Plastic responses to competition: Does bacteriocin production increase in the presence of nonself competitors?

Abstract

Anticompetitor traits such as the production of allelopathic toxins can confer significant competitive benefits but are often costly to produce. Evolution of these traits may be facilitated by environment‐specific induction; however, the extent to which costly anticompetitor traits are induced by competitors is not well explored. Here, we addressed this question using bacteriocins, which are highly specific, proteinaceous anticompetitor toxins, produced by most lineages of bacteria and archaea. We tested the prediction that bacteriocin production is phenotypically plastic and induced by the presence of competitors by examining bacteriocin production in the presence and absence of nonself competitors over the course of growth of a producing strain. Our results show that bacteriocin production is detectable only at high cell densities, when competition for resources is high. However, the amount of bacteriocin activity was not significantly different in the presence vs. the absence of nonself competitors. These results suggest that bacteriocin production is either (a) canalized, constitutively produced by a fixed frequency of cells in the population or (b) induced by generic cues of competition, rather than specific self/nonself discrimination. Such a nonspecific response to competition could be favored in the natural environment where competition is ubiquitous.

Trade‐off between reproductive and anti‐competitor abilities in an insect–parasitic nematode–bacteria symbiosis

“…However, as seen in our study, if a sensitive strain is not present, grown with and without a competitor (Bhattacharya, Pak, & Bashey, 2018 ). Therefore, when in a non-competitive context, the inhibitors may be paying a cost to produce bacteriocin, but receiving no competitive benefit.…”

“…Within insect production and assemblage of the phage‐like bacteriocin particles has been demonstrated in Xenorhabdus (Morales‐Soto & Forst, ) and may use resources otherwise allocated for killing the insect host or aiding in nematode reproduction. While some bacteria may increase bacteriocin production in response to the presence of competitors, no difference in bacteriocin activity was detected when Xenorhabdus was grown with and without a competitor (Bhattacharya, Pak, & Bashey, ). Therefore, when in a non‐competitive context, the inhibitors may be paying a cost to produce bacteriocin, but receiving no competitive benefit.…”

Evolution of increased virulence is associated with decreased spite in the insect-pathogenic bacterium Xenorhabdus nematophila

“…The inhibitory activity of the bacteriocin extracts derived from the evolved and ancestral lineages were compared using a growth inhibition bioassay [28]. Briefly, a bacteriocin extract (or culture medium in the 'no bacteriocin' controls) and a starting culture of sensitive cells (approx.…”

Microbial warfare and the evolution of symbiosis

“…We suggest that competition through bacteriocins could provide a relatively general explanation why hosts would be selected to increase the relatedness between bacterial symbionts. Empirical work has shown that some bacterial species conditionally upregulate their production of bacteriocins in response to the presence of competing strains [18][19][20]. Consequently, when there are more genetically differentiated lineages, and so relatedness between interacting bacterial symbionts is lower, bacterial symbionts will put more resources into killing each other.…”