbon. Gaseous CO 2 extended the range of salt tolerance of the mutant. For example, HL25/8 could not sustain growth at 1.02 M NaCl in a conventional buffered medium containing bicarbonate as the sole carbon source but could do so if the medium were sparged with a CO 2/air mixture. The mutant strain has a lower activity of carbonic anhydrase on the cell surface than the parent D. tertiolecta. Moreover, the two strains differ sharply in the responses of their surface carbonic anhydrase activity to salinity of the growth medium. Increasing sodium chloride concentration above 0.17 M raised activity of the enzyme in the parent strain but decreased it in HL25/8. We conclude that the low activity of carbonic anhydrase and its response to salinity can largely, but perhaps not fully, explain the diminished salt tolerance of the mutant. A plate counting method applicable to Dunaliella is described. 相似文献
3.
The cytochrome bc
1 complexes from the nonphotosynthetic strain R126 of Rhodobacter capsulatus and from its revertant MR126 were purified. Between both preparations, no difference could be observed in the stoichiometries of the cytochromes, in their spectral properties, and in their midpoint redox potentials. Both also showed identical polypeptide patterns after electrophoresis on polyacrylamide gels in the presence of sodium dodecylsulfate. The ubiquinol: cytochrome c oxidoreductase activity was strongly inhibited in the complex from the mutant compared to the one from the revertant. So was the oxidant-induced extra reduction of cytochrome b. Both preparations, however, showed an antimycin-induced red shift of cytochrome b, as well as antimycin-sensitive reduction of cytochrome b by ubiquinol. In accordance with a preceding study of chromatophores (Robertson et al. (1986). J. Biol. Chem.
261, 584–591), it is concluded that the mutation affects specifically the ubiquinol oxidizing site, leaving the ubiquinol reducing site unchanged. 相似文献
4.
Summary Two strains of Saccharomyces cerevisiae were used to study the synthesis of superoxide dismutase. One strain (cytochrome c-deficient) contained 5–10% of the normal amounts of total cytochrome c, while the other strain was a wild type. The cytochrome c-deficient mutant had lower specific growth rate, growth yield, and oxygen uptake than the wild type. The superoxide dismutase and catalase activities, in both strains, were significantly lower under anaerobic than under aerobic conditions. Furthermore, under aerobic conditions the mutant contained higher levels of superoxide dismutase than the wild type which may be attributed to the higher intracellular flux of superoxide radicals caused by the cytochrome c deficiency. The mutant also showed a lower level of catalase which was due to glucose repression.Paper Number 10007 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695, U.S.A. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned. 相似文献
5.
An Hg 2+-sensitive mutant strain was isolated from an Hg 2+-tolerant bacterium Pseudomonas oleovorans G-1 strain by mutagenesis with N-methyl- N′-nitro- N-nitrosoguanidine. The Hg 2+-sensitive mutant strain was about 10-times as sensitive to Hg 2+ as the parent strain. Moreover, the mutant strain was considerably more sensitive to Cr 6+ than the parent strain, but it did not show an appreciable change in sensitivity to Cd 2+ and Cu 2+. The mutant strain was considerably more sensitive to antibiotics achromycin, chloramphenicol and streptomycin than the parent strain. A more rigid structure was observed in the cell envelope of the mutant strain than the parent strain under transmission electron microscope. Higher amounts of DNA but less protein and RNA were found in the mutant strain compared to the parent strain. Disc electrophoretic patterns showed some differences in protein bands between the parent and mutant strain. 相似文献
6.
Electron transport of normal and photobleached Anabaena cylindrica was studied using spectral and kinetic analyses of absorbance transients induced by single turnover flashes. Between 500 and 600 nm two positive bands (540 and 566 nm) and two negative bands (515 and 554 nm) were found. Absorbance changes at 515 and 540 nm were partly characterized. None of these absorbance changes represent an electrochromic shift. Absorbance changes at 554 and 566 nm correspond to the oxidation of cytochrome f and the reduction of cytochrome b
563, respectively. We found a very slight 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) sensitivity of cytochrome f in normal cells, while DCMU was completely ineffective for cytochrome f reduction in photobleached cells. The absorbance change of cytochrome b
563 increased, while the absorbance change of cytochrome f was smaller than in normal cells. The increased O 2 evolution in photobleached cells and the negligible electron transport via cytochrome f suggest the participation of other electron acceptor(s) in the electron-transport chain of photobleached Anabaena cylindrica. 相似文献
7.
The reduction of cyctochromes c + c
1 by durohydroquinone and ferrocyanide in electron transport particles (ETP) and intact cytochrome c-depleted beef heart mitochondria has been studied. At least 94% of the ETP are in an inverted orientation. Durohydroquinone reduces 80% of c + c
1 in ETP but less than 20% in mitochondria; sonication of mitochondria allows reduction of cytochromes c + c
1 (80%). Addition of ferrocyanide (effective redox potential +245 mV) to electron transport particles results in 30% reduction of cytochromes c + c
1. Addition of ferrocyanide to intact cytochrome c-depleted mitochondria does not reduce cytochrome c
1; treatment with N,N,N,N-tetramethylphenylenediamine, Triton X-100, or sonic oscillation results in 30% reduction of cytochromes c + c
1. The K
m
value of ferrocyanide oxidase for K-ferrocyanide is pH-dependent in ETP only, increasing with increasing pH. The extent of reduction of cytochrome c
1 is also pH-dependent in ETP only, the extent of reduction increasing with decreasing pH. On the basis of these data cytochrome c
1 is exposed to the matrix face and cytochrome c is exposed to the cytoplasmic face. No redox center other than cytochrome c in the segment between the antimycin site and cytochrome c is exposed on the C-side.Abbreviations Used: MES, 2( N-morpholino)-ethanesulfonic acid; EDTA, ethylenediaminetetraacetic acid; TMPD, N,N,N,N-tetramethylphenylenediamine; ETP, electron transport particles; NAD-NADH, nicotinamide adenine dinucleotide; PMS, phenazine methosulfate. 相似文献
8.
An analysis of resonance Raman scattering data from CO-bound cytochrome c oxidase and from the photodissociated enzyme indicates that histidine may not be coordinated to the iron atom of cytochrome a
3 in the CO-bound form of the enzyme. Instead, the data suggest that either a water molecule or a different amino acid residue occupies the proximal ligand position. From these data, it is postulated that ligand exchange on cytochrome a
3 can occur under physiological conditions. Studies of mutant hemoglobins have demonstrated that tyrosinate binds preferentially to histidine in the ferric forms of the proteins. In cytochrome c oxidase tyrosine residues are located near the histidine residues recently implicated in coordination to cytochrome a
3 (Shapleigh et al., 1992; Hosler et al., this volume). Expanding on these concepts, we propose a model for proton translocation at the O 2-binding site based on proximal ligand exchange between tyrosine and histidine on cytochrome a
3. The pumping steps take place at the level of the peroxy intermediate and at the level of the ferryl intermediate in the catalytic cycle and are thereby consistent with the recent results of Wilkstrom (1989) who found that proton pumping occurs only at these two steps. It is shown that the model may be readily extended to account for the pumping of two protons at each of the steps. 相似文献
9.
The cytochrome bc complexes of the electron transport chain from a wide variety of organisms generate an electrochemical proton gradient which is used for the synthesis of ATP. Proton translocation studies with radiolabeled N,N-dicyclohexylcarbodiimide (DCCD), the well-established carboxyl-modifying reagent, inhibited proton-translocation 50–70% with minimal effect on electron transfer in the cytochrome bc
1 and cytochrome bf complexes reconstituted into liposomes. Subsequent binding studies with cytochrome bc
1 and cytochrome bf complexes indicate that DCCD specifically binds to the subunit b and subunit b
6, respectively, in a time and concentration dependent manner. Further analyses of the results with cyanogen bromide and protease digestion suggest that the probable site of DCCD binding is aspartate 160 of yeast cytochrome b and aspartate 155 or glutamate 166 of spinach cytochrome b
6. Moreover, similar inhibition of proton translocating activity and binding to cytochrome b and cytochrome b
6 were noticed with N-cyclo-N-(4-dimethylamino-napthyl)carbodiimide (NCD-4), a fluorescent analogue of DCCD. The spin-label quenching experiments provide further evidence that the binding site for NCD-4 on helix cd of both cytochrome b and cytochrome b
6 is localized near the surface of the membrane but shielded from the external medium. 相似文献
10.
The oxidation of cytochrome b
561 by ATP was measured in submitochondrial particles inhibited by antimycin. The redox potential of the bulk ( M phase) was controlled by the ratio of fumarate:succinate, and the oxidation of cytochrome b was calculated and expressed as a change in redox potential ( E
h) measured in millivolts. The oxidation of cytochrome b
561 is an energy-driven reaction affected only by the component of the proton motive force. The oxidation (measured in millivolts) is a function of the phosphate potential, reaching a maximal value of 40 mV at GATP<–12 kcal/mole. The maximal measured value of ATP-dependent was 100 mV. Thus only a fraction of the membrane potential effects the redox state of cytochrome b
561. In contrast to the ATP-induced oxidation of cytochrome b
561, cytochrome b
566 is in redox equilibrium with fumarate succinate either in the presence or in the absence of ATP. The selective oxidation of b
561 is explained within the term of the Q cycle as a reflection of on the electron electrochemical potential. The positive electric potential of the C phase causes cytochrome b
566 to act as oxidant with respect to cytochrome b
561. In the presence of antimycin cytochrome b
561 cannot equilibrate with the quinone and undergoes oxidation, while cytochrome b
566 reequilibrates with the quinone and thus regains redox equilibrium with the fumarate succinate redox buffer.Abbreviations used: ETP H, phosphorylating submitochondrial particles; TMPD, N
1
N
1
NN-tetramethyl- p-phenylenediamine; FCCP, carbonylcyanide p-trifluoromethoxyphenylhydrazone; Mes, 2-( N-morpholino) ethanesulfonic acid. 相似文献
11.
Cytochromes c and c
1 are essential components of the mitochondrial respiratory chain. In both cytochromes the heme group is covalently linked to the polypeptide chain via thioether bridges. The location of the two cytochromes is in the intermembrane space; cytochrome c is loosely attached to the surface of the inner mitochondrial membrane, whereas cytochrome c
1 is firmly anchored to the inner membrane. Both cytochrome c and c
1 are encoded by nuclear genes, translated on cytoplasmic ribosomes, and are transported into the mitochondria where they become covalently modified and assembled. Despite the many similarities, the import pathways of cytochrome c and c
1 are drastically different. Cytochrome c
1 is made as a precursor with a complex bipartite presequence. In a first step the precursor is directed across outer and inner membranes to the matrix compartment of the mitochondria where cleavage of the first part of the presequence takes place. In a following step the intermediate-size form is redirected across the inner membrane; heme addition then occurs on the surface of the inner membrane followed by the second processing reaction. The import pathway of cytochrome c is exceptional in practically all aspects, in comparison with the general import pathway into mitochondria. Cytochrome c is synthesized as apocytochrome c without any additional sequence. It is translocated selectively across the outer membrane. Addition of the heme group, catalyzed by cytochrome c heme lyase, is a requirement for transport. In summary, cytochrome c
1 import appears to follow a conservative pathway reflecting features of cytochrome c
1 sorting in prokaryotic cells. In contrast, cytochrome c has invented a rather unique pathway which is essentially non-conservative. 相似文献
12.
Electron transport in the Paracoccus denitrificans respiratory chain system is considerably more rapid when it includes the membrane-bound cytochrome c
552 than with either soluble Paracoccus c
550 or bovine cytochrome c; a pool function for cytochrome c is not necessary. Low concentrations of Paracoccus or bovine cytochrome c stimulate the oxidase activity. This observation could explain the multiphasic Scatchard plots which are obtained. A negatively charged area on the back side of Paracoccus c which is not present in mitochondrial c could be a control mechanism for Paracoccus reactions. Paracoccus oxidase and reductase reactions with bovine c show the same properties as mammalian systems; and this is true of Paracoccus oxidase reactions with its own soluble cytochrome c if added polycation masks the negatively charged area. Evidence for different oxidase and reductase reaction sites on cytochrome c include: (1) stimulation of the oxidase but not reductase by a polycation; (2) differences in the inhibition of the oxidase and reductases by monoclonal antibodies to Paracoccus cytochrome c; and (3) reaction of another bacterial cytochrome c with Paracoccus reductases but not oxidase. Rapid electron transport occurs in cytochrome c-less mutants of Paracoccus, suggesting that the reactions result from collision of diffusing complexes. 相似文献
13.
A comparative study of photosystem II complexes isolated from tobacco ( Nicotiana tabacum L. cv. John William's Broadleaf) which contains normal stacked thylakoid membranes, and from two chlorophyll deficient tobacco mutants (Su/su and Su/su var. Aurea) which have low stacked grana or essentially unstacked thylakoids with occasional membrane doublings, has been carried out. The corresponding photosystem II complexes had an O 2 evolving activity ranging from 290 (for the wild type) to 1100 mol O 2 x mg chlorophyll -1 x h -1 (for the mutant Su/su var. Aurea). The reduced photosynthetic unit size was also obvious in the mangenese and cytochrome b559 content. The photosystem II complex from the wild type contained 4 Mn and 1 cytochrome b559 per 200 to 280 chlorophylls, while the corresponding value for the mutant Su/su var. Aurea was 4 Mn and 1 cytochrome b559 per 35 to 60 chlorophylls. We have also examined the polypeptide composition and show that the photosystem II complex from the wild type consisted of polypeptides of 48, 42, 33, 32, 30, 28, 23, 21, 18, 16 and 10 kDa, while the mutant complex mainly contained the polypeptides of 48, 42, 33, 32, 30, 28 and 10 kDa. In the mutant photosystem II complex the light-harvesting chlorophyll protein (peptide of 28 kDa) was reduced by a factor of 5 to 6 as compared to the wild type. With respect to the peptide composition and the photosynthetic unit size, the Triton-solubilized photosystem II complex from the mutant Su/su var. Aurea was very similar to O 2 evolving photosystem II reaction center core complexes.Abbreviations PS
photosystem
- chl
chlorophyll
- LHCP
light-harvesting chlorophyll a/b protein complex 相似文献
14.
Intracellular concentrations of hexose phosphates, phosphoenolpyruvate, pyruvate, NAD(H) and NADP(H) as well as the protein and poly--hydroxybutyrate (PHB) content were measured in suspensions of autotrophically grown cells of Alcaligenes eutrophus H 16 and compared with those in a mutant unable to synthesize poly--hydroxybutyrate. The parent strain was subjected to successive changes in conditions, and new steady states were rapidly (20 min) attained. When the parent strain was provided with carbon and energy but no nitrogen source, it fixed CO 2 and accumulated large amounts of PHB. When the mutant PHB -4 was exposed to identical conditions, no accumulation of PHB occurred, but pyruvate, malate and citrate were excreted, and a 6-fold accumulation of hexose monophosphate (over the levels in the parent) was observed: in contrast, cofactors in intermediates between fructose-1,6-phosphate and phospho enolpyruvate reached steady state as in the parent strain. When ammonium ion was then supplied, growth started and the metabolite concentrations in the mutant returned to the levels observed in the parent strain. 相似文献
15.
In coenzyme Q-cycles, it is proposed that one electron from the quinol reduces the Rieske iron sulfur center ( E
m280 mV) and the remaining electron on the semiquinone reduces cytochrome b
T ( E
m–60 mV). The E
mfor the two-electron oxidation of the quinol is 60 mV and therefore the reduction of cytochrome b
T by quinol is not favorable. As the stability constant for the dismutation of the semiquinone decreases, the calculated E
mfor the Q/QH couple is lowered to values below the E
mof cytochrome b
T. Contemporary coenzyme Q-cycles are based on the belief that the lower value for the E
mof the Q/QH couple compared to the E
mfor cytochrome b
T means that the semiquinone is a spontaneous reducing agent for the b-cytochrome. The analysis in the paper shows that this is not necessarily so and that neither binding sites nor ionization of the semiquinone per se alters this situation. For a Q-cycle mechanism to function, ad hoc provisions must be made to drive the otherwise unfavorable reduction of cytochrome b
T by the semiquinone or for the simultaneous transfer of both electrons to cytochrome b
T and cytochrome c
1 (or the iron sulfur protein). Q-cycle mechanisms with these additional provisions can explain the observation thus far accumulated. A linear path which is functionally altered by conformational changes may also explain the data. 相似文献
16.
The effects of increasing the heterocyst-to-vegetative cell ratio on the nitrogenase-based photobiological hydrogen production by the filamentous heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 were studied. Using the uptake hydrogenase-disrupted mutant (ΔHup) as the parent, a deletion-insertion mutant (PN1) was created in patN, known to be involved in heterocyst pattern formation and leading to multiple singular heterocysts (MSH) in Nostoc punctiforme strain ATCC 29133. The PN1 strain showed heterocyst differentiation but failed to grow in medium free of combined-nitrogen; however, a spontaneous mutant (PN22) was obtained on prolonged incubation of PN1 liquid cultures and was able to grow robustly on N2. The disruption of patN was confirmed in both PN1 and PN22 by PCR and whole genome resequencing. Under combined-nitrogen limitation, the percentage of heterocysts to total cells in the PN22 filaments was 13–15 and 16–18% under air and 1% CO2-enriched air, respectively, in contrast to the parent ΔHup which formed 6.5–11 and 9.7–13% heterocysts in these conditions. The PN22 strain exhibited a MSH phenotype, normal diazotrophic growth, and higher H2 productivity at high cell concentrations, and was less susceptible to photoinhibition by strong light than the parent ΔHup strain, resulting in greater light energy utilization efficiency in H2 production on a per unit area basis under high light conditions. The increase in MSH frequency shown here appears to be a viable strategy for enhancing H2 productivity by outdoor cultures of cyanobacteria in high-light environments. 相似文献
17.
Paracoccus denitrificans is able to grow on the C 1 compounds methanol and methylamine. These compounds are oxidized to formaldehyde which is subsequently oxidized via formate to carbon dioxide. Biomass is produced by carbon dioxide fixation via the ribulose biphosphate pathway. The first oxidation reaction is catalyzed by the enzymes methanol dehydrogenase and methylamine dehydrogenase, respectively. Both enzymes contain two different subunits in an 22 configuration. The genes encoding the subunits of methanol dehydrogenase ( moxF and moxI) have been isolated and sequenced. They are located in one operon together with two other genes ( moxJ and moxG) in the gene order moxFJGI. The function of the moxJ gene product is not yet known. MoxG codes for a cytochrome c
551i
, which functions as the electron acceptor of methanol dehydrogenase. Both methanol dehydrogenase and methylamine dehydrogenase contain PQQ as a cofactor. These so-called quinoproteins are able to catalyze redox reactions by one-electron steps. The reaction mechanism of this oxidation will be described. Electrons from the oxidation reaction are donated to the electron transport chain at the level of cytochrome c. P. denitrificans is able to synthesize at least 10 different c-type cytochromes. Five could be detected in the periplasm and five have been found in the cytoplasmic membrane. The membrane-bound cytochrome c
1 and cytochrome c
552 and the periplasmic-located cytochrome c
550 are present under all tested growth conditions. The cytochromes c
551i
and c
553i
, present in the periplasm, are only induced in cells grown on methanol, methylamine, or choline. The other c-type cytochromes are mainly detected either under oxygen limited conditions or under anaerobic conditions with nitrate as electron acceptor or under both conditions. An overview including the induction pattern of all P. denitrificans c-type cytochromes will be given. The genes encoding cytochrome c
1, cytochrome c
550, cytochrome c
551i
, and cytochrome c
553i
have been isolated and sequenced. By using site-directed mutagenesis these genes were mutated in the genome. The mutants thus obtained were used to study electron transport during growth on C 1 compounds. This electron transport has also been studied by determining electron transfer rates in in vitro experiments. The exact pathways, however, are not yet fully understood. Electrons from methanol dehydrogenase are donated to cytochrome c
551i
. Further electron transport is either via cytochrome c
550 or cytochrome c
553i
to cytochrome aa
3. However, direct electron transport from cytochrome c
551i
to the terminal oxidase might be possible as well. Electrons from methylamine dehydrogenase are donated to amicyanin and then via cytochrome c
550 to cytochrome aa
3, but other routes are used also. P. denitrificans is studied by several groups by using a genetic approach. Several genes have already been cloned and sequenced and a lot of mutants have been isolated. The development of a host/vector system and several techniques for mutation induction that are used in P. denitrificans genetics will be described. 相似文献
18.
A mutant strain of the bacterium Pseudomonas sp. ATCC 31461 that exhibited elevated production of the polysaccharide gellan on glucose or corn syrup as a carbon source
was isolated. Gellan production by the mutant strain was about twofold higher than its parent strain on glucose or corn syrup
after 48 h of growth, and about 1.4-fold higher after 72 h. An increase in biomass production was not correlated with enhanced
gellan synthesis by the mutant strain. The increased gellan production by the mutant strain on either carbon source resulted
in an increase in its culture medium viscosity and the viscosity of the isolated polysaccharide produced by glucose-grown
cells. No differences in the glucuronic acid content of the polysaccharides produced by the mutant and parent strains were
observed. Journal of Industrial Microbiology & Biotechnology (2002) 29, 185–188 doi:10.1038/sj.jim.7000278
Received 13 February 2002/ Accepted in revised form 20 May 2002 相似文献
19.
Exposure of the exopolysaccharide (EPS)-synthesizing cyanobacterium Nostoc spongiaeforme to Zn 2+ (20 M) transformed the biomass into white debris. However, a few blue–green pin-heads emerged after 2 weeks in the same Zn 2+-containing medium and formed less mucoid microcolonies (1–2 mm) relative to the protruding colonies (2–4 mm) of the parent strain on nutrient agar. One of such survivors (designated as Zn 20) that was stable through 10 successive transfers in Zn 2+-lacking medium has been adopted for further characterization. The parent strain retained almost 88% of the total EPS synthesized, the rest being released into the ambient medium, while for Zn 20, the EPS retained approximated to 74%. Although the Zn 2+-sensitivity of the mutant was comparable with that of the parent (LD 50, 7 M), Zn 2+ uptake was still 5-fold higher in the former (2 g mg –1 biomass dry wt., 20 M, external concentration). Also, both the strains showed insignificant difference in Zn 2+-sorption onto their isolated EPS. The mutant was characterized by having higher cell carbohydrate content (642.8 g mg –1 dry wt.) than its parent (513.6 g). The X-ray diffraction pattern revealed Zn 2+ deposition on EPS from the parent mainly as zinc hypophosphite monohydrate [Zn(H 2PO 2) 2·H 2O], whereas there was a lack of distinct peaks in similar samples from Zn 20, thus confirming the amorphous nature. There was participation in Zn 2+ binding of only COO –, N=O, NO 2, SO 2 groups in the parent while participation of P—O and C=O groups in mutant EPS was evident in IR spectra. The observations suggest that the mutant could be deployed to achieve sustained EPS synthesis, its release and metal sorption/desorption in repeated cycles. 相似文献
20.
Citric acid production from sugar cane molasses by Aspergillus niger NIAB 280 was studied in a batch cultivation process. A maximum of 90 g/L total sugar was utilized in citric acid production
medium. From the parental strain A. niger, mutant strains showing resistance to 2-deoxyglucose in Vogal's medium containing molasses as a carbon source were induced
by γ-irradiation. Among the new series of mutant strains, strain RP7 produced 120 g/L while the parental strain produced 80
g/L citric acid (1.5-fold improvement) from 150 g/L of molasses sugars. The period of citric acid production was shortened
from 10 d for the wild-type strain to 6–7 d for the mutant strain. The efficiency of substrate uptake rate with respect to
total volume substrate consumption rate, Q
s (g per L per h) and specific substrate consumption rate, q
s (g substrate per g cells per h) revealed that the mutant grew faster than its parent. This indicated that the selected mutant
is insensitive to catabolite repression by higher concentrations of sugars for citric acid production. With respect to the
product yield coefficient ( Y
p/x), volume productivity ( Q
p) and specific product yields ( q
p), the mutant strain is significantly ( p≤0.05) improved over the parental strain. 相似文献
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