Safety evaluation of a novel variant of consensus bacterial phytase

Gregory S Ladics; Kang-Hyun Han; Min S Jang; Heejin Park; Valerie Marshall; Yueming Dersjant-Li; Vincent J Sewalt

doi:10.1016/j.toxrep.2020.07.004

Safety evaluation of a novel variant of consensus bacterial phytase

Toxicol Rep. 2020 Jul 15:7:844-851. doi: 10.1016/j.toxrep.2020.07.004. eCollection 2020.

Authors

Gregory S Ladics¹, Kang-Hyun Han², Min S Jang², Heejin Park², Valerie Marshall³, Yueming Dersjant-Li⁴, Vincent J Sewalt⁵

Affiliations

¹ DuPont Nutrition and Biosciences, 200 Powder Mill Road, Wilmington, DE, USA.
² Department of Advanced Toxicology Research, Korea Institute of Toxicology, 141 Gajeong-ro, Yuseong-gu, Daejeon, 34114, Republic of Korea.
³ DuPont Nutrition and Biosciences, 1501 Larkin Center Drive, Midland, Michigan, USA.
⁴ DuPont Animal Nutrition, DuPont Nutrition and Biosciences, Archimedesweg, 30, 2333 CN, Leiden, the Netherlands.
⁵ DuPont Nutrition and Biosciences, 925 Page Mill Road, Palo Alto, CA, 94304, USA.

Abstract

A 90-day subchronic oral toxicity study was conducted to evaluate the safety of a consensus bacterial phytase variant 6-phytase (PhyG) for use as an animal feed additive. This phytase is produced by fermentation with a fungal (Trichoderma reesei) production strain expressing a biosynthetic variant of a consensus bacterial phytase gene assembled via ancestral reconstruction with sequence bias for the phytase from Buttiauxella sp. Rats were administered PhyG daily via oral gavage at dose-levels of 0 (distilled water), 250, 500 or 1000 mg total organic solids (TOS)/kg bodyweight (bw)/day (equivalent to 0, 112,500, 225,000 and 450,000 phytase units (FTU)/kg bw/day, respectively). No test article-related adverse effects were observed. A no-observed-adverse-effect level (NOAEL) for PhyG was established as 1000 mg TOS/kg bw/day, the highest test concentration. Based on this NOAEL and an estimate of broiler consumption determined from the proposed inclusion of the phytase in feed at the maximum recommended level (4000 FTU/kg), a margin of safety value of 1613 was calculated. Results of in vitro genotoxicity testing and in silico protein toxin evaluation further confirmed PhyG to be non-genotoxic and not likely to be a protein toxin upon consumption. These data support the safety of PhyG as an animal feed additive.

Keywords: BLAST, basic local alignment search tool; DM, dry matter; FTU, phytase units; Genetic toxicology; IP6, myo-inositol hexaphosphate; MCP, monocalcium phosphate; NOAEL; NOAEL, no-observed-adverse-effect-level; OECD, The Organisation for Economic Co-operation and Development; Oral gavage; Phytase; SSL, safe strain lineage; Subchronic study; TOS, total organic solids; UFC, ultra-filtered concentrate; bw, body weight.