ε -Poly-L-lysine Production from Precursor L-lysine by Streptomyces sp. M-Z18
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To investigate the process of e-poly-L-lysine(e-PL) production from precursor L-lysine under different culture conditions of Streptomyces sp.M-Z18,it has developed conversion of precursor L-lysine for e-PL production,combined with two-stage culture method,and with fermentation from glycerol,respectively.The results of experiment showed that two-stage culture method was used for conversion L-lysine to e-PL and attained at 15 g/L with biotransformation of 3 g/L L-lysine;Furthermore,e-PL production from glycerol fermentation coupled with L-lysine conversion achieved 33.76 g/L e-PL and enhanced e-PL productivity at 37.8%,compared with L-lysine-free fermentation.It was demonstrated that e-PL production could be derived from precursor L-lysine,however,the efficiency of this conversion is needed further improved.It has indicated that the limit of e-PL production is the biosynthesis of L-lysine in primary metabolism.Meanwhile,the results presented here provide a guidance for the e-PL-producing strains primary metabolism improvement by metabolic engineering,and an efficient approach to enhancement of e-PL production in scale fermentation.Keywords:
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A regulatory mutant of Brevibacterium flavum was isolated. Mutant HA42 required L-homoserine for growth and was resistant to S-(2-aminoethyl)-L-cysteine. When grown in a glucose-containing medium, mutant HA42 produced higher levels of L-lysine than the wild type. Stimulation of lysine production was observed when a low concentration of dimethyl sulfoxide was added to the glucose medium during the course of fermentation. In the best case, the lysine yield increased by 166%. The stimulatory effect of dimethyl sulfoxide on lysine production was probably due to enhanced permeability of the organism's cell wall or membrane.Key words: lysine, fermentation, surfactant, permeability, dimethyl sulfoxide.
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An enzymatic process has been proposed for producing L-lysine from DL-aminolactam by the author. Several yeasts, including Cryptococcus laurentii, have been isolated from soil and found to catalyze the selective hydrolysis of aminolactam. As well, several bacteria, including Achrornobacter obae nov. sp., have been isolated which catalyze the racemization of aminolactam. This paper reports an investigation of the conversion reaction of D- and DL-aminolactam into L-lysine using both cells of Crypt. laurentii and Achr. obae nov. sp. The optimum pH of the reaction was between 8.0 and 9.0, but most often near 8.0. An inhibitory effect of the substrates on the reaction was observed when the substrate concentration was higher than 10%, but the inhibition was slight at 5% substrate. The optimum temperature of the reaction for 3_??_6hr was around 39°C. A complete conversion reaction of 10% DL-aminolactam was carried out at 40°C for 24 hr, producing L-lysine in a conversion rate of 99.8 %. L-Lysine•HCl isolated from the reaction mixture was 99.5% optically pure.
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Epsilon-poly-L-lysine (epsilon-PL) is produced by Streptomyces albulus NBRC14147 as a secondary metabolite and can be detected only when the fermentation broth has an acidic pH during the stationary growth phase. Since strain NBRC14147 produces epsilon-PL-degrading enzymes, the original chain length of the epsilon-PL polymer product synthesized by epsilon-PL synthetase (Pls) is unclear. Here, we report on the identification of the gene encoding the epsilon-PL-degrading enzyme (PldII), which plays a central role in epsilon-PL degradation in this strain. A knockout mutant of the pldII gene was found to produce an epsilon-PL of unchanged polymer chain length, demonstrating that the length is not determined by epsilon-PL-degrading enzymes but rather by Pls itself and that the 25 to 35 L-lysine residues of epsilon-PL represent the original chain length of the polymer product synthesized by Pls in vivo. Transcriptional analysis of pls and a kinetic study of Pls further suggested that the Pls catalytic function is regulated by intracellular ATP, high levels of which are required for full enzymatic activity. Furthermore, it was found that acidic pH conditions during epsilon-PL fermentation, rather than the inhibition of the epsilon-PL-degrading enzyme, are necessary for the accumulation of intracellular ATP.
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