| Lactococcus lactis subsp.lactis(L.lactis)is known as industrial starter in the dairy and meat products fermentation,and it plays an important role in human health as an edible probiotic.During industrial production,L.lactis often experiences different stresses that delay the growth and decrease the survival in some serious conditions.Therefore,it is important to understand the stress response of lactic acid bacteria(LAB)under different environmental stresses and its molecular regulation mechanism to reduce the damage caused by various stresses and improve the survival rate of L.lactis.Hydroxypropyl ?-cyclodextrin(HPCD)is widely used in the pharmaceutical excipients because of its high aqueous solubility and stabilizing drug molecules,which have lipophillic inner cavity and hydrophilic outer region.CDs are usually used as pharmaceutical excipients to enable the lipophillic drug to form noncovalent inclusion complex.However,rare study is focused on the effect of HPCD under stress conditions of probiotic bacteria,especially LAB.In this study,HPCD was applied on L.lactis under different stresses,aiming to get a general protective agent for this microorganism.The results would be beneficial for application of L.lactis during industrial production.In this study,the protective effects of hydroxy propyl ?-cyclodextrin(HPCD)on L.lactis CICC6242 under multiple stresses were investigated.The microbial cells were treated with different stresses including heat,Na Cl,cold and H2O2 stresses,and the results were showed by measuring the OD600 or spot plating method.The scanning electron microscopic and fluorescence spectrum were conducted to verify the protective effect.The results showed that the growth and tolerance were improved when HPCD was added during different stress conditions,better than that of trehalose.Besides,the scanning electron microscopic and fluorescence spectrum results showed that HPCD could combine with L.lactis to protect the cell structure.In addition,the experiment further explored the changes of the metabolome of L.lactis under UV stress.Metabolomics analysis was performed on continuous UV irradiation for 4.5min and intermittent UV irradiation for 4.5min(30s interval 30s).The metabolome of L.lactis CICC6242 was sequenced,and the differential metabolites obtained were analyzed biologically.The results showed that a total of 2823 metabolites were detected after UV stress.Compared with the control group,there were 340 differential metabolites in the continuous irradiation group,including 181 up-regulated and 159 down-regulated metabolites;there were 325 differential metabolites in the intermittent irradiation group,including 161 up-regulated and 164 down-regulated metabolites.Besides,there were 39 metabolic pathways affected by continuous irradiation group and 44 metabolic pathways affected by intermittent irradiation compared with the control group.A total of 30 affected pathways were the same between continuous irradiation group and intermittent irradiation group,including secondary metabolite synthesis,antibiotic synthesis,amino acid biosynthesis and so on.This subject studied the protective effects of hydroxypropyl ?-dextrin on L.lactis under various stress conditions,and analyzed the effects of UV stress treatment on the metabolome of L.lactis,which could clarify the effects of metabolites on strain resistance.It provided a certain theoretical basis for the new protective agents in lactic acid bacteria industry. |
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