Metagenomic and culturomic analyses of bacterial species contributing to tyramine formation in Cheonggukjang

Abstract

This study investigated bacterial compositions and their contributions to biogenic amine (BA) formation in Cheonggukjang using metagenomic and culturomic analyses. Metagenomic analysis revealed Bacillus spp. as dominant (96.19%), of which B. piscis (74.79%) and B. hisashii (19.39%) were predominant. Based on the relative abundance of BA-associated genes, B. piscis showed the highest correlations with tyrosine (R2 = 0.76) and lysine decarboxylation (R2 = 0.50), and B. hisashii with histidine decarboxylation (R2 = 0.42). Meanwhile, culturomic analysis revealed that, among mesophilic bacteria, Bacillus spp. were dominant (98.78%). As lactic acid bacteria (LAB), only Enterococcus spp. were detected. Of halotolerant LAB, Enterococcus spp. were dominant (90.72%). Based on in vitro BA productivity of all bacterial strains, Enterococcus spp. contributed primarily to tyramine formation. Thus, it was observed that the bacterial compositions and their contributions to BA formation determined using the two analyses differed considerably. To verify such observations, Cheonggukjang fermentation experiments were conducted using Bacillus and Enterococcus strains. The tyramine content was higher in the Bacillus-fermented samples (over 120.00 ± 14.18 mg/kg) than in the Enterococcus-fermented sample (34.24 ± 3.37 mg/kg). However, the spermidine and spermine content was higher in the Enterococcus-fermented sample (108.04 ± 6.69 and 22.93 ± 6.28 mg/kg, respectively). Therefore, these two bacterial species may contribute together to BA formation in Cheonggukjang but in slightly different manners.