Wolbachia, bottled water, and the dark side of symbiosis

Abstract

Obligate endosymbiosis is operationally defined when loss or removal of the endosymbiont from the host results in the death of both. Whereas these relationships are typically viewed as mutualistic, molecular and cellular analysis reveals numerous instances in which these symbiotic relationships are established by alternative, nonmutualistic strategies. The endosymbiont usurps or integrates into core host processes, creating a need where none previously existed. Here I discuss examples of these addictive symbiotic relationships and how they are a likely outcome of all complex evolving systems.

FIGURE 1:

Wolbachia is required for filarial nematode A-P axis formation. (A) Nematode par-1 mutants disrupt A-P axis formation, as evidenced by failed spindle rotation at the two-cell stage. (B) Wild-type and (C) Wolbachia-depleted filarial nematode two-cell stage embryos exhibit normal and failed spindle rotation, respectively. Wolbachia depletion phenocopies par-1 mutant disruption of A-P axis formation. DNA (red) and tubulin (green). Modified from Landmann et al. (2014).

FIGURE 2:

Potential origins of addictive symbiosis. (A) Initial interaction: Symbiont compromises function of key host enzyme. Host response: Compensatory host mutations restore the endosymbiont/enzyme complex to full function. However, proper function of the complex now requires the presence of the endosymbiont. This analogous to the evolutionary rachet mechanism proposed by Gray et al. (2010). (B) Symbiont invades host and is maintained by integrating and becoming essential for a core host cellular or developmental process. By outsourcing essential processes, the host becomes dependent on the presence of the endosymbiont.