Bacterial species diversity of family burkholderiaceae colonizing midgut crypts of Riptortus pedestris (Hemiptera: Alydidae)

Riptortus pedestris (Hemiptera: Alydidae) is known to establish symbiotic mutualism by acquiring bacteria in Burkholderiaceae from soil. This environmental acquisition, in general, does not yield high level of physiological links between two organisms; however, R. pedestris is known to establish direct physiological connections with bacterial complex in Burkholderiaceae. Under this circumstance, understanding of bacterial species diversity in R. pedestris is essential to better understand symbiosis between the two organisms. Therefore, this study identified bacterial species acquired by R. pedestris from field-collected soil. In laboratory conditions, 2^nd instar nymphs were provided soil samples and reared to adult. Then, bacteria colonizing midgut crypts were cultured and subject to species identification based on 16S rRNA sequencing analysis. From the experiments, 80% of R. pedestris (n = 51) were found with single bacterial species, whereas 20% were detected with two different bacterial species. Most bacteria belonged to the genus Caballeronia (84%), followed by Paraburkholderia (13%), Burkholderia (2%), and Pandoraea (2%). At species level, a total of 16 species were identified; Caballeronia jiangsuensis (34%) and C. megalochromosomata (18%) were the two most dominant species detected from the insect midguts. Our study reports for the first time the species diversity of bacteria establishing endosymbiosis with R. pedestris in South Korea. This information can serve as basis to better understand evolutionary relationships between the insect host and environmentally-acquired symbiotic microbes. In addition, further study needs to elucidate the ecological effects of those symbionts on R. pedestris such as fitness and behavior of the host.