Chapter 27: Microbial Interactions – Symbiosis & Competition

The provided chapter, "27 Microbial Interactions" from Prescott's Microbiology 11th Edition, defines and exemplifies the intricate web of relationships that exist between microorganisms and other life forms, often establishing ecosystems known as metaorganisms, holobionts, or superorganisms. The chapter classifies stable associations, or symbiosis, based on whether they are beneficial, neutral, or detrimental to the partners. Two-way positive interactions include mutualism, which is an obligatory relationship where both partners rely on each other for survival (exemplified by aphids and Buchnera aphidicola, or the deep-sea Riftia tube worms and their chemolithotrophic endosymbionts). A related non-obligatory interaction is cooperation (such as the Xenorhabdus nematophila bacterium and its nematode host, Steinernema carpocapsae). Essential metabolic partnerships, like those found in the rumen ecosystem and syntrophy (specifically interspecies hydrogen transfer, where methanogens remove H2 to allow energetically difficult fermentation reactions), demonstrate how microbes rely on each other to process materials. One-way interactions include commensalism, where one organism benefits and the host is unaffected (e.g., initial colonizers facilitating biofilm formation), and amensalism, where one organism harms another via secreted compounds (e.g., antibiotic production or the use of Pseudonocardia by attine ants to control parasitic fungi). Finally, antagonistic interactions cover predation, where the predator kills the prey for resources (Vampirococcus or swarming Myxococcus), parasitism, where the microbe exploits a living host for long-term maintenance (often resulting in genomic reduction, as seen in lichens), and competition for shared resources, which often results in one population dominating the environment, as described by the competitive exclusion principle.