Sodium hydroxide-induced Weissella kimchii ghosts (WKGs) as immunostimulant

Abstract

Background Bacterial ghosts (BGs) are bacterial envelopes without any internal content. BGs have been investigated as a new vaccine delivery platform and an adjuvant. Commonly, BGs are generated from gram-negative bacteria. However, production of BGs from gram-positive bacteria remains challenging.

Objective In the present study, we aimed the production of BGs from the gram-positive Weissella kimchii using sodium hydroxide (NaOH), hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3).

Results We generated Weissella kimchii ghosts (WKGs) using the minimum inhibitory concentrations (MIC) of NaOH (3.125 mg/mL), HCl (6.25 mg/mL), H2SO4 (6.25 mg/mL), and HNO3 (12.5 mg/mL). Especially, WKGs induced by NaOH were completely devoid of DNA. We detected the transmembrane lysis tunnel structures in NaOH-induced WKGs using scanning electron microscopy (SEM). We also indicated cell viability of 97.7%. in Raw 264.7 cells (murine macrophages) exposed to the NaOH-induced WKGs at 1 × 105 CFU/mL. Furthermore, the mRNA levels of pro-inflammatory cytokines, such as IL-1β, tumor necrosis factor alpha (TNF-α), inducible nitric oxide synthase (iNOS), and anti-inflammatory cytokine IL-10, were increased by NaOH-induced WKGs in Raw 264.7 cells. Moreover, we investigated the differences in the protein profiles between intact Weissella kimchii and WKGs and evaluated that the levels of 6-phosphogluconate dehydrogenase-like protein and amino acid ABC transporter ATP-binding protein were substantially increased in NaOH-induced WKGs when compared with that of intact Weissella kimchii based on 2DE and MALDI-TOF peptide mass fingerprinting analysis.

Conclusion Our results indicate that NaOH-induced WKGs can be considered as candidates for inactivated bacterial immunostimulants.