10.10
Interactions microbiennes : prédation
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Q1: What is the difference between epibiotic and endobiotic bacterial predators?
Epibiotic predators like Vampirococcus attach to prey cell surfaces and secrete lytic enzymes to break down the outer membrane, absorbing released cytoplasmic material externally. Endobiotic predators like Bdellovibrio penetrate the prey's outer membrane and enter the periplasmic space, where they replicate before lysing the host cell from within to release progeny.
Q2: How does Myxococcus use cooperative behavior to prey on other microbes?
Myxococcus populations employ gliding motility to coordinate and swarm toward prey cells. These swarms secrete degradative enzymes and antimicrobial compounds that lyse prey cells. This social predation strategy allows coordinated populations to overwhelm and consume other microbes more effectively than individual cells could alone.
Q3: What role do predatory protozoans play in microbial food webs?
Predatory protozoans graze on bacterial populations through phagocytosis, transferring carbon and energy up the microbial food web. This grazing pressure helps regulate bacterial populations and drives nutrient cycling within microbial communities, making protozoans essential components of microbial ecology and ecosystem function.
Q4: How do bacteria defend themselves against protozoan grazing?
Bacteria adopt structural defensive strategies including forming elongated filaments, microcolonies, or biofilms. These larger structures provide physical protection and reduce individual cell accessibility, making it more difficult for protozoans to engulf or penetrate bacterial targets and enhancing survival under grazing pressure.
Q5: What happens inside a prey cell after Bdellovibrio penetrates it?
After Bdellovibrio enters the periplasmic space, it converts the host cell into a spherical structure called a bdelloplast. The predator then elongates and replicates within this protected environment before lysing the host cell membrane to release multiple progeny that can infect new prey cells.
Q6: Can Myxococcus survive without actively preying on other microbes?
Yes, Myxococcus is a facultative predator that can alternate between actively preying on other microbes and growing saprotrophically on organic matter. This metabolic flexibility allows Myxococcus populations to survive in environments where prey availability varies, making them adaptable members of microbial communities.
Q7: What enzymes do epibiotic predators use to break down prey cells?
Epibiotic predators secrete hydrolytic enzymes including proteases and nucleases that lyse host cell membranes and degrade cellular components. These lytic enzymes break down the structural and molecular barriers of prey cells, releasing cytoplasmic contents that the predator can absorb for nutrients and energy.