Comparative transcriptome analysis reveals the contribution of membrane transporters to acid tolerance in Lactococcus lactis

Acid stress caused by the accumulation of acidic metabolites severely affects the fermentation performance of lactic acid bacteria. In this study, to overcome the impact of acid stress during growth, nine membrane trans-porters were introduced in Lactococcus lactis NZ9000 to study their effects on acid tolerance. The engineered strains that overexpressed the metal ATP-binding cassette (ABC) transporters zitP (metal ABC transporter permease) and zitQ (metal ABC transporter ATP-binding protein) exhibited 14.5 and 9.5-fold higher survival rates, respectively, at pH 4.0 for 4 h than the control strain. During acid stress, the two recombinant strains maintained relatively higher ATP concentrations, i.e., 7.7-and 11.7-fold higher, respectively, than the control strain at pH 4.0 for 3 h. Subsequently, transcriptome analysis revealed that genes associated with ABC trans-porters, metal ion transport, transcriptional regulation, and stress response exhibited differentially expressed. The transcriptional level of ecfA2 gene (energy-coupling factor transporter ATPase) was substantially higher in L. lactis (ZitQ) during acid stress, and the ecfA2 gene was overexpressed in L. lactis. This recombinant strain L. lactis (EcfA2) exhibited a 598.7-fold higher survival rate than the control strain at pH 4.0 for 4 h. This study showed that the membrane transporters ZitP and ZitQ could increase acid tolerance and provided a strategy for constructing robust strains that can be used in food industry.

Automated summary

This study found that overexpressing the metal ATP-binding cassette (ABC) transporters ZitP and ZitQ can significantly improve the acid tolerance of lactic acid bacteria. Transcriptome analysis revealed differential gene expression related to ABC transporters, metal ion transport, and stress response. The overexpression of the ecfA2 gene (energy-coupling factor transporter ATPase) resulted in an extremely high survival rate during acid stress. This research provides a strategy for constructing robust strains that can be used in the food industry.