[Isolation, characterization and real-time RT-PCR for relative quantification of gene expression in...

The aim of this study was to isolate Lactobacillus plantarum acid-sensitive mutants with lower H+-ATPase activity, and to study the mechanism of H+-ATPase regulation in Lactobacillus plantarum.

We used neomycin to isolate acid-sensitive mutants of L. plantarum, and measured H+-ATPase activity and lactic acid production of wild-type and mutants. Genomic DNA was extracted from the wild-type ZUST and two mutants (ZUST-1, ZUST-2), and used as PCR templates. H+-ATPase genes of the strain were amplified, and the PCR products were sequenced. Sequence similarity of H+-ATPase was analyzed. Real-time RT-PCR was used to evaluate the relative quantification of the H+-ATPase genes expression.

The growth of the mutants was characterized in MRS broth, which revealed that their cell biomass and acid production were lower than that of the wild-type. H+-ATPase activity of the mutants ZUST-1 and ZUST-2 was 10.1% and 28.8% lower than that of the wild-type. Results showed that atpA gene of the mutants ZUST-1 and ZUST-2 existed 22 mutations by alignment of the wild-type sequence, and atpC gene of ZUST-2 existed 6 mutations. Mutants ZUST-1 and ZUST-2 atpA gene expression were 41.1% and 35.7% lower than that of the wild-type in exponential phase, 43.6% and 14.2% in stationary phase, respectively. The atpC gene expression of ZUST-1 was similar to that of the wild-type in exponential phase, and was 30% higher than that of the wild-type in stationary phase, and ZUST-2 atpC gene was not expressed.

The mutants with lower H+-ATPase activity were found to up-regulate the expression of H+-ATPase genes in stationary phase, except ZUST-2 atpC gene was not expressed. H+-ATPase activity has an important connection with the difference in gene expression of atpA and atpC. The results of this study will pave the way for gaining further insights into the mechanism of the H+-ATPase-defective mutants.