Alicyclobacillus suci produces more guaiacol in media and has duplicate copies of vdcC compared to closely related Alicyclobacillus acidoterrestris.

Some species of the genus Alicyclobacillus cause spoilage in juices and other beverages due to the production of guaiacol, a phenolic compound, and off-aroma. However, little is known about the genomic determinants of guaiacol production across the genus. In this study, we found that several of the genes significantly enriched in guaiacol-producing Alicyclobacillus spp. are associated with oxidative stress response, including vdcC, a phenolic acid decarboxylase putatively responsible for guaiacol synthesis. The food industry recognizes Alicyclobacillus acidoterrestris as the primary guaiacol-producing species found in beverages, though that species was recently split into two closely related yet genetically distinct species, Alicyclobacillus suci and A. acidoterrestris. We found that strains of A. suci (63.0 ± 14.2 ppm) produced significantly (P < 0.01) more guaiacol on average in media than did strains of A. acidoterrestris (25.2 ± 7.0 ppm). Additionally, A. suci and Alicyclobacillus fastidiosus genomes each had duplicate copies of vdcC, while only a single copy of vdcC was found in the genomes of A. acidoterrestris, Alicyclobacillus acidiphilus, and Alicyclobacillus herbarius. Although the food industry has not historically differentiated between A. suci and A. acidoterrestris, it may be increasingly important to target the species with greater spoilage potential. Therefore, we also demonstrated that sequencing a single locus, such as the full-length 16S region or rpoB, is sufficient to differentiate between A. acidoterrestris and A. suci.

Importance: Microbial spoilage increases food waste. To address that challenge, it is critical to recognize and control those microbial groups with the greatest spoilage potential. Non-specific targeting of broad microbial groups (e.g., the genus of Alicyclobacillus) in which only some members cause food spoilage results in untenable, overly broad interventions. Much of the food industry does not differentiate between guaiacol-producing and non-guaiacol-producing Alicyclobacillus species. This is overly broad because Alicyclobacillus spp. which cannot produce guaiacol can be present in beverages without causing spoilage. Furthermore, no distinction is made between Alicyclobacillus suci and Alicyclobacillus acidoterrestris because A. suci is newly split from A. acidoterrestris and most of the food industry still considers them to be the same. However, these findings indicate that A. suci may have greater spoilage potential than A. acidoterrestris due to differences in their genomic determinants for guaiacol production.