Tryptamine accumulates in cheese mainly via the decarboxylation of tryptophan by lactic acid bacteria

Few microorganisms are known to decarboxylate L-tryptophan, thereby producing tryptamine, a neuromodulator biogenic amine (BA) that can accumulate in cheese. Since lactic acid bacteria (LAB) are largely responsible for the production of other BA in this product, it was hypothesised that they would also be the main agents of tryptamine production. Using a rapid test based on the natural fluorescence of tryptamine, thousands of bacterial isolates from several cheese samples were screened. Only 1.4% of all isolates (43 out of 2982) were able to synthesise tryptamine and secrete it into the culture medium, highlighting the rarity of tryptophan-decarboxylating activity in this food source. Moreover, over 90% of these isolates were identified as belonging to Loigolactobacillus coryniformis, Enterococcus durans, or the Latilactobacillus sakei group (all lactic acid bacteria). No strain belonging to either of the first two species has previously been described as a tryptamine producer. Strains of the non-LAB species Staphylococcus epidermidis, Klebsiella pneumonia and Corynebacterium flavescens were also identified as tryptamine producers for the first time. Further typification of the producers based on their tryptamine yield was performed, and their potential applications as technological adjuncts for use in the dairy industry, as cell factories, or even as psychobiotics, are discussed.