Previous studies from our laboratory have indicated that audible sound field stimulation can significantly affect E.coli growth and metabolic action, which can enhance or inhibit the growth of Escherichia coli (E.coli), and the effects of sound field on E.coli growth depended greatly on the intensity and frequency of sound field. However, very little efforts have been put forth in studying the potential mechanism of bacterial cells responses to audible sound stimulation. In this paper, the potential role of calcium signaling in mediating the response of E.coli to audible sound stimulation was firstly reported. We found that audible sound wave stimulation could evidently enhance total intracellular Ca2+ content. And the lack of calcium ion in medium significantly alleviated audible sound wave biological effects. Moreover, by adding appropriate level of calcium chloride to the LB medium contained 1.2 mM EDTA, the promotion effect of audible sound wave to E.coli growth was gradually resumed. On the basis of these findings, we speculate that calcium signaling may play an important role in mediating the response of E.coli to audible sound stimulation.
Low-energy ion implantation is a new mutation source, which has the characteristic of light damage, high mutation rate, and a broad spectrum mutation. In order to obtain industrial strain with high L-(+)-lactic acid yield, the original strain Lactobacillus casei CICC6028 was mutated by nitrogen ion beam implantation. It was found that the original strain had a higher positive mutation rate when the output power was 10keV and the dose of N+ implantation was 50×2.6×1013 ions/cm2. The mutant N-2 was obtained for many times screening and its yield of L-(+)-lactic acid was 136 g/L which was improved by 38.8% compared with the original strain whose yield of L-(+)-lactic acid was 98g/L as the cultivation time was 120h. The initial screening methods were also studied in this work but it was found that the transparent halos method was unavailable, so the initial screening was performed by shake flask fermentation. HPLC chromatogram was used to analyse the purity of L-(+)-lactic acid that was produced by the mutant strain N-2, and the result indicated the main production of N-2 was L-(+)-lactic acid and there was no other acid almost.
The paper studied on parameters of ion implantation into lipid producing strain Rhodotorula glutinis and lipid extration technology. It was found that the strain had a higher positive mutation rate when the output power was 10keV and the dose of N+ implantation was 80×2.6×1013 ions/cm2. Then a high-yield mutant strain D30 was obtained and it’s lipid yield which was 3.10 g/L increased by 33.05% than that of the original. Additionally, statistically-based experimental designs were applied for the optimization of lipid extraction by acid-heating coupling ultrasonic technique. By a Plackett-Burman design, it was found that three factors, treatment time of HCl (p=0.036) , ultrasonic time (p=0.0105) and rate of extracting solution (VCHCl3:VCH3OH) (p=0.0105), had significant effect on lipid extraction. Subsequently, these significant factors were optimized using response surface methodology (RSM), and the optimized parameters of lipid extraction were as follows: 34 min for treatment time of HCl, 7.5 min for ultrasonic treating time, 1.9:1 for rate of extracting solution (VCHCl3:VCH3OH). Finally the fermentation characteristic of high-yield mutation strain D30 was studied, when fermentation time was 10 d, it’s lipid yield increased to 7.81 g/L
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