SYMBIOTIC FACTORS IN Burkholderia ESSENTIAL FOR ESTABLISHING AN ASSOCIATION WITH THE BEAN BUG, Riptortus pedestris

Abstract

Symbiotic bacteria are common in insects and intimately affect the various aspects of insect host biology. In a number of insect symbiosis models, it has been possible to elucidate the effects of the symbiont on host biology, whereas there is a limited understanding of the impact of the association on the bacterial symbiont, mainly due to the difficulty of cultivating insect symbionts in vitro. Furthermore, the molecular features that determine the establishment and persistence of the symbionts in their host (i.e., symbiotic factors) have remained elusive. However, the recently established model, the bean bug Riptortus pedestris, provides a good opportunity to study bacterial symbiotic factors at a molecular level through their cultivable symbionts. Bean bugs acquire genus Burkholderia cells from the environment and harbor them as gut symbionts in the specialized posterior midgut. The genome of the Burkholderia symbiont was sequenced, and the genomic information was used to generate genetically manipulated Burkholderia symbiont strains. Using mutant symbionts, we identified several novel symbiotic factors necessary for establishing a successful association with the host gut. In this review, these symbiotic factors are classified into three categories based on the colonization dynamics of the mutant symbiont strains: initiation, accommodation, and persistence factors. In addition, the molecular characteristics of the symbiotic factors are described. These newly identified symbiotic factors and on-going studies of the Riptortus-Burkholderia symbiosis are expected to contribute to the understanding of the molecular cross-talk between insects and bacterial symbionts that are of ecological and evolutionary importance.

Genome wide association study reveals plant loci controlling heritability of the rhizosphere microbiome

“…In particular, three of these orders, Verrucomicrobiales, Burkholderiales, and Planctomycetales were significantly enriched in the heritable fraction of our dataset. As members of Burkholderiales can form symbioses with both plant and animal hosts 31,32 , and some colonize specific members of a host genus or species 33 , it is feasible that such strong relationships necesitated additional genetic discrimination between hosts. Within Burkholderia spp., this could be facilitated by their relatively large pan-genome, with diversity driven by large multi-replicon genomes and abundant genomic islands 34 .…”

Burkholderia gut symbionts enhance the innate immunity of host Riptortus pedestris

“…Reflecting its free-living origin in the environment, Burkholderia symbiont is easily cultivable 68 on standard microbiological media and consequently amenable to genetic manipulation. The 69 genetically manipulated symbiont strains have been used to understand molecular mechanism of 70 symbiotic association (Kim and Lee, 2015 Hemolymph was collected from the insects that were injected with E. coli as described above. Around 113 To address the question whether the host's systemic immunity can be affected by gut symbiosis, the 152 survival rates of Riptortus hosts harboring Burkholderia symbiont (symbiotic insects) and lacking 153…”

Bacterial cell motility ofBurkholderia gut symbiont is required to colonize the insect gut

“…When host insect fitness and developmental rates were compared between insects harboring Burkholderia gut symbiont and Burkholderia-absent apo-symbiont insects, the beneficial consequences were observed on the host insect by the presence of gut symbiont [4]. These features of the Riptortus-Burkholderia gut symbiotic system provided good opportunities to study insect symbiosis at molecular and biochemical levels [6][7][8][9][10][11][12][13][14][15].…”