Optimization of Medium Components and Feeding Strategies for Epsilon Poly-l-lysine Production by Streptomyces Noursei Nrrl 5126

Epsilon poly-L-lysine (ε-PL) is a nontoxic biopolymer widely used in food and pharmaceutical industry. The present work reports the nutritional requirements for submerged fermentation of Streptomyces noursei NRRL 5126 using a combination of one factor at a time and statistical orthogonal array method. Two-fold increase in ε-PL productivity (74 mg/L) was observed using optimized medium containing glycerol as carbon source along with proteose peptone and ammonium sulphate as nitrogen source. Various metabolic precursors such as amino acids, tricarboxylic acid cycle intermediates were investigated for improved production of ε-PL. Four fold increase (74 mg/L to 310 mg/L) in ε-PL production was achieved by incorporation of L-aspartate (2mM) and citric acid (5mM). Fed batch fermentation for ε-PL production with intermittent feeding with glycerol and in combination with metabolic precursors was studied. Fed batch fermentation with intermittent feeding of glycerol gave a maximum yield of 233 mg/L. Productivity was further enhanced and reached a maximum of 408 mg/L by addition of glycerol along with 5 mM citric acid after 24 h and 2 mM L-aspartate after 36 hours respectively. INTRODUCTION: Epsilon-Poly-L-lysine (ε-PL) is an unusual, naturally occurring homopolyamide of L-lysine with amide linkages between ε-amino and α-carboxyl groups 1-3 . It is biodegradable, edible and non-toxic and hence of great interest to the food and pharmaceutical industry. It was accidently discovered as an extracellular material produced by filamentous bacterium Streptomyces albulus 346 as a result of a screening for a Dragendorff positive substance. Currently ε–PL is mainly used as a natural preservative as it is harmless to human. QUICK RESPONSE CODE DOI: 10.13040/IJPSR.0975-8232.6(5).1982-91 Article can be accessed online on: www.ijpsr.com DOI link: http://dx.doi.org/10.13040/IJPSR.0975-8232.6(5).1982-91 Moreover it shows a wide spectrum of applications as an emulsifying agent, disinfectant, drug delivery carrier, endotoxin remover and biosensor and hence have attracted a great deal of attention 4 . Industrially ε-PL is produced by aerobic fermentation with Streptomyces albulus 13 . But the enzymatic and pH induced degradation of secreted ε-PL in the culture medium limits its use. Therefore there is a need to explore alternative organisms for ε-PL production 5, 6 . For a plentiful supply of ε-PL, it is necessary to develop an efficient production process. Several methods have been investigated in the hope to optimise its production for commercial usage. For example, a two phase pH control strategy 7 , immobilization of cells on baggase, synthetic sponge, macroporous silica gel, and loofah sponge 8 , etc. To achieve maximum production, knowledge regarding the