Poly(L-diaminopropionic acid), a novel non-proteinic amino acid oligomer co-produced with poly(ε-L-lysine) by Streptomyces albulus PD-1

Poly(ε-L-lysine) (ε-PL) producer strain Streptomyces albulus PD-1 secreted a novel polymeric substance into its culture broth along with ε-PL. The polymeric substance was purified to homogeneity and identified. Matrix-assisted laser desorption ionization-time of flight mass spectrometry and nuclear magnetic resonance spectroscopy as well as other analytical techniques revealed that the substance was poly(L-diaminopropionic acid) (PDAP). PDAP is an L-aα,β-diaminopropionic acid oligomer linking between amino and carboxylic acid functional groups. The molecular weight of PDAP ranged from 500 to 1500 Da, and no co-polymers composed of L-diaminopropionic acid and L-lysine were present in the culture broth. Compared with ε-PL, PDAP exhibited stronger inhibitory activities against yeasts but weaker activities against bacteria. ε-PL and PDAP co-production was also investigated. Both ε-PL and PDAP were synthesized during the stationary phase of growth, and the final ε-PL and PDAP concentration reached 21.7 and 4.8 g L-1, respectively, in fed-batch fermentation. Citric acid feeding resulted in a maximum ε-PL concentration of 26.1 g L-1 and a decrease in the final concentration of PDAP to 3.8 g L-1. No studies on ε-PL and PDAP coproduction in Streptomyces albulus have been reported previously, and inhibition of by-products such as PDAP is potentially useful in ε-PL production.