Dimyristoylphosphatidylcholine vesicle treatment enhances the storage stability and culturability of Lactococcus lactis suspensions

Maintaining bacterial culturability during storage is important for microbial biotechnology. This study evaluated dimyristoylphosphatidylcholine (DMPC) liposomes as a treatment for Lactococcus lactis suspensions stored for 28 days at 4 °C and room temperature. Liposomes were formed by thin-film hydration in the presence of bacterial cells. Cryogenic scanning electron microscopy (cryo-SEM) revealed approximately 100–160 nm vesicular structures in the DMPC-only sample and similar nanostructures near cells in treated suspensions, without establishing a continuous coating. On day 28 at 4 °C, treated and untreated suspensions had apparent zeta potentials of −17.31 and −1.56 mV, respectively. Across storage conditions and sampling times, polydispersity indices were 0.34–0.42 for treated suspensions versus 0.46–0.87 for controls, indicating lower apparent size heterogeneity. At room temperature on day 1, turbidity, expressed as optical density at 600 nm, was 0.99 versus 0.43, respectively. Metabolic activity assessed by 3-(4,5-dimethylthiazol-2-yl)− 2,5-diphenyltetrazolium bromide (MTT) reduction reached 2.50 versus 0.93 MTT-reducing units under the same conditions and subsequently declined, reaching 0.35 units in treated suspensions on day 14. Culturability was higher in treated suspensions from day 7 onward at both temperatures. On day 28 at room temperature, treated and untreated samples contained 2.55 × 10 5 and 3.83 × 10 1 CFU · mL −1 , respectively. DMPC liposome treatment thus supported retention of culturability during storage, with a larger relative benefit at room temperature, although the underlying vesicle-cell interactions remain unresolved. Key points • DMPC liposome treatment was associated with lower PDI in L. lactis suspensions. • DMPC treatment preserved L. lactis culturability during prolonged storage. • The protective effect of DMPC was strongest during room-temperature storage.