Safety Assessment of a Protein-Rich Postbiotic Derived From Methylorubrum extorquens XC23: A 90-Day Feeding Study in Rats and Associated Genotoxicity Assessment

Methylorubrum extorquens XC23 is amutant strain derived from Methylorubrum extorquens PA1 that has been subjected to UV irradiation. This strain primarily utilizes one-carbon compounds as its sole carbon source. It is capable of producing protein-rich biomass, making it an environmentally sustainable alternative protein source compared to conventional proteins derived from both animals and plants. A protein-rich postbiotic derived from Methylorubrum extorquens XC23 (Mea™) was used in a 90-day dietary safety study conducted on Sprague–Dawley rats. The purpose of this study was to evaluate the potential toxicity of the substance and to determine a no-observed-adverse-effect level (NOAEL). In this study, the feed was prepared containing 0%, 4%, 8%, and 16% (total crude protein provided from Mea™ expressed as a percentage of total mass of feed) Mea™, with the corresponding dietary levels of 0, 77, 154, and 308 g/kg, respectively. All animals reached their scheduled sacrifice points without any recorded mortality, and there were no incidents of moribund conditions or unscheduled sacrifices. Additionally, no toxic effects were observed, and no specific target organs were identified. Consequently, Mea™ has a NOAEL of 16.82 and 18.72 g·kg⁻¹·day⁻¹ for male and female rats, respectively. A series of three genotoxicity tests (bacterial reversion mutation test, mammalian erythrocyte micronucleus test, and mouse spermatocyte chromosomal aberration test) showed no evidence of point mutation and chromosome damage.