Molecular Pathogens 2024, Vol.15, No.4, 170-178 http://microbescipublisher.com/index.php/mp 171 bacteriovorus, are completely dependent on prey for their growth and reproduction. Facultative predators, like Myxococcus xanthus, can survive on prey but also thrive on other nutrient sources. Opportunistic predators, such as Bradymonabacteria, can live independently of prey but will exploit prey when available (Mu et al., 2020). 2.2 Predator-prey interactions at the cellular level Predatory bacteria employ various strategies to interact with and kill their prey. For instance, Bdellovibrio bacteriovorus attaches to the exterior of Gram-negative prey cells, enters the periplasm, and consumes the host's resources before lysing the cell to find new prey. Myxococcus xanthus, on the other hand, secretes antibiotic metabolites and hydrolytic enzymes that lyse prey organisms, releasing nutrients into the extracellular environment (Sydney et al., 2021). These interactions often lead to significant changes in the prey's genome and phenotypic traits, as seen in coevolving communities of Myxococcus xanthus and Escherichia coli (Nair et al., 2019). 2.3 Metabolic adaptations for predation Predatory bacteria have evolved various metabolic adaptations to facilitate their predatory lifestyle. For example, Bradymonabacteria can synthesize polymers like polyphosphate and polyhydroxyalkanoates, which may aid in their survival and predation in saline environments. Myxococcus xanthus produces a range of secondary metabolites, including antibiotics, which are used as predatory weapons. These metabolic capabilities not only support their predatory activities but also allow them to adapt to different environmental conditions. 2.4 Ecological role of predatory bacteria in natural environments Predatory bacteria play a crucial role in shaping microbial community structures and dynamics. They influence the composition and diversity of microbial ecosystems by selectively preying on specific bacteria, thereby controlling bacterial populations and promoting biodiversity. In marine environments, predatory bacteria like Halobacteriovorax are prevalent on coral surfaces and help regulate the microbiome by preying on potential pathogens. Predatory bacteria can transform the landscape of biofilms, affecting the spatial community ecology and assembly processes (Wucher et al., 2021). Their presence and activity are essential for maintaining the balance and health of various ecosystems (Welsh et al., 2015; Pérez et al., 2016). 3 Key Predatory Bacterial Species 3.1 Bdellovibrio bacteriovorus Bdellovibrio bacteriovorus is a small Deltaproteobacterium known for its unique ability to prey on other Gram-negative bacteria. This predatory bacterium has garnered significant attention due to its potential application as a "living antibiotic" to combat antibiotic-resistant pathogens. B. bacteriovorus invades the periplasmic space of its prey, where it digests host resources and proliferates, eventually releasing multiple daughter cells to continue the predation cycle (Figure 1) (Laloux, 2020; Cavallo et al., 2021). Studies have shown that B. bacteriovorus can significantly reduce the viability of microbial communities, such as those found in activated sludge, by altering their composition and reducing biomass (Feng et al., 2017). The bacterium's ability to secrete nucleases during its predatory cycle helps degrade prey DNA, potentially reducing the spread of antibiotic resistance genes (Bukowska-Faniband et al., 2020). The broad host range and the ability to kill many antibiotic-resistant pathogens make B. bacteriovorus a promising candidate for therapeutic applications. 3.2 Myxococcus xanthus Myxococcus xanthus is a well-characterized myxobacterium that preys on a wide range of Gram-negative and Gram-positive bacteria, as well as fungi. This predatory bacterium employs a generalist predatory mechanism involving the secretion of antibiotic metabolites and hydrolytic enzymes, which lyse prey organisms and release nutrients into the extracellular environment (Negus et al., 2017; Findlay et al., 2019). M. xanthus has been studied extensively for its predation strategies and the molecular responses of prey organisms. Research has identified several genes in prey bacteria, such as Pseudomonas aeruginosa, that contribute to resistance against M. xanthus predation. These genes are involved in metal/oxidative stress response, motility, and detoxification of antimicrobial peptides. The broad prey range and the ability to overcome various resistance mechanisms make M. xanthus an important model organism for studying bacterial predation.
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