Abstract
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 400g/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 (60-200g/L) and a high sucrose (300-400g/L) system was analyzed by response surface methodology. According to the calculated model in the low sucrose system, maximum predicted levan yield was 47.8g/L (sucrose 196.8g/L, ammonium chloride 2.4g/L, pH 7.0), while in the high sucrose system, levan yield was 99.2g/L (sucrose 397.6g/L, ammonium chloride 4.6g/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 (48h EC50) of copper decreased from 0.14 to 0.44mg/L by levan in concentration of 50ppm.
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