Abstract
Epsilon poly-l-lysine (ε-PL) is a homo-biopolymer with approximately 25–30 l-lysine residues. It is a promising natural biopolymer widely used in food and pharmaceutical industry. The present work reports enhanced production of ε-PL with a novel producer Bacillus cereus using amino acids and TCA cycle intermediates in the fermentation medium. Among the various amino acids and TCA cycle intermediates tested 2 mM l-aspartic acid and 5 mM citric acid gave ε-PL yield of 145.5 and 230 mg/L, respectively. A combination of citric acid after 24 h and l-aspartic acid after 36 h improved ε-PL yield from 85 mg/L (control) to 335 mg/L. Glucose feeding strategy along with metabolic precursors was employed which further enhanced ε-PL yield to 565 mg/L. Thus, more than sixfold increase in ε-PL yield was achieved suggesting the potential of Bacillus cereus as a novel ε-PL producer.
Highlights
Introduction ePoly-L-lysine (e-PL) is a basic homo-poly-amino acid characterized by a peptide bond between e-amino and a-carboxyl groups of L-lysine
The present work reports enhanced production of Epsilon poly-L-lysine (e-PL) with a novel producer Bacillus cereus using amino acids and Tricarboxylic acid (TCA) cycle intermediates in the fermentation medium
Tricarboxylic acid (TCA) cycle is a critical catabolic pathway which provides important precursors for the biosynthesis of amino acids, nucleic acids, lipids and polysaccharides. e-PL is a linear polymer synthesized from L-lysine monomers by the formation of amide bonds between e-amino and a-carboxyl groups
Summary
Poly-L-lysine (e-PL) is a basic homo-poly-amino acid characterized by a peptide bond between e-amino and a-carboxyl groups of L-lysine. It is a secondary metabolite, mainly produced by bacteria belonging to the family of Streptomycetaceae (Shima and Sakai 1977, 1981a, b). E-PL is a linear polymer synthesized from L-lysine monomers by the formation of amide bonds between e-amino and a-carboxyl groups. Diaminopimelic acid is formed via aspartate produced by transamination of oxaloacetate. Studies suggest that addition of citric acid to the production medium facilitates the conversion of oxaloacetate to aspartate by inhibiting the cycle forming reaction to citrate (Bankar and Singhal 2011).
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