Purine Biosynthesis, Biofilm Formation, and Persistence of an Insect-Microbe Gut Symbiosis

Abstract

cThe Riptortus-Burkholderia symbiotic system is an experimental model system for studying the molecular mechanisms of an insect-microbe gut symbiosis. When the symbiotic midgut of Riptortus pedestris was investigated by light and transmission electron microscopy, the lumens of the midgut crypts that harbor colonizing Burkholderia symbionts were occupied by an extracellular matrix consisting of polysaccharides. This observation prompted us to search for symbiont genes involved in the induction of biofilm formation and to examine whether the biofilms are necessary for the symbiont to establish a successful symbiotic association with the host. To answer these questions, we focused on purN and purT, which independently catalyze the same step of bacterial purine biosynthesis. When we disrupted purN and purT in the Burkholderia symbiont, the ⌬purN and ⌬purT mutants grew normally, and only the ⌬purT mutant failed to form biofilms. Notably, the ⌬purT mutant exhibited a significantly lower level of cyclic-di-GMP (c-di-GMP) than the wild type and the ⌬purN mutant, suggesting involvement of the secondary messenger c-di-GMP in the defect of biofilm formation in the ⌬purT mutant, which might operate via impaired purine biosynthesis. The host insects infected with the ⌬purT mutant exhibited a lower infection density, slower growth, and lighter body weight than the host insects infected with the wild type and the ⌬purN mutant. These results show that the function of purT of the gut symbiont is important for the persistence of the insect gut symbiont, suggesting the intricate biological relevance of purine biosynthesis, biofilm formation, and symbiosis.

Pathogen-mediated manipulation of arthropod microbiota to promote infection

“…Because A. phagocytophilum colonization reduced the abundance of Gram-positive biofilm-forming species like the Enterococci, we hypothesized that IAFGP alters the tick microbiota by inhibiting bacterial biofilms in the gut. Biofilms have been demonstrated to serve important roles in facilitating pathogen colonization in arthropod intestines (12)(13)(14). To elucidate the importance of IAFGP in shaping the tick gut microbiota, we injected the antibiofilm peptide, P1, derived from IAFGP (25), and showed that this improved A. phagocytophilum infection, in ticks.…”

“…In arthropods, the microbiota is associated with a biofilm, generated from diverse bacterial species. These microbial biofilms are necessary for establishing successful symbiotic relationships with their arthropod hosts (12)(13)(14).…”

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].…”

Culturing and Characterization of Gut Symbiont Burkholderia spp. from the Southern Chinch Bug, Blissus insularis (Hemiptera: Blissidae)

“…Biofilm formation has been reported in other Burkholderia species (Burkholderia pseudomallei and B. cepacia complex species), and it may be associated with many factors, such as nutrient content, osmolarity, oxygen, pH, and temperature (49)(50)(51). In selected microbe-invertebrate symbioses, biofilm formation contributes to the establishment and persistence of symbiotic bacteria in host symbiont organs (52)(53)(54)(55). Biofilms produced by crypt-associated exocellular Burkholderia spp.…”