Stability of potential prophages in commercial strain Lactobacillus plantarum NCU116 under various stressors

Genetic stability of bacterium as a starter culture is vital for product quality in fermentation industry. The commercial strain Lactobacillus plantarum NCU116 widely used in fruit and vegetable fermentation was induced with various stressors to investigate the stability of potential prophages. PHAge Search Tool (PHAST) identified three potential prophages in bacterial genome. By spectrophotometric analysis, mitomycin C (MMC), lactic acid, and bile salt were found to inhibit the growth of L. plantarum NCU116 while ethanol and hydrogen peroxide had no notable impacts. Transcriptions of four phage-synthesizing genes (phaR, phacap, phaada, phatail) and four phage-resistant genes (cas116, helR, hsd1, hsd2) under stressors were investigated by quantitative reverse transcription PCR. MMC was found to most significantly upregulated transcriptions of phage-synthesizing genes, followed by lactic acid and bile salt. By transmission electron microscopy, no virus particles from the lysates of strain NCU116 treated by MMC were observed, corresponding to the result that no phage nucleic acids could be extracted from the supernatants of strain NCU116 treated by MMC. This study suggested that no prophages could be induced from L. plantarum NCU116 by strong inducer MMC, indicating its genetic stability, which supports the comprehensive application of strain NCU116 in industry without causing fermentation failure.