A Survey of Phage Contamination in Natto-producing Factories and Development of Phage-resistant Bacillus subtilis (natto) Strains

Abstract

Eight natto-producing factories were surveyed for the contamination of phages that infect Bacillus subtilis (natto). A total of 160 sampling points, including manufacturing pipelines, instruments, floors, drainage ports, containers, and building facilities were inspected by wiping the surfaces. Virulent phages were detected from 28 survey points in four of the factories. Phages were frequently found in factories that had experienced product spoilage by phage contamination within the past 3 years. Isolated phages were not clonal and variations in their genomes were observed, although some phages were very similar. We developed phage-resistant B. subtilis (natto) strains using isolated phages as indicators. They were resistant against all phages found in the survey and those isolated decades ago from spoiled natto. The yueB gene that codes the receptor for phage SPP1 was not essential for the phages tested in this study to infect B. subtilis (natto) strains.