Stress as a Normal Cue in the Symbiotic Environment

Abstract

All multicellular hosts form associations with groups of microorganisms. These microbial communities can be taxonomically diverse and dynamic, and their persistence is due to robust, and sometimes coevolved, host-microbe and microbe-microbe interactions. Chemical and physical sources of stress are prominently situated in this molecular exchange, as cues for cellular responses in symbiotic microbes. Stress in the symbiotic environment may arise from three sources: host tissues, microbe-induced immune responses, or other microbes in the host environment. The responses of microbes to these stresses can be general or highly specialized, and collectively may contribute to the stability of the symbiotic system. In this review, we highlight recent work that emphasizes the role of stress as a cue in the symbiotic environment of plants and animals.

Keywords: host-microbe interactions; microbiota; stress response; symbiosis.

Figure 1. Three Sources of Stress Define the Host Environment

Host tissues may be a source of chemical and/or physical stress. The presence of tissue-associated stress is not dependent on microbes. Microbes that can grow within the constraints of the host tissues may, themselves, produce stress through competitive or antagonistic interactions. Microbial activity in host tissues, or interactions with specific microbial taxa within the community, may induce immune-associated stress. Abbreviation: ROS; reactive oxygen species.

Figure 2. Host-Microbe Interactions May be Studied at the Level of an Individual Microbial Taxon, or at the Community Level

Examples of model systems for investigating how a single species of microbe colonizes a host: (a) squid-Vibrio fischeri, (b) leach-Aeromonas veronii, (c) nematode-Xenorhabdus spp., (d) legume-Sinorhizobium meliloti, (e) tsetse fly-Sodalis glossinalus, (f) gnotobiotic mouse stomach-Helicobacter pylori, and mouse gut-diverse microbes, (g) stink bug-Burkholderia spp. Tissue sites that have been used to study microbe microbe interactions: (h) skin and (i) teeth. Examples of host that have been used to study microbial communities: (j) the mouse gut, (k) Arabidopsis thaliana, (l) leaf-cutter ants, (m) the bovine rumen, and (n) Hydra vulgaris.