Some embodiments relate to genetically engineered bacterial strains for modulation of levels of the bacterial metabolite 4-ethylphenol (4EP) and its sulfated form, 4-ethylphenyl sulfate (4EPS). In some embodiments, the bacteria reduce or inhibit production of 4EP or 4EPS in the gut of a subject. The bacteria can ameliorate, delay the onset, or reduce the likelihood of one or more symptoms associated with anxiety and/or autism spectrum disorder (ASD) in the subject.