High Cell-density Fermentation Of Streptomyces Albulus For ε-Poly-L-Lysine Production

ε-poly-L-lysine (ε-PL) produced by Streptomyces strains, is a homopolymer of L-lysinewith a pomerization degree of25~30residues. Due to its highly safety and biodegradation,ε-PL is being received increasing interest as a natural food bio-preservative. The fermentationof ε-PL has been industrialized in Japan. But the fermentation technology of ε-PL is notmature in our country. So the study on production technology of ε-PL proved to have greatvalues.In the essay, Streptomyces albulus mutant was studied which was inoculated intoresistant petri dish filled with Gly and ε-PL medium in order to screen a highε-poly-L-lysine-producing strain after treated by UV and diethyl sulphate (DES). First, theshake flask fermentation conditions of Streptomyces albus was optimized, such as liquidvolume, inoculation amount and the initial medium sugar concentration in250mL shakeflasks. The results showed that the best conditions were50mL liquid volume,6%(v/v)inoculation amount,5%initial medium sugar concentration, respectively. And under thisfermentation condition, the dry cell weight and the yield of ε-PL were up to4.48g/L and0.49g/L.Then, the influence of adding of sodium citrate and biotin was also researched and theresults showed that the influence of sodium citrate concentrations was not obvious on cellgrowth, but noticeable on synthesis of ε-PL. Adding2g/L sodium citrate at0h got thehighest ε–PL concentration0.92g/L. The reason may be due to the rising of pH value withthe addition of sodium citrate. By adding2g/L sodium citrate at0h and300μg/L biotin at36h in fermentation, the highest cell dry weight and ε–PL yield were reached to7.86g/L and1.10g/L respectively, which were1.30and1.93folds to the control respectively. Itdemonstrated that adding sodium citrate and biotin could promote cell growth and ε-PL yieldby fermentation of S. albulus.The high cell density culture (HCDC) of ε-poly-L-lysine-producing Streptomycesalbulus DES-2via repeated batch perfusion was studied. To investigate the effect of therepeated batch perfusion culture on cell growth and ε-PL yield, the starting time of first batchperfusion was set at the prophase of the logarithmic (24h), the early stationary (48h), and thelate stationary phases (60h), respectively, followed by batch perfusion every24h; throughfurther researched on the effect of continuing to culture after starting once batch perfusion indifferent times and the60h-startup group with just three batch perfusion on cell growth andε-PL yield, the results showed that the batch perfusion times should be limited in3and the starting time of first batch perfusion should be in the prophase of the late stationary phase.12.79g/L of the dry cell weight and1.11g/L of ε-PL yield were achieved at24hours in the3rd batch perfusion culture, which were3.07and2.27folds to maximum value of the controlat60hours respectively. Further cultivated to48h, cell dry weight would decrease whichindicated that most cells got into decline phase, but ε-PL quantity synthesized to themaximum value of1.71g/L,3.5times more than the conventional culture, mean that a largenumber of ε-PL accumulated in the stationary phase and decline phase. The study suggestedthat high cell density culture and ε-PL production of S. albulus DES-2could be nicelyachieved by batch perfusion culture.