The Copy Number of the Operon Determines Pressure Resistance of Endospores.

The operon confers heat resistance to spp., and the resistance correlates to the copy number of the operon. endospores also exhibit a strong variation in resistance to pressure, but the underlying mechanisms of endospore resistance to pressure are not fully understood. We determined the effects of multiple operons on high-pressure resistance in endospores. The copy numbers of the operon in 17 strains of , , , , and were determined via droplet digital PCR (ddPCR) and genome sequencing. These strains contained between 0 and 3 copies of the operon; the quantification of the gene copy number by ddPCR was as accurate as whole-genome sequencing. We further tested the pressure resistance of 17 endospores at 600 MPa and 80°C. Strains with one or no operon had significantly lower pressure resistance than strains with two or three copies of the operons ( < 0.001), indicating that redundant operons in contributed to higher pressure resistance of endospores. The copy number of the operon was not related to the dipicolinic acid (DPA) content of endospores. Overall, the copy number of the operon contributes to pressure resistance of endospores. This improves our understanding of the pressure resistance mechanisms in spp. and may inform the development of high-pressure sterilization in food processing. spp. are considered pressure-resistant microorganisms, but the resistance mechanisms remain unknown. The operon is a mobile genetic element, and it can transfer to pathogenic or spoilage organisms by horizontal gene transfer. Results in this study indicate that multiple copies of the operon mediate high-pressure resistance of endospores, and it might contribute to the identification of the source of pressure-resistant pathogens and spoilage organisms that may contaminate the food supply. The droplet digital PCR (ddPCR) system is well suited for analysis in some human diseases due to its high efficiency and capability to provide high precision; however, no relevant studies in food microbiology have been reported so far. This study demonstrates a novel application of ddPCR in food microbiology.