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Liu Shengrong,Wu Qingping,Zhang Jumei,Mo Shuping 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.6
ε-Poly-L-lysine (ε-PL), produced by Streptomyces or Kitasatospora strains, is a homo-poly-amino acid of Llysine,which is used as a safe food preservative. In this study, the effects of L-lysine and its isomer, D-lysine, on ε-PL biosynthesis and their metabolites by the ε-PLproducing strain Streptomyces ahygroscopicus GIM8 were determined. The results indicated that L-lysine added into the fermentation medium in the production phase mainly served as a precursor for ε-PL biosynthesis during the flask culture phase, leading to greater ε-PL production. At an optimum level of 3 mM L-lysine, a ε-PL yield of 1.16 g/L was attained, with a 41.4% increment relative to the control of 0.78 g/L. Regarding D-lysine, the production of ε-PL increased by increasing its concentrations up to 6 mM in the initial fermentation medium. Interestingly, ε-PL production (1.20 g/L) with the addition of 3 mM D-lysine into the initial fermentation medium in flasks was higher than that of the initial addition of 3 mM L-lysine (1.06 g/L). The mechanism by which D-lysine improves ε-PL biosynthesis involves its utilization that leads to greater biomass. After S. ahygroscopicus GIM8 was cultivated in the defined medium with L-lysine, several key metabolites, including 5-aminovalerate, pipecolate, and L-2-aminoadipate formed in the cells, whereas only L-2-aminoadipate was observed after D-lysine metabolism. This result indicates that Llysine and D-lysine undergo different metabolic pathways in the cells. Undoubtedly, the results of this study are expected to aid the understanding of ε-PL biosynthesis and serve as reference for the formulation of an alternative approach to improve ε-PL productivity using L-lysine as an additional substrate in the fermentation medium.
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Yang, Xiaojuan,Wu, Qingping,Zhang, Jumei,Guo, Weipeng,Mo, Shuping,Liu, Shengrong 한국식품과학회 2016 Food Science and Biotechnology Vol.25 No.4
This study aimed to classify a collection of Enterobacter sakazakii (E. sakazakii) strains previously identified from powdered infant formula (PIF) to species level by recN gene sequencing and biochemical testing to determine the distribution of Cronobacter species in China and investigate the strain diversity by cellular fatty acid (CFA) analysis. Of 24 E. sakazakii isolates, 23 were identified as C. sakazakii and one was C. malonaticus. The 23 C. sakazakii isolates showed the same CFA profiles. The C. malonaticus isolate was discriminated from the C. sakazakii isolates by the significant difference in the amounts of $C_{12:0}$, $C_{14:0}$, and $C_{17:0\;cyclo}$ acids. These results showed that C. sakazakii and C. malonaticus were the common Cronobacter species distributed in PIF in China and that the isolates of the two species exhibited different CFA profiles. These findings are of value for epidemiological investigations and provide an alternative method for confirming various Cronobacter spp.
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