Temperature influences the outcomes of an environmentally-acquired symbiosis

Pentatomomorphan bugs can form symbiotic associations with bacteria
belonging to the supergenus Burkholderia sensu lato. This relationship has
become a model for understanding environmental symbiont acquisition. Host
insects can utilize various symbiont strains from across Burkholderia
sensu lato, however, host colonization success and benefits conferred vary
by bacterial clade. Therefore, we conducted a meta-analysis aimed at
identifying candidate genes that underpin beneficial symbioses within this
system. We scanned the entire Burkholderiaceae family for the presence of
17 colonization-associated genes, as well as 88 candidate genes that are
differentially expressed during symbiosis. There was no difference in the
distribution of the 17 colonization-associated genes between symbiotic
(Caballeronia and iPBE) and non-symbiotic lineages; however, there was a
higher prevalence of the 88 candidate genes in the insect symbiont
lineages. We subsequently analyzed the genomes of nine symbiotic
Caballeronia strains that confer varying fitness benefits to their insect
hosts. One symbiont strain was significantly worse, one was significantly
better, and the remaining seven were intermediate in terms of conferred
host fitness benefits. We found that strains possessing a higher number of
the candidate genes conferred faster host development time. Furthermore,
we identified two candidate genes that were missing in the least
beneficial strain but present in the other eight, suggesting that these
genes may be important in modulating symbiont quality. Our study suggests
that the mechanisms required for host colonization are broadly distributed
across Burkholderiaceae, but the genes that determine symbiont quality are
more prevalent in insect-associated species. This work helps to identify
genes that influence this highly specialized yet diverse symbiosis between
Pentatomomorphan insects and Burkholderiaceae bacteria.