Abstract
BackgroundMicrobial cell factories are widely used in the production of acidic products such as organic acids and amino acids. However, the metabolic activity of microbial cells and their production efficiency are severely inhibited with the accumulation of intracellular acidic metabolites. Therefore, it remains a key issue to enhance the acid tolerance of microbial cells. In this study, we investigated the effects of four ATP-binding cassette (ABC) transporters on acid stress tolerance in Lactococcus lactis.ResultsOverexpressing the rbsA, rbsB, msmK, and dppA genes exhibited 5.8-, 12.2-, 213.7-, and 5.2-fold higher survival rates than the control strain, respectively, after acid shock for 3 h at pH 4.0. Subsequently, transcriptional profile alterations in recombinant strains were analyzed during acid stress. The differentially expressed genes associated with cold-shock proteins (csp), fatty acid biosynthesis (fabH), and coenzyme A biosynthesis (coaD) were up-regulated in the four recombinant strains during acid stress. Additionally, some genes were differentially expressed in specific recombinant strains. For example, in L. lactis (RbsB), genes involved in the pyrimidine biosynthetic pathway (pyrCBDEK) and glycine or betaine transport process (busAA and busAB) were up-regulated during acid stress, and the argG genes showed up-regulations in L. lactis (MsmK). Finally, we found that overexpression of the ABC transporters RbsB and MsmK increased intracellular ATP concentrations to protect cells against acidic damage in the initial stage of acid stress. Furthermore, L. lactis (MsmK) consistently maintained elevated ATP concentrations under acid stress.ConclusionsThis study elucidates the common and specific mechanisms underlying improved acid tolerance by manipulating ABC transporters and provides a further understanding of the role of ABC transporters in acid-stress tolerance.
Highlights
Microbial cell factories are widely used in the production of acidic products such as organic acids and amino acids
Overexpression of ATP-binding cassette (ABC) transporters improves acid‐stress tolerance of L. lactis To evaluate the acid stress tolerance of the ABC transporters, four genes were overexpressed in L. lactis NZ9000 (Table 2)
We can conclude that overexpression of the four ABC transporters can confer acid stress tolerance on L. lactis
Summary
Microbial cell factories are widely used in the production of acidic products such as organic acids and amino acids. As a microbial cell factory, Lactococcus lactis is a highly useful bacterial species that is capable of producing chemicals, including lactic acid and vitamins, and is used for fermented foods. It shows stable fermentation performance and phage resistance, and contributes to flavor development [1]. The development of systems biology has accelerated our understanding of mechanisms underlying improved acid tolerance [13]. Based on this novel method, various anti-acid components have been identified, and reverse metabolic engineering approaches have been employed to improve acid resistance
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