Identification of biogenic amine-producing microbes during fermentation of ganjang, a Korean traditional soy sauce, through metagenomic and metatranscriptomic analyses

Microbes responsible for producing biogenic amines (BAs) during fermentation of ganjang, a Korean traditional soy sauce, were investigated through metagenomic and metatranscriptomic analyses. BA analysis revealed that cadaverine, putrescine, tyramine, and histamine were generated during ganjang fermentation and BA-producing decarboxylase sequences were searched from metagenomic contigs through BlastP and sequence similarity network analyses. A total of 16 putative BA-producing decarboxylase sequences, including five ornithine decarboxylases (ODC), one lysine decarboxylase (LDC), one histidine decarboxylase (HDC), and nine tyrosine decarboxylases (TDC) were identified and phylogenetically classified. BA-producing gene and expression analysis suggested that cadaverine and histamine might only be produced by the LDC gene of Staphylococcus showing relatively high expression levels and the HDC gene of Tetragenococcus showing very low expression levels, respectively, during the middle fermentation periods. Additionally, putrescine and tyramine might be produced by the ODC and TDC genes, respectively, by various microbes during the entire fermentation period. The analyses also suggested that the ODC genes of Bacillus and Halomonas, expressed at a low level, might be responsible for producing putrescine during early fermentation, while after 60 days the ODC gene of Lactobacillus, expressed at a comparatively high level, might be dominantly responsible for producing putrescine. Additionally, the TDC genes of Bacillus, Enterococcus, and Virgibacillus might be responsible for producing tyramine at 20 and 40 days of fermentation, while after 60 days the TDC gene of Tetragenococcus, which was highly expressed at this time point, along with Virgibacillus and Enterococcus, might be majorly responsible for producing tyramine.