Growth/toxin-producing temperatures and comprehensive genomic dissection of two toxigenic Burkholderia gladioli pv. cocovenenans strains isolated from dried Auricularia auricula

The foodborne pathogen Burkholderia gladioli pv. cocovenenans ( B. cocovenenans ) produces the lethal mitochondrial toxin bongkrekic acid (BA). To more accurately assess the toxin production levels of toxigenic strains, it is necessary to further optimize the culture conditions used during laboratory detection procedures. Here, we characterized the temperature-dependent growth and BA production of two BA-producing B. cocovenenans strains isolated from commercially available dried Auricularia auricula ( A. auricula ) in China, and examined their genomic relationships to previously reported strains. Across the discrete temperatures tested, both isolates showed the highest biomass at 31 °C and the highest measured BA levels at 37 °C, respectively. These observations are specific to the two isolates and the experimental conditions used; they should not be interpreted as species-wide temperature optima. Whole-genome sequencing, phylogenetic analysis, and average nucleotide identity (ANI) analysis showed that the isolates were closely related to outbreak-associated strains, including Co14, and both carried a bon biosynthetic gene cluster. However, BA levels in the original dry products and bacterial growth or BA production after rehydration were not assessed in this study. The findings therefore support further investigation of temperature-dependent BA production and the occurrence of toxigenic B. gladioli pv. cocovenenans in dried edible fungi, but do not by themselves establish the magnitude of consumer risk or demonstrate that current surveillance procedures underestimate it.