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.

This work was funded by the Plan for Science, Technology and Innovation of the Principality of Asturias 2018– 2022, co-financed by FEDER (Grant AYUD/2021/50916) and by MCIN/AEI/10.13039/501100011033 (Grant PID2020‐112629RB‐I00). D. A. was the recipient of a predoctoral contract (Grant PRE2021-098772) funded by MCIN/AEI/ 10.13039/501100011033 and by “ESF Investing in your future”. B. S. was the recipient of a research fellowship funded by Agencia Estatal CSIC, JAE Program (Grant JAEINT_23_01684). A. C. was the recipient of an ERASMUS+training grant funded by European Union (2022-PT01-KA131-HED-000052781). The authors acknowledge the assistance of Isabel Cuesta and Carmen Santos from the Chromatography Unit at IPLA-CSIC, and the Unit of Information Resources for Research (URICI-CSIC) via its CSIC Open Access Publication Support Initiative. The authors also thank Adrian Burton for language and editing assistance.

Peer reviewed