Bradymonabacteria, a novel bacterial predator with versatile survival strategies in saline environments

Abstract

Background: Bacterial predation is an important selective force for microbial community structure and dynamics. However, only a limited number of predatory bacteria were reported, and their predatory strategies and evolutionary adaption remain elusive. We recently isolated a novel group of bacterial predator, Bradymonabacteria, representative of the novel order Bradymonadales in δ-Proteobacteria. Compared with other bacterial predators (e.g. Myxococcales and Bdellovibrionales), the predatory and living strategies of Bradymonadales remain largely unknown.Results: Bradymonabacteria preyed on diverse bacteria but had a high preference on Bacteroidetes based on individual co-culture of Bradymonabacteria with 281 prey bacteria. 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 co-culture of Bradymonabacteria and prey suggested the potential contact-dependent predation mechanism. Comparative genomic analysis with other 24 bacterial predators indicated Bradymonabacteria had different predatory and living strategies. Furthermore, we extracted Bradymonadales from 1552 public available 16S rRNA amplicon sequencing samples and found that Bradymonadales was widely distributed and highly abundant in saline environments. Phylogenetic analysis showed there may be six proposed subgroups for this order and each subgroup occupied a different habitat. Conclusions: Bradymonabacteria have unique living strategies, which are different from so-called “obligate” or “facultative” predators. We propose a framework to categorize the current bacterial predators into 3 groups: (i) highly prey-dependent predators, (ii) facultative prey-dependent predators, and (iii) prey-independent predators. Our findings provide an ecological and evolutionary framework for Bradymonadales and highlight their potential ecological roles in saline environments.

Lifecycle of a predatory bacterium vampirizing its prey through the cell envelope and S-layer

“…Obligate predatory bacteria exclusively proliferate in a preydependent manner. They do so as endo-or epibiotic predators that feed on the prey's cellular content by growing and proliferating within the periplasmic space of diderm bacteria [4][5][6] , or while attached to the prey cell surface [7][8][9][10][11] , respectively, through mechanisms that remain largely mysterious.…”