Ready or Not: Microbial Adaptive Responses in Dynamic Symbiosis Environments

Abstract

In mutually beneficial and pathogenic symbiotic associations, microbes must adapt to the host environment for optimal fitness. Both within an individual host and during transmission between hosts, microbes are exposed to temporal and spatial variation in environmental conditions. The phenomenon of phenotypic variation, in which different subpopulations of cells express distinctive and potentially adaptive characteristics, can contribute to microbial adaptation to a lifestyle that includes rapidly changing environments. The environments experienced by a symbiotic microbe during its life history can be erratic or predictable, and each can impact the evolution of adaptive responses. In particular, the predictability of a rhythmic or cyclical series of environments may promote the evolution of signal transduction cascades that allow preadaptive responses to environments that are likely to be encountered in the future, a phenomenon known as adaptive prediction. In this review, we summarize environmental variations known to occur in some well-studied models of symbiosis and how these may contribute to the evolution of microbial population heterogeneity and anticipatory behavior. We provide details about the symbiosis between Xenorhabdus bacteria and Steinernema nematodes as a model to investigate the concept of environmental adaptation and adaptive prediction in a microbial symbiosis.

The dynamics between limited-term and lifelong coinfecting bacterial parasites in wild rodent hosts

“…To determine whether each of the observed effects of coinfection on host variables results in facilitation or competition between the parasites would ultimately require measuring the transmission of each parasite to new hosts, to ascertain whether the net direction of the interaction is positive or negative (Ezenwa and Jolles, 2011). The increased instability in the coinfected rodent behavior and physiology is consistent with the expectations for coinfection effects, as multiple infections may disrupt the balance of energy input, use and output within a host (Rynkiewicz et al, 2015) and is likely to negatively affect both parasites (Cao and Goodrich-Blair, 2017). However, their increased body mass gain, for example, may have either positive or negative effects on the parasites, depending on the link between body mass, immune response and resource availability (Hawlena et al, 2005).…”

Legacy of prior host and soil selection on rhizobial fitness in planta

“…Many microbial symbiont populations, including the vast majority of plant‐associated symbionts, experience differences in selection as they alternate between living in soil and host environments (Cao and Goodrich‐Blair ; Martiny and Walters ). Because rhizobia are horizontally transmitted, fluctuating selection can also occur through association with different host genotypes, assuming strain fitness depends on host genotype—as we found here and has been found in other legume‐rhizobia systems (Pahua et al.…”

Acidic pH promotes lipopolysaccharide modification and alters colonization in a bacteria–animal mutualism

“…While sub-lethal exposure to a toxic compound can cue a protective response (Merrell and Camilli, 2002), an unrelated environmental cue from the host (Palmer et al, 2007), other microbes (Ramsey and Whiteley, 2009), or the symbiont population itself (Goo et al, 2012) can also induce a protective response. Such anticipatory switching can evolve when the factors that microbes experience are predictably correlated (Mitchell et al, 2009;Brunke and Hube, 2014;Schwartzman and Ruby, 2016a;Cao and Goodrich-Blair, 2017), and predictive of each other, or where the cue predictably precedes the stress. In both examples, the ability of microbes to predict their future environments requires a period of entrainment and adaptive change.…”