Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China.
University of Chinese Academy of Sciences, Beijing 100039, China.
Viruses. 2019 Apr 25;11(4):388. doi: 10.3390/v11040388.
(Bt) is widely used in producing biological insecticides. Phage contaminations during Bt fermentation can cause severe losses of yields. Lots of strategies have been engaged to control extrinsic phage contamination during Bt fermentation, but their effectiveness is low. In this study, the candidate endogenous prophages (prophages) in 61 Bt chromosomes that had been deposited in GenBank database were analyzed. The results revealed that all chromosomes contained prophage regions, and 398 candidate prophage regions were predicted, including 135 putative complete prophages and 263 incomplete prophage regions. These putative complete prophages showed highly diverse genetic backgrounds. The inducibility of the prophages of ten Bt strains (4AJ1, 4BD1, HD-1, HD-29, HD-73, HD-521, BMB171, 4CC1, CT-43, and HD-1011) was tested, and the results showed that seven of the ten strains' prophages were inducible. These induced phages belonged to the family and exhibited a broad host spectrum against the non-original strains. The culture supernatants of the two strains (BMB171, 4CC1) could lyse Bt cells, but no virions were observed, which was speculated to be caused by lysin. The functional analysis of the putative complete prophage proteins indicated that some proteins, such as antibiotic resistance-associated proteins and restriction endonucleases, might increase the fitness of the Bt strains to different environments. The findings of this study provided understanding on the high prevalence and diversity of Bt prophages, as well as pointed out the role of prophages in the life cycle of Bt.
（Bt）被广泛用于生产生物杀虫剂。噬菌体污染在 Bt 发酵过程中会导致产量的严重损失。许多策略已经被用来控制 Bt 发酵过程中的外来噬菌体污染，但它们的效果很低。在这项研究中，对已存入 GenBank 数据库的 61 条 Bt 染色体中的候选内源性原噬菌体（原噬菌体）进行了分析。结果表明，所有染色体都含有原噬菌体区域，预测了 398 个候选原噬菌体区域，包括 135 个推定完整的原噬菌体和 263 个不完整的原噬菌体区域。这些推定完整的原噬菌体显示出高度多样化的遗传背景。测试了 10 株 Bt 菌株（4AJ1、4BD1、HD-1、HD-29、HD-73、HD-521、BMB171、4CC1、CT-43 和 HD-1011）的原噬菌体的诱导性，结果表明这 10 株中的 7 株原噬菌体可诱导。这些诱导噬菌体属于科，对非原始菌株表现出广泛的宿主谱。两个菌株（BMB171、4CC1）的培养上清液可以裂解 Bt 细胞，但没有观察到病毒粒子，这被推测是由溶菌酶引起的。推定完整原噬菌体蛋白的功能分析表明，一些蛋白，如抗生素抗性相关蛋白和限制内切酶，可能会增加 Bt 菌株对不同环境的适应性。本研究的发现提供了对 Bt 原噬菌体高流行率和多样性的理解，并指出了原噬菌体在 Bt 生命周期中的作用。
