Some embodiments include bacterial species for use in treatment of one or more autism spectrum disorder (ASD), and/or schizophrenia symptoms in a subject in need thereof. The subject in need thereof can have a gut microbiota signature characteristic of an adult. The bacterial species can include Bacteroides (e.g., B. fragilis, B. thetaiomtaomicron, and/or B. vulgatus), and/or Enterococcus (e.g., E. faecalis, E. faecium, E. hirae, E. avium, E. durans, E. gallinarum, or E. casseliflavus). Upon treatment, one or more ASD-related behaviors can be improved in the subject.