Abstract: Disclosed herein are data indicating that specific gut commensal bacteria, and metabolites thereof, can mitigate the outcome of high dose total body irradiation. Based on this, provided herein are methods of mitigating and/or preventing side effects from radiation therapy using short chain fatty acid producing bacterium or metabolites thereof. Cancer and tumor treatments and adjuvant therapies are also provided. Methods of treating and/or mitigating damage to a hematopoietic and/or gastrointestinal system in a subject are also provided using the disclosed adjuvant therapeutic compositions.