Purification and characterization of poly-ε-lysine from Streptomyces noursei NRRL 5126

The present article reports on the development of an effective downstream technique for the recovery of poly-ε-lysine (ε-PL), an unusual cationic homo-polyamide of L-lysine produced by fermentation using Streptomyces noursei NRRL 5126. Purification of ε-PL using cation exchange chromatography, ultrafiltration, solvent precipitation, and gel permeation chromatography was investigated. Loading of fermentation broth on Amberlite IRC 50 chromatographic column could purify the ε-PL with 95.84% recovery. Subsequent fractionation with ultrafiltration (20kDa, and 5kDa) was found to be effective at minimal transmembrane pressure and optimal flux which resulted in 91.66% product purity. Further, solvent precipitation and gel permeation chromatography which gave the highest possible purity (97.58%) and ε-PL yield (90.42%). Exclusion of ultrafiltration step negotiated the yield (88.62%) and purity (95.15) of ε-PL, if final application doesn't demand highly pure sample. Characterization with respect to molecular weight, thin layer chromatography, IR and NMR confirmed the identity of ε-PL in purified sample.