10.10

Microbial Interactions: Predation

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Microbial predation is the process by which a microbe kills and consumes another to gain nutrients.

Some predatory bacteria are described as epibiotic or endobiotic based on their strategies.

Epibiotic predators like Vampirococcus attach to the prey’s outer membrane, secrete lytic enzymes, and absorb released cytoplasmic material.

Endobiotic predators, like Bdellovibrio, initiate their life cycle by attaching to a prey cell and penetrating its outer membrane to enter the periplasmic space.

Once inside, the predator converts the host into a spherical bdelloplast. It then elongates and replicates, lysing the host to release progeny.

Myxococcus can prey on other microbes but also grows saprotrophically on organic matter.

During predation, coordinated Myxococcus populations use gliding motility to approach and swarm over prey, releasing enzymes and antibiotics that lyse the prey cells.

Predatory protozoans graze on bacteria, helping transfer carbon and energy up the food web.

To defend against grazing, bacteria often form larger structures like filaments, microcolonies, or biofilms.

Overview

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Microbial predation refers to the process by which one microorganism kills and consumes another to obtain nutrients and energy. It encompasses both bacterial and protozoan predators. This interaction plays a crucial role in shaping microbial communities and regulating nutrient cycling.

Bacterial Predators: Epibiotic vs. Endobiotic

Bacterial predators are classified based on their mode of attack as either epibiotic or endobiotic. Epibiotic predators, such as Vampirococcus, attach to the surface of prey cells and secrete hydrolytic enzymes, such as proteases and nucleases, that lyse the host cell, releasing cytoplasmic contents for nutrient absorption. In contrast, endobiotic predators like Bdellovibrio bacteriovorus initiate their life cycle by attaching to the outer membrane of a prey cell and penetrating into the periplasmic space. Within the periplasmic space, the predator elongates and replicates, ultimately lysing the host cell to release multiple progeny.

Facultative Predation by Myxococcus

Myxococcus xanthus, a facultative bacterial predator, alternates between scavenging organic matter and actively preying on other microbes. Employing gliding motility, coordinated myxococcal populations swarm toward and engulf their prey. These swarms secrete a suite of degradative enzymes and secondary metabolites, including antimicrobial compounds such as myxovirescin and myxalamide, that help lyse prey cells and inhibit competitors. This cooperative behavior exemplifies social predation among bacteria and is regulated by cell signaling mechanisms.

Protozoan Grazing and Bacterial Defense

Predatory protozoans—primarily heterotrophic flagellates and ciliates—graze on bacterial populations through phagocytosis. These protozoa play an essential ecological role by transferring carbon and energy up the microbial food web. In response, bacteria often adopt defensive strategies such as forming elongated filaments, clustered microcolonies, or complex biofilms. These structural adaptations provide physical protection and reduce the accessibility of individual cells, making it more difficult for protozoans to engulf or penetrate bacterial targets, thereby enhancing survival under grazing pressure.

Transcript

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Microbial Predation

Bacterial Predators

Epibiotic Predation

Endobiotic Predation

Myxococcus Xanthus

Protozoan Grazing

Bacterial Defense

Gliding Motility

Social Predation