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. 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. Bradymonabacteria have unique living strategies that are transitional between the “obligate” and the so-called 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.

中文翻译：

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缓慢单胞菌是一种新型细菌捕食者群体，在盐水环境中具有多种生存策略。


细菌捕食是微生物群落结构和动态的重要选择力。然而，仅报道了有限数量的捕食性细菌，它们的捕食策略和进化适应仍然难以捉摸。我们最近分离出了一组新的细菌捕食者，即缓慢单胞菌，它是 δ-变形菌纲中新慢单胞菌目的代表。与其他细菌捕食者（例如粘球菌目和蛭弧菌目）相比，缓藻目的捕食和生活策略仍然很大程度上未知。根据缓慢单胞菌与 281 种猎物细菌的单独共培养，缓慢单胞菌捕食多种细菌，但对拟杆菌门具有高度偏好。对最近测序的 13 种缓慢单胞菌的基因组分析表明，这些细菌具有明显的代谢缺陷，但它们可以合成许多聚合物，例如多磷酸盐和聚羟基脂肪酸酯。对慢杆菌和猎物共培养物的双转录组分析表明了潜在的接触依赖性捕食机制。与其他 24 种细菌捕食者的比较基因组分析表明，缓慢杆菌具有不同的捕食和生活策略。此外，我们从 1552 个公开的 16S rRNA 扩增子测序样本中鉴定出缓单胞菌目，表明缓单胞菌目在盐水环境中分布广泛且丰富。系统发育分析表明，该顺序可能有六个亚类；每个亚群占据不同的栖息地。缓慢杆菌具有独特的生存策略，可以在“专性”捕食者和所谓的兼性捕食者之间过渡。 因此，我们提出了一个框架，将当前的细菌捕食者分为三类：（i）专性捕食者（完全依赖猎物），（ii）兼性捕食者（兼性捕食者）和（iii）机会性捕食者（独立于猎物） ）。我们的研究结果为缓藻目提供了一个生态和进化框架，并强调了它们在盐分环境中的潜在生态作用。