Abstract：
Insect guts offer unique habitats for microbial colonization, with gut bacteria potentially offering numerous benefits to their hosts. Although Enterococcus has emerged as one of the predominant gut commensal bacteria in insects, its establishment in various niches within the gut has not been characterized well. In this study, Enterococcus mundtii was inoculated into the silkworm (Bombyx mori L.) to investigate its biological functions. Genome-based analysis revealed that its successful colonization is related to adherence genes (ebpA, ebpC, efaA, srtC, and scm). This bacterium did not alter the activities of related metabolic enzymes or the intestinal barrier function. However, significant changes in the gene expressions levels of Att2, CecA, and Lys suggest potential adaptive mechanisms of host immunity to symbiotic E. mundtii. Moreover, 16S metagenomics analysis revealed a significant increase in the relative abundance of E. mundtii in the intestines of silkworms following inoculation. The intestinal microbiome displayed marked heterogeneity, an elevated gut microbiome health index, a reduced microbial dysbiosis index, and low potential pathogenicity in the treatment group. Additionally, E. mundtii enhanced the breakdown of carbohydrates in host intestines. Overall, E. mundtii serves as a beneficial microbe for insects, promoting intestinal homeostasis by providing competitive advantage. This characteristic helps E. mundtii dominate complex microbial environments and remain prevalent across Lepidoptera, likely fostering long-term symbiosis between the both parties. The present study contributes to clarifying the niche of E. mundtii in the intestine of lepidopteran insects and further reveals its potential roles in their insect hosts.
摘要：
昆虫内脏为微生物定植提供了独特的栖息地，肠道细菌可能为它们的宿主提供许多好处。尽管肠球菌已成为昆虫中主要的肠道共生细菌之一，它在肠道内各种壁龛中的建立并没有得到很好的表征。在这项研究中,将肠球菌接种到家蚕（BombyxmoriL.）中以研究其生物学功能。基于基因组的分析显示，其成功定植与粘附基因(ebpA，ebpC,efaA,srtC,和SCM）。该细菌没有改变相关代谢酶的活性或肠屏障功能。然而,Att2、CecA、Lys和Lys提出了宿主对共生E.mundtii免疫的潜在适应性机制。此外，16S宏基因组学分析显示，接种后，蚕肠道中E.mundtii的相对丰度显着增加。肠道微生物组表现出明显的异质性，肠道微生物组健康指数升高，微生物菌群失调指数降低，治疗组潜在致病性低。此外,E.mundtii增强了宿主肠道中碳水化合物的分解。总的来说,E.mundtii是昆虫的有益微生物，通过提供竞争优势来促进肠道稳态。这种特征有助于E.mundtii控制复杂的微生物环境，并在鳞翅目中保持流行，可能促进双方之间的长期共生。本研究有助于阐明鳞翅目昆虫肠道中E.mundtii的生态位，并进一步揭示其在昆虫宿主中的潜在作用。
