Bradymonabacteria, a novel bacterial predator group with versatile survival strategies in saline environments
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RESEARCH
Open Access
Bradymonabacteria, a novel bacterial predator group with versatile survival strategies in saline environments Da-Shuai Mu1,2, Shuo Wang2, Qi-Yun Liang2, Zhao-Zhong Du2, Renmao Tian3, Yang Ouyang3, Xin-Peng Wang2, Aifen Zhou3, Ya Gong1,2, Guan-Jun Chen1,2, Joy Van Nostrand3, Yunfeng Yang4, Jizhong Zhou3,4 and Zong-Jun Du1,2*
Abstract Background: Bacterial predation is an important selective force in microbial community structure and dynamics. However, only a limited number of predatory bacteria have been reported, and their predatory strategies and evolutionary adaptations remain elusive. We recently isolated a novel group of bacterial predators, Bradymonabacteria, representative of the novel order Bradymonadales in δ-Proteobacteria. Compared with those of other bacterial predators (e.g., Myxococcales and Bdellovibrionales), the predatory and living strategies of Bradymonadales are still largely unknown. Results: Based on individual coculture of Bradymonabacteria with 281 prey bacteria, Bradymonabacteria preyed on diverse bacteria but had a high preference for Bacteroidetes. Genomic analysis of 13 recently sequenced Bradymonabacteria indicated that these bacteria had conspicuous metabolic deficiencies, but they could synthesize many polymers, such as polyphosphate and polyhydroxyalkanoates. Dual transcriptome analysis of cocultures of Bradymonabacteria and prey suggested a potential contact-dependent predation mechanism. Comparative genomic analysis with 24 other bacterial predators indicated that Bradymonabacteria had different predatory and living strategies. Furthermore, we identified Bradymonadales from 1552 publicly available 16S rRNA amplicon sequencing samples, indicating that Bradymonadales was widely distributed and highly abundant in saline environments. Phylogenetic analysis showed that there may be six subgroups in this order; each subgroup occupied a different habitat. Conclusions: Bradymonabacteria have unique living strategies that are transitional between the “obligate” and the socalled facultative predators. Thus, we propose a framework to categorize the current bacterial predators into 3 groups: (i) obligate predators (completely prey-dependent), (ii) facultative predators (facultatively prey-dependent), and (iii) opportunistic predators (prey-independent). Our findings provide an ecological and evolutionary framework for Bradymonadales and highlight their potential ecological roles in saline environments. Keywords: Bacterial predator, Bradymonadales, Metabolic deficiencies, Comparative genomic analysis, Biogeographic analysis * Correspondence: [email protected] 1 State Key Laboratory of Microbial Technology, Institute of Microbial Technology, Shandong University, No. 72, Jimo Binhai Road, Jimo, Qingdao 266237, China 2 Marine College, Shandong University, Weihai 264209, China Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
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