Such ‘psychobiotics’ may alleviate symptoms of excessive stress, anxiety, and depression by affecting physiological outputs and processes in the host such as immune function22, tryptophan metabolism23, corticosterone/cortisol17,24, neurotransmitters25–27, microbial metabolites28, and brain-derived neurotrophic factor (BDNF)29. The gene discussed is BDNF; the disease is Anxiety.