The global scale of livestock farming continues to expand, resulting in shortages of conventional feed protein sources like soybean meal and fishmeal^[1]. Competition over grain between animals and humans has occurred, while livestock rearing and processing can also pollute water and soil^[2]. There is an increasing need to find alternative unconventional proteins to address the shortage of protein resources in animal husbandry. Developing substitute proteins is an effective approach to resolving the lack of feed protein and sustaining the livestock industry.

 

 

Ball-and-stick model of phytic acid. Image from Wikimedia

 

Phytic acid is the storage form of phosphorus in plant seeds, comprising 75% of total seed phosphorus^[3]. Some animals cannot digest phytic acid since they lack phytase enzymes to break it down, resulting in reduced phosphorus bioavailability^[4]. Phytases are naturally present in plants, microbes, and some animal tissues. They catalyze the hydrolysis of phytic acid into inorganic phosphate and lower phosphorylated derivatives, thus enhancing phosphorus digestibility^[5]. Although found in fungi and bacteria, phytases are typically produced in yeast form for commercial use. Feed phytases improve phytate phosphorus bioavailability through phytate hydrolysis.

 

 

Saccharomyces cerevisiae, SEM image. Image from Wikimedia

 

Considering the negative impacts of undigested phytic acid on livestock nutrition, improved methods to degrade phytate are needed to maintain animal health and productivity. We used the generally recognized food-safe yeast Saccharomyces cerevisiae as the host and adopted yeast cell surface display technology to fuse the phytase gene with a cell wall anchor protein gene for expression^{[6, 7]}. Moreover, we tested the phytase activities for thermal stability across feed processing temperatures and activities across animal digestive pH ranges. This generated yeast single-cell protein with phytase activity, which can be added to feed to enhance animal nutrition and absorption.

 

We hope the yeast displaying surface-anchored phytase can directly serve as an affordable feed additive to improve livestock nutrient assimilation, promote growth, and enhance meat quality. This would increase productivity and economic value for the animal husbandry and feed industries.

 

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[2] Menendez E, Garcia-Fraile P. Plant probiotic bacteria: solutions to feed the world [J]. AIMS microbiology, 2017, 3(3): 502-24.

[3] Raboy V. Low phytic acid Crops: Observations Based On Four Decades of Research [J]. Plants-Basel, 2020, 9(2): 140.

[4] Pramitha J L, Rana S, Aggarwal P R, et al. Diverse role of phytic acid in plants and approaches to develop low-phytate grains to enhance bioavailability of micronutrients [M]//KUMAR D. Advances in Genetics, Vol 107. 2021: 89-120.

[5] Dersjant-Li Y, Dusel G. Increasing the dosing of a Buttiauxella phytase improves phytate degradation, mineral, energy, and amino acid digestibility in weaned pigs fed a complex diet based on wheat, corn, soybean meal, barley, and rapeseed meal [J]. Journal of Animal Science, 2019, 97(6): 2524-33.

[6] Dujon B. The yeast genome project: what did we learn? [J]. Trends in genetics, 1996, 12(7): 263-70.

[7] Georgiou G, Stathopoulos C, Daugherty P S, et al. Display of heterologous proteins on the surface of microorganisms: From the screening of combinatorial libraries to live recombinant vaccines [J]. Nature Biotechnology, 1997, 15(1): 29-34.