Effects of cultivation conditions on D-aspartate production by the lactic acid bacterium Latilactobacillus curvatus strain WDN19.

D-Asp is a pharmaceutically valuable amino acid used as an antibiotic precursor and has potential therapeutic benefits for neurological disorders and reproductive health. The lactic acid bacterium Latilactobacillus curvatus strain WDN19, originally isolated from a salt-fermented pickle, produces large amounts of D-Asp from L-Asp. To optimize D-Asp production, we investigated the effects of various cultivation conditions. Growth and D-Asp formation increased concomitantly with temperature, reaching a maximum at 37 °C, whereas no growth occurred at 40 °C. L-Asp concentrations ≤ 100 mM minimally affected biomass, yet higher levels curtailed both growth and conversion, revealing an intrinsic racemization capacity of ~ 30 mM under unbuffered conditions. Strain WDN19 grew across an initial pH range of 5.0-9.5, but rapid acidification to pH ≈ 4.5 triggered severe cell death and arrested D-Asp synthesis. Incorporation of 500 mM 2-morpholinoethanesulfonic acid maintained near-neutral pH, preserved viability, and enabled almost quantitative racemization of up to 500 mM L-Asp within 48 h, yielding > 250 mM D-Asp. These findings establish pH control as the critical determinant for high-yield D-Asp production by strain WDN19, providing a practical framework for environmentally friendly, fermentation-based manufacturing of this pharmaceutically valuable amino acid.