Mutants Of Aspergillus Niger Research Articles

Increased citric acid production by mutants ofAspergillus nigerwith increased glycolytic capacity

Mutants of Aspergillus niger were selected according to their ability to grow faster than the parent strain on solid media containing 14% (w/v) sucrose. Among 9 mutants, 4 exhibited significantly increased (> 20% of control) citric acid production. These mutants exhibited strongly increased activities of two glycolytic enzymes, hexokinase and phosphofructokinase. The mutants took up low concentrations (1%, w/v) sucrose at a comparable rate to the parent strain but exhibited a faster uptake of high (14%, w/v) sucrose concentrations.

Aspergillus niger mutants with increased glucose oxidase production

Aspergillus niger NRRL-3, an organism used for the industrial scale production of d-gluconic acid and glucose oxidase (EC 1.1.3.4), was subjected to mutagenesis and selection for acid production on diagnostic media containing methyl red. The plates contained 0.1 M d-glucose, a concentration that does not produce a color change in the medium surrounding mycelia of the parental strain under the conditions employed. Mutagenized spores yielded occasional colonies which were able to grow rapidly and were surrounded by a reddish zone. A number of such presumptive mutants were selected and isolated. Twenty-six such strains were grown in shaken cultures with liquid media containing 0.01, 0.1 or 0.5 M d-glucose, harvested, disrupted and the specific activity of d-glucose oxidase determined. Seven of the mutant strains had glucose oxidase specific activities markedly higher than the parental strain.

Lipid composition and amino acid transport in a nystatin-resistant mutant of Aspergillus niger.

A nystatin-resistant mutant of Aspergillus niger has been isolated and used as a model system to study the effect of altered sterol levels on lipid composition, transport behavior and physical properties of membrane lipids. There is a decrease in the sterol to phospholipid ratio in the mutant compared to the wild type. Although there is no qualitative change in phospholipid composition, the mutant contains a higher amount of phosphatidylcholine and a lower amount of phosphatidylethanolamine compared to the wild type. The most significant change is the elevated level of linoleic acid in the mutant, concomitant with a decreased level of oleic acid. These adaptive changes to nystatin resistance are manifested in the altered thermotropic behavior of membrane lipids as studied by the steady-state fluorescence polarization technique. These changes are also associated with altered membrane permeability as evidenced by the change in Vmax values for uptake of some amino acids in the mutant compared to the wild type.

Selection of amylolytically active Aspergillus niger mutants to 2-deoxy-D-glucose

As a result of mutagenization and passaging on 2-deoxy-D-glucose containing medium, 10 Aspergillus niger strains resistant to this agent were obtained. These showed (with one exception) an increase in the activity of glucoamylse, the level of which ranged widely in individual cases from several to over 200% in comparison with the parent strain. A weaker rate of glucose accumulation in derepressed strains may account for the fact that the mechanism of their resistance to deoxyglucose is connected with disturbance of the system of glucose transport. However, it is possible that a high activity of acid phosphatase, which the obtained deoxyglucose-resistant cultures showed, may be involved here. Apart from the biochemical character of the catabolic derepression, it seems that it can already be successfully utilized to increase the productivity of industrial mould cultures.

Semi-pilot scale production of citric acid in cane molasses by gamma-ray induced mutants of Aspergillus niger

Utilizing cane molasses as substrate, semi-pilot scale production of citric acid was investigated in fermentation trays (40 × 35 cm) with several gamma-ray induced mutants of Aspergillus niger. Of the mutants tested, two were found to have high yield efficiency ( 14 20 , 51.06%; 79 20 , 50.35% ) of sugar to citric acid. The yield of other mutants (HB3, 10 20 , 164 20 , 277 30 and 112 40 ) ranged between 30 to 42%. The prospect of utilizing the high yielding mutants for commercial production of citric acid have been discussed.

Inhibition of citric acid accumulation by manganese ions in Aspergillus niger mutants with reduced citrate control of phosphofructokinase.

Mutant strains of Aspergillus niger with reduced citrate control of carbohydrate catabolism (cic mutants) grow faster than the parent strain on media containing 5% (wt/vol) citrate. The mutants tolerated a higher intracellular citrate concentration than the parent strain. One mutant (cic-7/3) contained phosphofructokinase activity significantly less sensitive towards citrate than the enzyme from the parent strain. When this mutant was grown under citrate-accumulating conditions, acidogenesis was far less sensitive to inhibition by Mn2+ than in the parent strain. Some of the cic mutants also showed altered citrate inhibition of NADP-specific isocitrate dehydrogenase.

Semi-pilot scale studies on citric acid fermentation by a gamma-ray induced mutant of Aspergillus niger

Semi-pilot scale production of citric acid was investigated with a gamma-ray induced mutant (HB3) of Aspergillus niger using 500, 1000 and 1500 ml medium in 51 fermentation jars. Yield of citric acid was found to be seven-fold higher compared to the parent in 1000 ml medium and the corresponding increase was two-fold in the 500 ml medium. With 1500 ml/fermentation jar the yield was low with both the parent and the mutant strain though the mutant gave higher yield compared to the parent.

Induction, isolation, and characterization of aspergillus niger mutant strains producing elevated levels of beta-galactosidase

An Aspergillus niger mutant strain, VTT-D-80144, with an improvement of three- to fourfold in the production of extracellular beta-galactosidase was isolated after mutagenesis. The production of beta-galactosidase by this mutant was unaffected by fermentor size, and the enzyme was also suitable for immobilization.

A new type of interaction between spore colour mutants ofAspergillus niger

A new white-spored mutant of the imperfect fungusA. niger is described. Behind the heterokaryotic heads formed with non-allelic spore colour mutants, it shows as a result of crossfeeding a uniform change of colour of the conidial heads in a band up to 4–5 mm deep. This mutation with pleiotropic effects on colour and crossfeeding occurs relatively frequently inA. niger, although it has not been reported previously.

Accumulation of 2-oxo acids in mutants of Aspergillus niger requiring lysine.

Mutants of Aspergillus niger 194A and 178 requiring lysine differ from the original prototrophic strain K10 and from each other on the course of accumulation of organic acids. In both mutants less citric acid accumulates during the first phase of cultivation but considerably more 2-oxoglutarate and 2-oxoadipate accumulate than in the original strain. Whereas in the 194A mutant this state remains unchanged also during the second phase of cultivation, in the 178 mutant oxo acids are degraded and citric acid is synthesized intensively. The accumulation of 2-oxoglutarate and 2-oxoadipate in the fermentation medium indicates that in A. niger lysine is synthesized via the homocitrate pathway.

Parasexual hybridisation and citric acid production by Aspergillus niger

In this investigation hybridisation experiments were performed with two auxotrophic mutants of Aspergillus niger. A heterozygous diploid was derived from them and it produced segregants including parental haploids and a recombinant. Their yield characters were studied.

Effect of respiratory deficiency and temperature on the mitochondrial lipid metabolism of Aspergillus niger

A comparative study of the mitochondrial lipid composition of a wild strain (V 35) and a respiratory-deficient mutant (rd3) of Aspergillus niger grown at different temperatures (25, 30, 35, and 40 degrees C) has been performed. The lipid spectrum, though qualitatively similar, differs quantitatively in both cases. At the optimum growth temperature (30 degrees C) depletion in ergosterol (40%) and cardiolipin (52%) was observed. This probably indicates the formation of defective mitochondria in the mutant with a resultant impaired respiratory system. Complete depletion of cardiolipin species containing fatty acid (20:5omega3) in the respiratory-deficient mutant suggests a possible role of this lipid in mitochondriogenesis at least in A. niger. The effect of temperature is predominantly on the degree of unsaturation and sterol ester formation. The linoleic acid (18:2omega6) content decreases with a concomitant increase in oleic acid (18:1omega9) content as the growth temperature increases for both cell types. Some morphological changes and effects on the vegetative life cycle have been observed with variation in growth temperature in the wild type and also in the mutant form.

Catabolite repression of hydrolases in Aspergillus niger

A comparative study was made on catabolite repression of acid protease and polygalacturonase in an adenine-requiring mutant of Aspergillus niger. Both enzymes are inducible and accumulated extracellularly after cessation of growth caused by adenine starvation. Addition of glucose, fructose, or intermediates of glycolysis, but not tricarboxylic acid cycle intermediates, depressed the formation of both enzymes. Catabolite repression of polygalacturonase by glucose occurred quickly and was almost complete. However, acid protease was only partly repressed even after several hours. Formation of polygalacturonase in the presence of actinomycin S3 or during deinduction was repressed by glucose, whereas that of acid protease was not. In the course of induction of acid protease by peptone, glucose did not affect the length of the induction lag period and the rate of acid protease formation decreased by glucose was not restored by the addition of large amounts of inducer. From these results, we suggest that catabolite repression of polygalacturonase occurs at the level of translation and that of acid protease at transcription.

A turbidimetric method for the screening of amylase-producing mutants of Aspergillus niger.

The method is based on the assumption that extracellular amylase, which is produced by strains of Aspergillus niger in liquid culture, hydrolyses the starch in the media and brings about a corresponding decrease in the turbidity of the media. Mutant strains which produced different quantities of amylase exhibited different degrees of decrease in turbidity of the media. The results showed that a greater degree of decrease in turbidity was observed for a higher quantity of amylase produced.

Isolation and analysis of conidiation defective mutants of Aspergillus niger

Mutants defective in sporulation were isolated following gamma-irradiation of a wild type strain of Aspergillus niger. A complementation study was undertaken by growing 12 such mutants in pairwise combinations, and it was shown that they belonged to six different complementation groups. Parental types were recovered from the spores resulting from a complementing pair of mutants indicating that heterokaryotic heads were formed. “Aconidial” parents could be recovered from heterokaryotic conidial heads occurring due to pairing of “aconidial” and “coloured” conidial mutants.

Evaluate the effect of mutans Aspergillus niger to the nutritive value of fermentation at coconut meal and karnel palm meal

Agricultural wastes, such as coconut meal and kernel palm meal can be used to fulfill the need of feed for ruminants ormonogastrics. Fermentation technology using Aspergillus niger has been reported allow to increase their nutritive value.Isolation of the asporogenous strain which could spored at room temperature but could not spored at 37oC is expected to sole the fermentation of spores in the fermentation product. The spore formation of mutants at the fourth day incubationtime (10%) was less than the wild type (100%). The variance analysis of protein content in vitro Dry Matter Digestibility (IVDMD) and in vitro Protein Digestibility (IVPD) showed that the kind of mutants were interacted with the incubation time(P<0,01). The highest protein content of coconut meal was obtained from E27 mutant (33.0%), kernel palm meal wasobtained from E14 mutant (31.4%) at the fourth day of incubation time. The highest IVDMD of coconut meal (62.1%), kernel palms meal (61.8%) at the fourth day incubation time and from all E27 mutant. The highest IVPD of coconut meal was obtained from E27 mutant (20.49%) at the fourth day incubation time, kernel palm meal was obtained from E27 mutant (18.66%) at the fourth days incubation time.© 2004 Jurusan Biologi FMIPA UNS SurakartaKeywords: mutant Aspergillus niger, coconut meal, kernel palm meal, fermentation

Genetic analysis of the coloured mutants of Aspergillus niger.

Seven different classes of coloured mutants were produced in anAspergillus niger strain: brown (B), cinnamon (C), dark brown (DB), fawn (F), green (G), yellow (Y) and white (W). A few of these recurrent colour mutants were allelic and the rest was non-allelic. These were tested by complementation test in heterocaryons. A few colour mutants failed to form heterocaryons. The incompatibility is suggested to be under genetic control. Conidial size of the heterocaryotic heads was measured and found to be significantly larger than that of their parental homocaryons. It is believed that the larger size is due to heterocaryotic vigor manifested in the conidia from heterocaryotic mycelium. It is termed haploid inherited vigor.

Isolation of auxotrophic mutants ofAspergillus niger by ethylmethane sulphonate treatment

The alkylating agent EMS can be employed for the isolation of auxotrophic mutants of theAspergillus niger strain K 10. The maximum number of auxotrophic mutants (2.9–5.1%) corresponded approximately to the number of mutants obtained by EMS treatment of yeasts, but it was by order lower than the number of mutants generally obtained by EMS treatment in bacteria. The majority of isolated mutants grew worse than the parent strain in the liquid medium and also formed lower amount of organic acids. The organic acid which was most frequently accumulated by mutants was citric acid.

Transformation of nutritionally deficient mutants of Aspergillus niger.

SUMMARY: Reversions to wild type occurred when conidia of a number of biochemically deficient mutants of Aspergillus niger were treated with DNA from the wild-type strain. No reversions or wild-type colonies were obtained when an equivalent number of conidia from deficient strains were either treated with the same DNA as the recipient, or were plated without any DNA treatment. Increase in the percentage of transformation was observed up to 6 μg./ml. of donor DNA. The transforming activity of the donor DNA was found to be inhibited by the action of u.v. radiation, heat and DNase. The frequency of transformation was low which could be attributed to the method of extraction of DNA which involved crushing of cells in the presence of alumina, possibly breaking the DNA into small fragments thus making it biologically less active.

The Effect of Lipids on Citric Acid Production by an Aspergillus niger Mutant

SUMMARY: A mutant strain, 72--44, of Aspergillus niger was selected after ultraviolet irradiation of the spores of A. niger strain 72--4. This mutant was capable of giving high yields of citric acid in shaken flask fermentations. A study was made of the effect of various lipids on the yield of citric acid produced by A. niger strain 72--44. Fatty acids with less than 15 carbon atoms inhibited growth and no citric acid was produced. Natural oils with a high content of unsaturated fatty acids and oleic acid itself, when added at 2% (v/v) to suitable fermentation media, increased the yield of citric acid by about 20%. Lipids which improved the yield of citric acid had no effect on the dry weight of mycelium. The possible mode of action of effective lipids is discussed. It is suggested that unsaturated lipids act as alternative hydrogen acceptors to oxygen during the fermentation and thus improve the yield of citric acid.