Insect’s intestinal organ for symbiont sorting

The insect order Hemiptera, one of the best-studied insect lineages with respect to bacterial symbioses, still contains major branches that lack comprehensive characterization of associated bacterial symbionts. The Pyrrhocoroidea (Largidae [220 species] and Pyrrhocoridae [ϳ300 species]) is a clade of the hemipteran infraorder Pentatomomorpha. Studies on bacterial symbionts of this group have focused on members of Pyrrhocoridae, but recent examination of species of two genera of Largidae demonstrated divergent symbiotic complexes in these putative sister families. We surveyed the associated bacterial diversity of this group using paired-end Illumina sequencing and targeted Sanger sequencing of bacterial 16S rRNA amplicons of 30 pyrrhocoroid taxa, including 17 species of Largidae, in order to determine bacterial associates and the similarity of associated microbial communities among species. We also used molecular data (4,800 bp in 5 loci, for 57 ingroup and 12 outgroup taxa) to infer a phylogeny of the host superfamily, in order to trace the evolution of symbiotic complexes among Pentatomomorpha species. We undertook multiple lines of investigation (i.e., experimental rearing, fluorescence in situ hybridization microscopy, and phylogenetic and coevolutionary analyses) to elucidate potential transmission routes for largid symbionts. We found a prevalent and specific association of Largidae with Burkholderia strains of the plant-associated beneficial and environmental clade, housed in midgut tubules. As in other distantly related Heteroptera, symbiotic bacteria seem to be acquired from the environment every generation. We review the current understanding of symbiotic complexes within Pentatomomorpha and discuss means to further investigate the evolution and function of these symbioses. IMPORTANCEObligate symbioses with bacteria are common in insects, particularly Hemiptera, in which various forms of symbiosis occur. However, knowledge regarding symbionts remains incomplete for major hemipteran lineages. Thus, an accurate understanding of how these partnerships evolved and changed over millions of years is not yet achievable. We contribute to our understanding of the evolution of symbiotic complexes in Hemiptera by characterizing bacterial associates of Pyrrhocoroidea, focusing on the family Largidae. Members of Largidae are associated with specific symbiotic Burkholderia strains from a different clade than Burkholderia symbionts in other Burkholderia-associated Hemiptera. Evidence suggests that species of Largidae reacquire specific symbiotic bacteria from the environment every generation, which is a rare strategy for insects, with potentially volatile evolutionary ramifications, but one that must have persisted in Largidae and related lineages since their origin in the Cretaceous Period.

Section: Resultsmentioning

confidence: 67%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Phylogenetic Evidence for Ancient and Persistent Environmental Symbiont Reacquisition in Largidae (Hemiptera: Heteroptera)

Gordon

McFrederick

Weirauch

2016

“…Heteropteran stinkbugs have developed highly species-specific associations with individual gut symbionts that are either maternally transmitted or acquired early in development (44)(45)(46). Other insects have established stable relationships with simple gut communities, including honey and bumble bees (47,48) and ants (49).…”

Section: Discussionmentioning

confidence: 99%

The Core Gut Microbiome of the American Cockroach, Periplaneta americana, Is Stable and Resilient to Dietary Shifts

Tinker

Ottesen

2016

117

131

The omnivorous cockroach Periplaneta americana hosts a diverse hindgut microbiota encompassing hundreds of microbial species. In this study, we used 16S rRNA gene sequencing to examine the effect of diet on the composition of the P. americana hindgut microbial community. Results show that the hindgut microbiota of P. americana exhibit a highly stable core microbial community with low variance in compositions between individuals and minimal community change in response to dietary shifts. This core hindgut microbiome is shared between laboratory-hosted and wild-caught individuals, although wild-caught specimens exhibited a higher diversity of low-abundance microbes that were lost following extended cultivation under laboratory conditions. This taxonomic stability strongly contrasts with observations of the gut microbiota of mammals, which have been shown to be highly responsive to dietary change. A comparison of P. americana hindgut samples with human fecal samples indicated that the cockroach hindgut community exhibited higher alpha diversity but a substantially lower beta diversity than the human gut microbiome. This suggests that cockroaches have evolved unique mechanisms for establishing and maintaining a diverse and stable core microbiome. IMPORTANCEThe gut microbiome plays an important role in the overall health of its host. A healthy gut microbiota typically assists with defense against pathogens and the digestion and absorption of nutrients from food, while dysbiosis of the gut microbiota has been associated with reduced health. In this study, we examined the composition and stability of the gut microbiota from the omnivorous cockroach Periplaneta americana. We found that P. americana hosts a diverse core gut microbiome that remains stable after drastic long-term changes in diet. While other insects, notably ant and bee species, have evolved mechanisms for maintaining a stable association with specific gut microbiota, these insects typically host low-diversity gut microbiomes and consume specialized diets. In contrast, P. americana hosts a gut microbiota that is highly species rich and consumes a diverse solid diet, suggesting that cockroaches have evolved unique mechanisms for developing and maintaining a stable gut microbiota. Most insects host simple gut microbial communities, with only a few unique species represented; the reed beetle, honey bee, fruit fly, and gypsy moth all have fewer than 10 species of bacteria in their guts (1). The low complexity of these communities has been attributed to selective pressures dictated by host physiology (2) and the lack of extensive parental contact with offspring in many insects, which offers few opportunities for vertical and social transmission of gut microbes (1, 3). However, certain social and/or gregarious insect species, including cockroaches and their close relatives, the termites, host complex gut communities comprising hundreds of species (1,4,5).The cockroach gut is composed of three compartments: the foregut, midgut, and hindgut. Of the three, ...

“…The secondary symbiont "Candidatus Arsenophonus arthropodicus" of the hippoboscid louse fly Pseudolynchia canariensis was propagated using this biphasic approach (44). The availability of in vitro cultures has provided a platform for examination of the mechanisms underlying insect-bacterium symbiosis (44)(45)(46).…”

Section: Discussionmentioning

confidence: 99%

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

Buss

Boucias

2016

The phloem-feeding Southern chinch bug, Blissus insularis, harbors a high density of the exocellular bacterial symbiont Burkholderia in the lumen of specialized midgut crypts. Here we developed an organ culture method that initially involved incubating the B. insularis crypts in osmotically balanced insect cell culture medium. This approach enabled the crypt-inhabiting Burkholderia spp. to make a transition to an in vitro environment and to be subsequently cultured in standard bacteriological media. Examinations using ribotyping and BOX-PCR fingerprinting techniques demonstrated that most in vitro-produced bacterial cultures were identical to their crypt-inhabiting Burkholderia counterparts. Genomic and physiological analyses of gut-symbiotic Burkholderia spp. that were isolated individually from two separate B. insularis laboratory colonies revealed that the majority of individual insects harbored a single Burkholderia ribotype in their midgut crypts, resulting in a diverse Burkholderia community within each colony. The diversity was also exhibited by the phenotypic and genotypic characteristics of these Burkholderia cultures. Access to cultures of crypt-inhabiting bacteria provides an opportunity to investigate the interaction between symbiotic Burkholderia spp. and the B. insularis host. Furthermore, the culturing method provides an alternative strategy for establishing in vitro cultures of other fastidious insect-associated bacterial symbionts. M any plant-sap-feeding insects harbor exocellular bacterial symbionts in their digestive tracts (1, 2). These symbionts usually colonize specialized regions of the midgut, are transmitted to offspring by egg smearing, symbiont-containing capsules, or coprophagy, and play a role in host insect fitness (3-7). Exocellular symbionts can provide nutrients to supplement the unbalanced diets of their host insects (1, 8-10)m thus conferring fitness advantages (e.g., body size, coloration, development, and growth) (11-13). In addition, these symbionts have been reported to elicit symbiont-mediated plant specialization (14), to modulate plant virus transmission (15, 16), and/or to induce protection against pathogenic gut bacteria (17), protozoan parasites (18), and synthetic insecticides (19). IMPORTANCE An organ culture method was developed to establish in vitro cultures of a fastidiousRecently, Burkholderia spp. have been detected in the lumens of specialized crypts, at the fourth region of the midgut (M4) (Fig. 1), in the Southern chinch bug, Blissus insularis Barber (Hemiptera: Lygaeoidea: Blissidae) (12). This insect, a primary pest of St. Augustinegrass, Stenotaphrum secundatum (Walter) Kuntze (20,21), feeds on the grass phloem, resulting in diminished grass growth, yellowing and brown blade color, and the eventual death of grass patches (22, 23). Investigations of multiple B. insularis field populations demonstrated that complex Burkholderia ribotypes were present within and among the populations (12). The copy number of the Burkholderia 16S rRNA gene increased ...