RESUMEN
The production of levan by Bacillus licheniformis NS032 in a medium based on sugar beet molasses was studied. High polysaccharide yields were produced by using diluted molasses (100-140â¯g/L of total sugars) with the addition of commercial sucrose up to 200â¯g/L of total sugars, as well as K2HPO4. A levan yield of 53.2â¯g/L was obtained on a medium optimized by response surface methodology, containing 62.6% of sugar originating from molasses, and 4.66â¯g/L of phosphate, with initial pH value of 7.2. In comparison to the media with 200 and 400â¯g/L sucrose, in the molasses optimized medium, the observed bacterial growth was faster, while the maximum production of polysaccharide was achieved over a shorter time interval (48â¯h). The polysaccharide produced in molasses medium had a weight average molecular weight of 5.82â¯×â¯106â¯Da, degree of branching 12.68%, viscosity of 0.24â¯dL/g, and based on methylation analysis and NMR data, it did not significantly differ from levan obtained in the medium with 200â¯g/L sucrose.
Asunto(s)
Bacillus licheniformis/metabolismo , Beta vulgaris/química , Medios de Cultivo/química , Fructanos/biosíntesis , Melaza/análisis , Bacillus licheniformis/efectos de los fármacos , Bacillus licheniformis/crecimiento & desarrollo , Relación Dosis-Respuesta a Droga , Fermentación/efectos de los fármacos , Fructanos/química , Cinética , Peso Molecular , Sacarosa/farmacología , ViscosidadRESUMEN
In this study, levan production by Bacillus licheniformis NS032 isolated from a petroleum sludge sample was investigated. High levan yield was obtained in a wide range of sucrose concentrations (up to 400 g/L) and, contrary to most levan-producing strains, using ammonium chloride as the sole N source. Interaction between sucrose, ammonium chloride, and initial pH of the medium in a low sucrose (60-200 g/L) and a high sucrose (300-400 g/L) system was analyzed by response surface methodology. According to the calculated model in the low sucrose system, maximum predicted levan yield was 47.8 g/L (sucrose 196.8 g/L, ammonium chloride 2.4 g/L, pH 7.0), while in the high sucrose system, levan yield was 99.2 g/L (sucrose 397.6 g/L, ammonium chloride 4.6 g/L, pH 7.4). In addition, protective effect of microbial levan against copper toxicity to Daphnia magna is observed for the first time. The acute toxicity (48 h EC50) of copper decreased from 0.14 to 0.44 mg/L by levan in concentration of 50 ppm.