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Recombinant HcGAPDH Protein Expressed on Probiotic Bacillus subtilis Spores Protects Sheep from Haemonchus contortus Infection by Inducing both Humoral and Cell-mediated Responses

By Yi Yang, Guiheng Zhang, Jie Wu, Xueqiu Chen, Danni Tong, Yimin Yang, Hengzhi Shi, Chaoqun Yao, Lenan Zhuang, Jianbin Wang, Aifang Du

Posted 11 Dec 2019
bioRxiv DOI: 10.1101/872291 (published DOI: 10.1128/mSystems.00239-20)

Probiotic Bacillales have been shown effective in controlling pathogens. In particular, live probiotic bacteria are thought to improve the composition of gastrointestinal microbiota, and to reduce pathogen colonization. However, how probiotics regulate immune responses and protect the host from parasitic infection remains largely unknown. In this study, we investigated whether Bacillales can be used against Haemonchus contortus, a parasitic nematode that infects small ruminants in sheep and goats worldwide. Using 16S ribosomal RNA sequencing, we found that Bacillales was highly depleted in the abomasal microbiota of sheep infected with H. contortus. We constructed a recombinant Bacillus subtilis strain (rBSCotB-HcG) that express glyceraldehyde-3-phosphate dehydrogenase of H. contortus (HcGAPDH) on its spore surface. However, mice orally administrated with the rBSCotB-HcG strain showed strong Th1-dominated immune responses; and sheep administrated per os with rBSCotB-HcG showed increased proliferation of peripheral blood mononuclear cells, elevated anti-HcGAPDH IgG levels in sera, and higher anti-HcGAPDH sIgA levels in intestinal mucus. In addition, treatment of H. contortus infected sheep with rBSCotB-HcG (Hc+rBSCotB-HcG) promoted the abundance of probiotic species in the abomasal microbiota; it also improved the average weight gain of the sheep by 27.7%. These Hc+rBSCotB-HcG sheep have reduced number of eggs per gram of feces (by 84.1%) and worm burdens (by 71.5%), with alleviated abomasal damage by H. contortus. Collectively, our data demonstrate the protective roles of CotB-HcGAPDH-expressing B. subtilis spores against H. contortus infection, suggesting a potential value of using this probiotic-based strategy in controlling parasitic nematodes of socioeconomic importance.

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