Among 27 filamentous fungi, a strain Aspergillus niger An76 gave the highest siderophore yield even when cultured on natural medium or minimal medium containing 1 mmol L^-1 Fe^3＋. Whereas for most other strains, the ...Among 27 filamentous fungi, a strain Aspergillus niger An76 gave the highest siderophore yield even when cultured on natural medium or minimal medium containing 1 mmol L^-1 Fe^3＋. Whereas for most other strains, the capacities of siderophore production was repressed as the concentrations of Fe^3＋ was higher than 20 ~tmol L^-1. Lower ferric iron concentrations were more conducive to siderophore synthesis for those strains. The An76 siderophore was partially purified through a series of chromatography steps using Sephadex LH20 and CM-Sepharose Fast Flow columns. Its structural characteristics differed from typical siderophores, such as catecholates or hydroxamates, and no amino acids or peptide bonds were detected. It may therefore represent a new type of siderophore structure. TBA assay and ESR trapping studies showed that An76 siderophore had remarkable scavenging activity of hydroxyl free radicals in vitro. The antibiotic activities of siderophores produced by An76 were tested against 29 bacterial strains, including plant, animal, and human pathogens. The growth of 14 bacterial strains could be completely inhibited at a siderophore concentration of 8 mg ml^-1 with an incubation time of 30 min. Evidence suggests that the An76 siderophore has potential value as an antioxidant and a biocontrol agent against pathogenic microorganisms.展开更多
Aspergillus oryzae 3042 mycelium pellets were immobilized by crosslinking method with reagents of gelatin and formaldehyde. An orthogonal design table was used to determine the optimal immobilization conditions. The L...Aspergillus oryzae 3042 mycelium pellets were immobilized by crosslinking method with reagents of gelatin and formaldehyde. An orthogonal design table was used to determine the optimal immobilization conditions. The L-aminoacylase activity of immobilized mycelium pellets under optimal conditions was assayed. The results show that the L-aminoacylase activity was 1350 U·g^-1 and the activity retention rate was 83%. The properties of the immobilized preparation were studied. Compared with free pellets, the appropriate pH of reaction system changed from 7.0 to 8.0, temperature changed from 52℃ to 63℃, and the ranges of the optimum reaction conditions were all improved. The effect of Co^2＋ on immobilized mycelium pellets was investigated and the favorable concentration was determined. When the immobilized preparation was used for the resolution of D, L-alanine in a packed bed reactor with 10 mm in diameter, 200 mm in height, the operational stability was increased, and the half-life period was 53 d. Thermal stability analysis shows that the immobilized pellets were more stable than the free pellets.展开更多
基金This work was supported by the National Natural Science Foundation of China （No. 30470051）, the Major State Basic Research Development Program of China （973, No. 2004CB7197）, and the Natural Science Foundation of Shandong Province （No. Y2004D07）.
文摘Among 27 filamentous fungi, a strain Aspergillus niger An76 gave the highest siderophore yield even when cultured on natural medium or minimal medium containing 1 mmol L^-1 Fe^3＋. Whereas for most other strains, the capacities of siderophore production was repressed as the concentrations of Fe^3＋ was higher than 20 ~tmol L^-1. Lower ferric iron concentrations were more conducive to siderophore synthesis for those strains. The An76 siderophore was partially purified through a series of chromatography steps using Sephadex LH20 and CM-Sepharose Fast Flow columns. Its structural characteristics differed from typical siderophores, such as catecholates or hydroxamates, and no amino acids or peptide bonds were detected. It may therefore represent a new type of siderophore structure. TBA assay and ESR trapping studies showed that An76 siderophore had remarkable scavenging activity of hydroxyl free radicals in vitro. The antibiotic activities of siderophores produced by An76 were tested against 29 bacterial strains, including plant, animal, and human pathogens. The growth of 14 bacterial strains could be completely inhibited at a siderophore concentration of 8 mg ml^-1 with an incubation time of 30 min. Evidence suggests that the An76 siderophore has potential value as an antioxidant and a biocontrol agent against pathogenic microorganisms.
文摘Aspergillus oryzae 3042 mycelium pellets were immobilized by crosslinking method with reagents of gelatin and formaldehyde. An orthogonal design table was used to determine the optimal immobilization conditions. The L-aminoacylase activity of immobilized mycelium pellets under optimal conditions was assayed. The results show that the L-aminoacylase activity was 1350 U·g^-1 and the activity retention rate was 83%. The properties of the immobilized preparation were studied. Compared with free pellets, the appropriate pH of reaction system changed from 7.0 to 8.0, temperature changed from 52℃ to 63℃, and the ranges of the optimum reaction conditions were all improved. The effect of Co^2＋ on immobilized mycelium pellets was investigated and the favorable concentration was determined. When the immobilized preparation was used for the resolution of D, L-alanine in a packed bed reactor with 10 mm in diameter, 200 mm in height, the operational stability was increased, and the half-life period was 53 d. Thermal stability analysis shows that the immobilized pellets were more stable than the free pellets.
