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Prevalence and Diversity Analysis of Candidate Prophages to Provide An Understanding on Their Roles in Bacillus Thuringiensis

1,2,†, 1,†, 1,3,* and 1,*
1
Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China
2
University of Chinese Academy of Sciences, Beijing 100039, China
3
Present address: State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, Haikou 571158, China
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Viruses 2019, 11(4), 388; https://doi.org/10.3390/v11040388
Received: 3 February 2019 / Revised: 4 April 2019 / Accepted: 24 April 2019 / Published: 25 April 2019
(This article belongs to the Special Issue Diversity and Evolution of Phage Genomes)
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Abstract

Bacillus thuringiensis (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 Siphoviridae 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. View Full-Text
Keywords: Bacillus thuringiensis; prophage; phage; superinfection exclusion; antibiotic resistance gene Bacillus thuringiensis; prophage; phage; superinfection exclusion; antibiotic resistance gene
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Fu, Y.; Wu, Y.; Yuan, Y.; Gao, M. Prevalence and Diversity Analysis of Candidate Prophages to Provide An Understanding on Their Roles in Bacillus Thuringiensis. Viruses 2019, 11, 388.

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