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The activity of amylases obtained under chemostat conditions was found between 92 to 118 U/mL, but this highly effective biosynthesis was a short-lived process. Continuous amylase synthesis in a packed-bed reactor (carried out for 144 h) by the bacteria immobilized in calcium alginate resulted in slow reduction of cell productivity of amylases ranging from 69.5 to 44.7 U/g of biocatalyst. Amylase biosynthesis in this process was to a large extent dependent on the dilution rate (D). The highest effectiveness of bacteria production (Yp/x= 36.1 U/g beads) was obtained at D=0.8 h-1, while the highest volumetric productivity Qp= 98 kU/Lh was observed at D=6.4 h-1. The bacteria cells immobilized in chitosane gel beads exhibited high yield (70-73 U/g beads) for 96 h of incubation, which was followed by a rapid decrease.
The purpose of the study was to evaluate the effectiveness of preservation of two bacteria strains: Bacillus subtilis B-3 and Bacillus poly my xa В-20 (proteinase and amylase producers) in the form of dried spores on glass beads. In our study we have found that the survival level of the two strains after 15 months of storage was 100%. The viability of B. subtilis B-3 was 20% lower than that of the control culture maintained by subculturing on agar slants and stored at 4°C (µ = 1.8 h-1 and µ = 2.16 h-1), whereas the viability of B. polymyxa B-20 was similar to that of the control culture (µ = 1.3 h-1). The biosynthetic capability of B. polymyxa B-20 remained at unchanged levels of 303 FSU and 2.5 AU, but only when the spores had been stored on glass beads with starch as the protective agent. The biosynthetic activity of B. subtilis B-3 was 76% lower in the case of proteinases and 60% lower in the case of amylases. The method of storage of bacteria in the form of spores dried on glass beads, described in this paper, can be recommended for B. polymyxa B-20 strain, but it is not suitable for B. subtilis B-3 since the bacteria have lost, to a large extent, their biosynthetic ability.
The aim of the study was to determine optimal conditions for amylases biosynthesis by immobilized Bacillus polymyxa В-20 cells. Composition of the medium and immobilization conditions to a large extent affected the efficiency of enzyme production. Optimal production medium consisted of yeast extract (5-10 g/L), maltose, peptone and mineral salts. Stability of alginate biocatalyst beads was increased by 30 g/L gel concentration, increased bead size and chemical gel modification by glutaraldehyde. Increased quantities of synthesized enzymes were proportional to the increment of initial biomass present in beads, and to a lesser degree, depended on quantities of immobilized inoculum. In repeated batch culture, the bacteria immobilized in alginate were able to synthetize 32% more enzymes than those immobilized in chitosane. Operational stability of alginate and chitosane beads was maintained for 17 days.
Keratinolytic abilities of Bacillus polymyxa B20 and B. cereus B5esz were evaluated in liquid cultures in mineral media containing chicken feathers. Both tested strains were capable of effective liquefying and biodegradation of feather keratin, up to 56.5 – 72.1% in ten-day cultures, releasing considerable amounts of hydrolysis products. Tested bacteria were mesophilic species, producing highest activity of keratinases and proteases in the presence of keratin (1%) as a sole nutrient source or keratin supplemented with yeast extract, at 30℃. Keratinases of B. polymyxa were predominantly highly alkaline serine proteases, with optimum activity at 50℃, while B. cereus produced mainly a mixture of neutral proteases, optimally active at 45℃. Keratinolytic potential of tested bacterial strains could find a variety of applications, including utilization of keratinous waste from poultry industry and obtaining keratin hydrolysate-based soil fertilizers.
Antagonistic effect of Bacillus polymyxa, strain S13, toward Fusarium oxysporum f. sp. tulipae was evaluated in vitro and in vivo. The growth of the pathogen was greatly inhibited in dual cultures with Bacillus polymyxa on potato dextrose agar. Suspension of B. polymyxa and its filtrate substantially inhibited spore germination and development of Fusarium oxysporum f. sp. tulipae on tulip bulbs.
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