• Applied Biological Chemistry
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• v.41 no.1
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• pp.18-22
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• 1998

A mutant strain which hyperproduced thermostable ${\alpha}-amylase$ was obtained by chemical mutagenesis of Bacillus licheniformis. The mutant strain, SK-5, produced the enzyme about 50 times higher than the original strain. The mutant was longer and slimmer in shape, slower in growth compared to the original strain. Nucleotide sequence analysis of the SK-5 ${\alpha}-amylase$ gene revealed no changes in the the structural gene. The changes found in the promoter region might be responsible for the hyperproduction of the enzyme by the mutant. No structural changes in the enzyme structure could be observed when the secreted enzymes at various culture times were analyzed by Western blot.

• Journal of Applied Biological Chemistry
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• v.60 no.3
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• pp.249-256
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• 2017

The Monascus azaphilone (MAz) pigment is a well-known food colorant that has yellow, orange and red components. The structures of the yellow and orange MAz differ by two hydride reductions, with yellow MAz being the reduced form. Orange MAz can be non-enzymatically converted to red MAz in the presence of amine derivatives. It was previously demonstrated that mppE and mppG are involved in the biosynthesis of yellow and orange MAz, respectively. However, ${\Delta}mppE$ and ${\Delta}mppG$ knockout mutants maintained residual production of yellow and orange MAz, respectively. In this study, we deleted the region encompassing mppD, mppE and mppG in M. purpureus and compared the phenotype of the resulting mutant (${\Delta}mppDEG$) with that of an mppD knockout mutant (${\Delta}mppD$). It was previously reported that the ${\Delta}mppD$ strain retained the ability to produce MAz but at approximately 10% of the level observed in the wildtype strain. A chemical analysis demonstrated that the ${\Delta}mppDEG$ strain was still capable of producing both yellow and orange MAz, suggesting the presence of minor MAz route(s) not involving mppE or mppG. Unexpectedly, the ${\Delta}mppDEG$ strain was observed to accumulate fast-eluting pigments in a reverse phase high-performance liquid chromatography analysis. A LC-MS analysis identified these pigments as ethanolamine derivatives of red MAz, which had been previously identified in an mppE knockout mutant that produces high amounts of orange MAz. Although the underlying mechanism is largely unknown, this study has yielded an M. purpureus strain that selectively accumulates red MAz.

• Korean Journal of Agricultural Science
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• v.12 no.2
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• pp.324-332
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• 1985

Aspergillus niger B-15 with strong Endo-polygalacturonase (Endo-PG) activities was selected out from a total of 1,573 fungal strains isolated from various testing materials. A mutant strain, U-46, was obtained from the Aspergillus niger B-15 by repeated irradition of ultra-violet light. The objectives of the study were to investigate the fungal properties of the parental and mutant strains obtained and to study the condition of enzyme production and reaction. The results obtained are summarized as follows: 1. The size of conidial head of the U-46 mutant was smaller than that of the parental strains, B-15 and the length of the conidiophore was also shorter than that of the parental strains. 2. The optimum conditions for the Endo-PG production of the parental B-15 strain in the wheat bran Koji were obtained when 40% of water was added to the wheat bran and the temperature was 30 to $35^{\circ}C$. However, the best condition for the mutant U-46 strain was attained when 60 to 70% of water was added and the temperature was $35^{\circ}C$. The optimum growing periods were two to three days for both parental and mutant strains. 3. Under the optimum producing conditions of each strains, the enzymatic activity of the mutant U-46 was 20 times higher than the Endo-PG of the parental strain, B-15. 4. When both strains were cultured in the wheat bran Koji containing 60% of water at $35^{\circ}C$ for three days, the mutant strain. U-46, was about 46 times higher in the Endo-PG activity and about 18 times greater in Exo-PG activity than the parental strain, B-15. The activities of cellulase, $\alpha$-amylase, and glucoamylase were also highly increased in the mutant strain. 5. The mutant strain, U-46, increased its Endo-PG activity up to 20% over that of ordinary case when 1.2 to 1.5% of ammonium sulphate was added to the wheat bran. 6. The optimum condition for Endo-PG activity of crude enzyme of the mutant strain, U-46, was attained when pH of reaction solution was 4.0 to 4.5 and the temperature was $50^{\circ}C$.

• Microbiology and Biotechnology Letters
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• v.19 no.2
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• pp.140-146
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• 1991

Mutation experiments were performed to select the mutant of Aspergillus niger 55, which had lost almost all the ability to produce transglucosidases but retained that of high productivity of raw meal saccharifying enzyme, by means of successive induction with N-methyl-N'-nitro-N-nitrosoguanidine(MNNG), ultraviolet(UV) light, and ${\gamma}$-rays. Also, we used the mutant enrichment techniques, such as liquid culture-filtration procedure and differential heat sensitivity of conidia, in order to increase the possibility of obtaining a mutant. The glucoamylase productivity of mutant PFST-38 was 11 times higher than that of the parent strain. The mutant PFST-38 was morphologically identical to the parent strain, except for the size of conidia, the tendency to form conidia and the lenght of conidiophore. Asp. niger mutant PFST-38 apeared to be useful for the submerged production of the raw corn meal saccharifying enzyme.

• The Plant Pathology Journal
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• v.30 no.2
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• pp.215-219
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• 2014

The GacS/GacA two component system regulates various traits related to the biocontrol potential of plant-associated pseudomonads. The role of the sensor kinase, GacS, differs between strains in regulation of motility. In this study, we determined how a gacS mutation changed cell morphology and motility in Pseudomonas chlororaphis O6. The gacS mutant cells were elongated in stationary-phase compared to the wild type and the complemented gacS mutant, but cells did not differ in length in logarithmic phase. The gacS mutant had a two-fold increase in the number of flagella compared with the wild type strain; flagella number was restored to that of the wild type in the complemented gacS mutant. The more highly flagellated gacS mutant cells had greater swimming motilities than that of the wild type strain. Enhanced flagella formation in the gacS mutant correlated with increased expression of three genes, fleQ, fliQ and flhF, involved in flagellar formation. Expression of these genes in the complemented gacS mutant was similar to that of the wild type. These findings show that this root-colonizing pseudomonad adjusts flagella formation and cell morphology in stationary-phase using GacS as a major regulator.

• Journal of Microbiology and Biotechnology
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• v.12 no.2
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• pp.249-257
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• 2002

Pseudomonas fluorescens GL20 is a plant growth-promoting rhizobacterium that produces a large amount of hydroxamate siderophore under iron-limited conditions. The strain GL20 considerably inhibited the spore germination and hyphal growth of a plant pathogenic fungus, Fusarium solani, when iron was limited, significantly suppressed the root-rot disease on beans caused by F. solani, and enhanced the plant growth. The mechanism for the beneficial effect of strain GL20 on the disease suppression was due to the siderophore production, evidenced by mutant strains derived from the strain. Analysis of the outer membrane protein profile revealed that the growth of strain GL20 induced the synthesis of specific iron-regulated outer membrane proteins with molecular masses of 85- and 90 kDa as the high-affinity receptors for the ferric siderophore. In addition, a cross-feeding assay revealed the presence of multiple inducible receptors for heterologous siderophores in the strain. In order to induce increased efficacy and potential in biological control of plant disease, a siderophore-overproducing mutant, GL20-S207, was prepared by NTG mutagenesis. The mutant GL20-S207 produced nearly 2.3 times more siderophore than the parent strain. In pot trials of beans with F. solani, the mutant increased plant growth up to 1.5 times compared with that of the parent strain. These results suggest that the plant growth-promoting P. fluorescens GL20 and the genetically bred P. fluorescens GL20-S207 can play an important role in the biological control of soil-borne plant diseases in the rhizosphere.

• Journal of Microbiology and Biotechnology
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• v.30 no.4
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• pp.497-504
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• 2020

For control of brucellosis in small ruminants, attenuated B. melitensis Rev1 is used but it can be virulent for animals and human. Based on these aspects, it is essential to identify potential immunogens to avoid these problems in prevention of brucellosis. The majority of OMPs in the Omp25/31 family have been studied because these proteins are relevant in maintaining the integrity of the outer membrane but their implication in the virulence of the different species of this genus is not clearly described. Therefore, in this work we studied the role of Omp31 on virulence by determining the residual virulence and detecting lesions in spleen and testis of mice inoculated with the B. melitensis LVM31 mutant strain. In addition, we evaluated the conferred protection in mice immunized with the mutant strain against the challenge with the B. melitensis Bm133 virulent strain. Our results showed that the mutation of omp31 caused a decrease in splenic colonization without generating apparent lesions or histopathological changes apparent in both organs in comparison with the control strains and that the mutant strain conferred similar protection as the B. melitensis Rev1 vaccine strain against the challenge with B. melitensis Bm133 virulent strain. These results allow us to conclude that Omp31 plays an important role on the virulence of B. melitensis in the murine model, and due to the attenuation shown by the strain, it could be considered a vaccine candidate for the prevention of goat brucellosis.

• Journal of Microbiology and Biotechnology
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• v.26 no.11
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• pp.1908-1917
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• 2016

Wild strain L-6 was subjected to combined mutagenesis, including UV irradiation, atmospheric and room temperature plasma, and ion beam implantation, to increase the yield of 1,3-dihydroxyacetone (DHA). With application of a high-throughput screening method, mutant Gluconobacter oxydans I-2-239 with a DHA productivity of 103.5 g/l in flask-shake fermentation was finally obtained with the starting glycerol concentration of 120 g/l, which was 115.7% higher than the wild strain. The cultivation time also decreased from 54 h to 36 h. Compared with the wild strain, a dramatic increase in enzyme activity was observed for the mutant strain, although the increase in biomass was limited. DNA and amino acid sequence alignment revealed 11 nucleotide substitutions and 10 amino acid substitutions between the sldAB of strains L-6 and I-2-239. Simulation of the 3-D structure and prediction of active site residues and PQQ binding site residues suggested that these mutations were mainly related to PQQ binding, which was speculated to be favorable for the catalyzing capacity of glycerol dehydrogenase. RT-qPCR assay indicated that the transcription levels of sldA and sldB in the mutant strain were respectively 4.8-fold and 5.4-fold higher than that in the wild strain, suggesting another possible reason for the increased DHA productivity of the mutant strain.

• Microbiology and Biotechnology Letters
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• v.18 no.3
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• pp.215-220
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• 1990

Prophage cured strain derivatives from Luctobacillirs araei YIT 9018 were isolated from thermoinducible mutant of the parent lysogenic strain. Two thermoinducible mutants were isolated from L. casei YIT 9018 strain treated with N-methyl-N'-nitro-N-nitrosoguanidine. Prophage cured strains were selected after heat induction of thermoinducible strains at $42^{\circ}C$ for 30 min in MRT medium containing anti- 4 FSV serum. The prophage cured strains, L. casei HYM 1213 and L. casei HYM 4024, could be used an indicator strain for temperate phage $\phi$ FSW. The growth, lactic acid producing ability and carbohydrates fermentation of L. casei HYM 1213 were similar to the parent L. cmei YIT 9018 strain, but A. casei HYM 4024 was not. One of the prophage cured strain, L. cmei HYM 1213, could be used industrially .to produce lactic acid beverages because this strah could not induce the virulent phage$\phi$FSV. The physiological characterization of L. casei HYM 1213 strain was similar to the parent L. casei YIT 9018 strain.

• Journal of the Korean Society of Tobacco Science
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• v.12 no.1
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• pp.9-18
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• 1990

To study the determinants which are involved in the loss of pathogenicity in wilt-inducing Pseudomoms solamcewum, several physlologica I functions were compared in a virulent P. solanacearum strain and an avirulent, spontaneously derived mutant strain. The polyacrylamide gel electrophoresis showed the distinction between two strains in the patterns and the relative intensity of proteins produced intracellularly or extracellularly. Enzyme assays showed that the level of polygalacturonase activity in the culture filtrate of the avirulent mutant was markedly reduced, while carboxymethylcellulase(rondoglucanase) activity in both strains were nearly negligible. These results suggest that the loss of pathogenicity in mutant strain is attributed in part to the reduced production of polygalacturonase. In audit ion, comparative analyses by agarose gel electrophoresis of DNA molecules isolated from both strains show that the pathogenicity genes of p. solanaceerum are not located on plasmid but are on chromosome.