Omega-3 fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have beneficial effects on human health. The probiotic bacterium Escherichia coli Nissle is unable to produce either EPA or DHA. Escherichia coli Nissle was transformed with the pfBS-PS plasmid carrying the EPA/DHA gene cluster, previously isolated from a marine bacterium. The transgenic E. coli Nissle produced EPA when grown at 10ºC (16.52 ± 1.4 mg g(-1) cell dry weight), 15ºC (31.36 ± 0.25 mg g(-1) cell dry weight), 20ºC (13.71 ± 2.8 mg g(-1) cell dry weight), 25ºC (11.33 ± 0.44 mg g(-1) cell dry weight) or 30ºC (0.668 ± 0.073 mg g(-1) cell dry weight). Although DHA was also produced at all these temperatures, it comprised less than 0.2% of total extracted fatty acids. Transcriptomic analysis using Reverse Transcription qPCR showed upregulation of the entire gene cluster in E. coli Nissle. Among EPA/DHA genes, pfaB, pfaC and pfaD were overexpressed (expression ratio of 181.9, 39.86 and 131.61, respectively) as compared to pfaA (expression ratio of 3.40) and pfaE (expression ratio of 4.05). The EPA/DHA-producing probiotic E. coli Nissle may be used as a safe, alternative and economic source for the industrial and pharmaceutical production of EPA and DHA.
In this paper, the effect of different pulse and system parameters on the killing efficiency of PEF treatment was investigated. Escherichia Coli bacteria inoculated in apple juice was treated. The results showed that an electric field higher than 4 kV/mm is required to enhance the killing efficiency using PEF that has sufficient log reductions in the microbial numbers. The temperature rise during pulse application was found to be around 20 o C, and it is observed that this rise in medium temperature has synergistic effect and has resulted in high inactivation. As the temperature rise can be limited to a value below the pasteurization temperature, the synergistic effect can be highly beneficial. While high killing rate was achieved for inoculated bacteria (3-4 log reduction), less than 2 log reduction was achieved for naturally growing bacteria in apple juice under the test conditions used.
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