The copy number of the spoVA2mob operon determines pressure resistance of Bacillus endospores

Abstract

The spoVA2mob operon confers heat resistance to Bacillus spp., and the resistance correlates to the copy number of the operon. Bacillus 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 spoVA2mob operons on high-pressure resistance in Bacillus endospores. The copy numbers of the spoVA2mob operon in 17 strains of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus cereus, Bacillus velezensis, and Bacillus pumilus were determined via droplet digital PCR (ddPCR) and genome sequencing. These strains contained between 0 and 3 copies of the spoVA2mob 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 Bacillus endospores at 600 MPa and 80°C. Strains with one or no spoVA2mob operon had significantly lower pressure resistance than strains with two or three copies of the operons (P < 0.001), indicating that redundant spoVA2mob operons in Bacillus contributed to higher pressure resistance of endospores. The copy number of the spoVA2mob operon was not related to the dipicolinic acid (DPA) content of endospores. Overall, the copy number of the spoVA2mob operon contributes to pressure resistance of Bacillus endospores. This improves our understanding of the pressure resistance mechanisms in Bacillus spp. and may inform the development of high-pressure sterilization in food processing.