Abstract
The demand for alternatives to antibiotics to improve the growth performance of food animals is increasing. Defensins constitute the first line of defence against pathogens in the innate immune system of animals and humans. A transgenic Chlorella ellipsoidea strain producing mNP-1 (a mutated rabbit defensin NP-1) was previously obtained in our laboratory. In this study, a process for producing the transgenic strain on a large scale was developed, and the C. ellipsoidea strain producing mNP-1 was used as a feed additive to improve the health and growth performance of chickens. The volume of C. ellipsoidea producing mNP-1 can be scaled up to 10,000 L with approximately 100 g/L dry biomass, and the mNP-1 content of transgenic microalgal powder (TMP) was 90–105 mg/L. A TMP-to-regular feed ratio of 1‰, as the optimal effective dose, can promote the growth of broiler chickens by increasing weight by 9.27–12.95%. mNP-1 can improve duodenum morphology by promoting long and thin villi and affect the microbial community of the duodenum by increasing the diversity and abundance of beneficial microbes. These results suggested that transgenic Chlorella producing mNP-1 can be industrially produced and used as an effective feed additive and an alternative to antibiotics for improving the health and growth performance of broiler chickens or other types of food animals/poultry.
Highlights
Antibiotics have traditionally been used as growth promoters at sub-therapeutic levels to enhance food animal growth performance and stabilize their health status[1,2]; antibiotic-resistant microorganisms occur in food-producing animals fed with growth-promoting levels of antibiotics and can be transmitted from animals to the human microbiota[3]
The technology for industrial mNP-1 preparation was developed by large-scale culturing of transgenic C. ellipsoidea expressing mNP-1
The transgenic C. ellipsoidea strain was cultured in a 10-m3 fermenter, and a dry biomass of 90–105 g/L was achieved (Fig. 1)
Summary
Antibiotics have traditionally been used as growth promoters at sub-therapeutic levels to enhance food animal growth performance and stabilize their health status[1,2]; antibiotic-resistant microorganisms occur in food-producing animals fed with growth-promoting levels of antibiotics and can be transmitted from animals to the human microbiota[3]. AMPs target a broad spectrum of organisms with antibiotic resistance, such as bacteria, yeasts, fungi, viruses or parasites[2], and are referred to as ‘host defence peptides’, emphasizing their additional immunomodulatory activities in higher eukaryotic organisms[5,6]. Microalgae are unicellular eukaryotic organisms with a high growth rate, low growth costs, a short culture period and metabolic pathways similar to those of higher plant cells. They are regarded as a new bioreactor that is becoming more attractive in the production of biologically active substances, such as vaccines, antibodies, enzymes, blood-clotting factors, immune regulators, growth factors and hormones[16]. The mechanism by which mNP-1 improved chicken health was further investigated by histological dissection and 16S rRNA-based analysis of the gut microflora
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