Molting-associated suppression of symbiont population and up-regulation of antimicrobial activity in the midgut symbiotic organ of the Riptortus–Burkholderia symbiosis

Carrion beetles in the genus Nicrophorus rear their offspring on decomposing carcasses where larvae are exposed to a diverse community of decomposer bacteria. Parents coat the carcass with antimicrobial secretions prior to egg hatch (defined as prehatch care) and also feed regurgitated food, and potentially bacteria, to larvae throughout development (defined as full care). Here, we partition the roles of prehatch and posthatch parental care in the transmission and persistence of culturable symbiotic bacteria to larvae. Using three treatment groups (full care, prehatch care only, and no care), we found that larvae receiving full care are predominantly colonized by bacteria resident in the maternal gut while larvae receiving no care are colonized with bacteria from the carcass. More importantly, larvae receiving only prehatch care were also predominantly colonized by maternal bacteria; this result indicates that parental treatment of the carcass, including application of bacteria to the carcass surface, is sufficient to ensure symbiont transfer even in the absence of direct larval feeding. Later in development, we found striking evidence that pupae undergo an aposymbiotic stage, after which they are recolonized at eclosion with bacteria similar to those found on the molted larval cuticle and on the wall of the pupal chamber. Our results clarify the importance of prehatch parental care for symbiont transmission in Nicrophorus vespilloides and suggest that these bacteria successfully outcompete decomposer bacteria during larval and pupal gut colonization.IMPORTANCE Here, we examine the origin and persistence of the culturable gut microbiota of larvae in the burying beetle Nicrophorus vespilloides. This insect is particularly interesting for this study because larvae are reared on decomposing vertebrate carcasses, where they are exposed to high densities of carrion-decomposing microbes. Larvae also receive extensive parental care in the form of carcass preservation and direct larval feeding. We find that parents transmit their gut bacteria to larvae both directly, through regurgitation, and indirectly via their effects on the carcass. In addition, we find that larvae become aposymbiotic during pupation but are recolonized apparently from bacteria shed onto the insect cuticle before adult eclosion. Our results highlight the diverse interactions between insect behavior and development on microbiota composition. They further suggest that competitive interactions mediate the bacterial composition of Nicrophorus larvae together with or apart from the influence of beetle immunity, suggesting that the bacterial communities of these insects may be highly coevolved with those of their host species.KEYWORDS Nicrophorus, parental care, symbiosis, microbiota, transmission A nimals are colonized by a diverse community of bacterial symbionts that play crucial roles in their ecology and evolution (1-3). This has been especially well studied in insects, whose bacterial symbionts can influence traits ranging from mate

Section: Discussionsupporting

confidence: 78%

Section: Discussionsupporting

confidence: 72%

Gut Microbiota Colonization and Transmission in the Burying Beetle Nicrophorus vespilloides throughout Development

Wang

Rozen

2017

Appl Environ Microbiol

“…M4 Lysate Preparation-The lysate of M4 midguts of symbiotic and aposymbiotic insects was prepared as described previously with some modifications (25). Twenty samples of the M4 region were dissected from fifth-instar nymphs and homogenized in 100 l of PB with a pestle.…”

Section: Methodsmentioning

confidence: 99%

Insect Gut Symbiont Susceptibility to Host Antimicrobial Peptides Caused by Alteration of the Bacterial Cell Envelope

Son

Journal of Biological Chemistry

et al. 2015

Self Cite

Background:The elucidation of molecular changes of symbionts is important for understanding symbiotic adaptation. Results: Insect gut symbionts are highly susceptible to host immunity because of dramatic cell envelope changes. Conclusion: Cell envelope changes in gut symbionts are required for successful symbiosis with hosts. Significance: Biochemical analyses of intact gut symbionts revealed a novel mechanism of gut symbiosis.

“…The genetically manipulated symbiont strains can then easily be introduced into the host insects via feeding (5)(6)(7)(8). Because newly hatched R. pedestris nymphs are aposymbiotic, symbiotic and aposymbiotic insect lines are easily established by controlling the feeding of the Burkholderia cells (6,9,10). These features show the practicality of the Riptortus-Burkholderia symbiotic system for studying the complex cross talk that occurs between insects and symbiotic bacteria at the molecular and biochemical levels.…”

mentioning

confidence: 95%

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

Kwon

et al. 2014

Appl Environ Microbiol

Self Cite

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.