Burkholderia insecticola triggers midgut closure in the bean bug Riptortus pedestris to prevent secondary bacterial infections of midgut crypts

摘要

a–r A GFP-labeled Burkholderia symbiont was orally administered, and the posterior part of the midgut (M2-M4) was observed by epifluorescence microscopy, starting from the time of symbiont inoculation to 72 h after inoculation, just before the 3rd instar molting. Host nuclear DNA was stained by DAPI. The M4B is closed during symbiont infection (a–h) and reopened by backflow of symbiont cells during the colonization of M4 (i–r). M2, midgut second section; M3, midgut third section; M4, midgut fourth section with crypts (symbiotic organ); M4B, M4 bulb; H, hindgut. s Change of the CR width. While the CR width continuously increases in aposymbiotic insects, the CR becomes thinner during 12–18 hpi (arrow). This timing corresponds to the midgut closure event. t Change of the maximum M4B width. After the flow back of symbiont cells from M4 to M4B, occurring around 36–48 hpi, the M4B becomes bulbous. n = 5. Welch’s t test was performed between aposymbiotic and symbiotic insects (**P < 0.05; ***P < 0.005).