Serotonin is an important neurotransmitter that plays a role in mood, digestion, sleep, memory and other functions in humans. However, serotonin is not exclusive to humans – it can also be produced by certain bacteria.
Serotonin Production in Bacteria
While serotonin is most well-known for its role in the human brain, it was first discovered not in humans but in serum by Italian scientist Vittorio Erspamer in the 1930s. Further research revealed that serotonin is produced by various organisms, including certain bacteria.
Specific types of bacteria that can produce serotonin include:
- Escherichia coli
- Enterococcus faecalis
- Staphylococcus aureus
- Candida albicans
- Streptococcus pyogenes
- Lactobacillus
- Bacillus
These bacteria produce serotonin through the shikimate pathway, converting the amino acid tryptophan into 5-hydroxytryptophan and then serotonin. The serotonin can then be used for signaling between bacteria cells.
Serotonin’s Role in Bacteria
Research indicates that bacteria produce serotonin to help coordinate various cellular processes and behaviors. Some key roles of serotonin in bacteria include:
- Cell-to-cell communication – Serotonin allows bacteria cells to communicate and coordinate gene expression and group behaviors.
- Growth and replication – Serotonin helps regulate bacterial cell growth and replication rates.
- Virulence – In some pathogenic bacteria, serotonin is thought to contribute to virulence by suppressing the immune response.
- Biofilm formation – Serotonin helps some bacteria stick together and form biofilms on surfaces.
- Spore formation – Serotonin production is linked to sporulation in Bacillus subtilis.
Additionally, recent research indicates that serotonin produced by gut bacteria may play a role in gastrointestinal motility, immunity, and mood regulation in humans through the gut-brain axis.
Research on Bacteria-Produced Serotonin
Ongoing research is further elucidating the specific genes, enzymes, and pathways involved in bacterial serotonin production. Key areas of focus include:
- Characterizing the tryptophan hydroxylase enzymes used to convert tryptophan to 5-HTP.
- Understanding regulation of bacterial tryptophan hydroxylase and serotonin production.
- Exploring serotonin receptor diversity in different bacterial species.
- Examining connections between gut microbiome serotonin and the brain.
Major techniques used in this research area include genetic analysis, metabolomics, high-performance liquid chromatography, immunocytochemistry, and gene knockouts.
Notable Studies on Serotonin Production in Bacteria
Study | Key Findings |
---|---|
Lyte M, Frank CD. Production of an Autoinducer of Growth by Salmonella typhimurium. Microbial Ecology in Health and Disease. 1996. | Showed AI-2 production and response system in Salmonella typhimurium involves serotonin signaling. |
Walters M, et al. Microbial Endocrinology: Host-Bacteria Communication Within the Gut Microbiome. Frontiers in Neuroscience. 2018. | Reviewed role of serotonin and other neurotransmitters in host-microbe cross-talk. |
Tsavkelova EA, et al. Identification and Functional Characterization of Tryptophan Hydroxylase (TPH) in Enterobacteriaceae Family: Prospects for Microbial Synthesis of Serotonin. Applied Microbiology and Biotechnology. 2007. | First characterization of bacterial TPH in E. coli able to synthesize serotonin. |
Conclusion
In summary, serotonin production is not unique to humans and animals – many species of bacteria also synthesize serotonin through the shikimate pathway. Serotonin signaling enables bacteria to coordinate cellular processes and group behaviors. Ongoing research continues to uncover the specific serotonin synthesis mechanisms in different bacteria and the role this neurotransmitter plays in microbe-host interactions, particularly within the human gut microbiome.