Inclusion Criteria:  Diagnosis of pulmonary arterial hypertension (PAH) On stable treatment for PAH for one month prior to enrollment Able to swallow capsultes Able to provide blood sample and fecal sample  Exclusion Criteria:  Dysphagia to pills Clinically active inflammatory bowel disease Pregnancy or breastfeeding Life expectancy of <6 months Presence of ileostomy or colostomy Taking immunosuppressants (calcineurin inhibitors, prednisone greater than or equal to 20mg/day, methotrexate, azathioprine, immunosuppressive biologics, JAK inhibitors) Neurotropenia (an absolute neurotrophil count < 0.5 x 10^9 cells/L) History of solid organ or bone marrow transplant Anticipated recurrent antibiotic use (participants with frequent urinary tract infections or sinusitis) History of severe anaphylactic food allergy History of celiac disease History of receiving cancer chemotherapy, immunotherapy, or radiation