Characterization of Microbial Communities from the Alimentary Canal of Typhaea stercorea (L.) (Coleoptera: Mycetophagidae)

Abstract

The gut microbiomes of symbiotic insects typically mediate essential functions lacking in their hosts. Here, we describe the composition of microbes residing in the alimentary canal of the hairy fungus beetle, Typhaea stercorea (L.), at various life stages. This beetle is a post-harvest pest of stored grains that feeds on fungi and serves as a vector of mycotoxigenic fungi. It has been reported that the bacterial communities found in most insects' alimentary canals contribute to nutrition, immune defenses, and protection from pathogens. Hence, bacterial symbionts may play a key role in the digestive system of T. stercorea. Using 16S rRNA amplicon sequencing, we examined the microbiota of T. stercorea. We found no difference in bacterial species richness between larvae and adults, but there were compositional differences across life stages (PERMANOVA:pseudo-F_(8,2) = 8.22; p = 0.026). The three most abundant bacteria found in the alimentary canal of the larvae and adults included Pseudomonas (47.67% and 0.21%, respectively), an unspecified genus of the Enterobacteriaceae family (46.60 % and 90.97%, respectively), and Enterobacter (3.89% and 5.75%, respectively). Furthermore, Pseudomonas spp. are the predominant bacteria in the larval stage. Our data indicated that field-collected T. stercorea tended to have lower species richness than laboratory-reared beetles (Shannon: H = 5.72; p = 0.057). Furthermore, the microbial communities of laboratory-reared insects resembled one another, whereas field-collected adults exhibited variability (PERMANOVA:pseudo-F_(10,3) = 4.41; p = 0.006). We provide evidence that the environment and physiology can shift the microbial composition in the alimentary canal of T. stercorea.

Keywords: 16S rRNA amplicon sequencing; Typhaea stercorea; alimentary canal; bacterial symbionts; fungivore.

Figure 1

Different life stages of T. stercorea, including their alimentary canal. (A) Late instar larva. (B) Adult. (C) Alimentary canal of late instar larva. (D) Alimentary canal of adult.

Figure 2

Alpha diversity between laboratory-reared larva and adult T. stercorea gut microbiota. A p-value of ≤ 0.05 was used to indicate significant differences between groups. NS denotes non-significant differences between the groups. N denotes the sample size. (A) Species richness boxplot. (B) Pielou’s evenness boxplot. (C) Chao 1 Index boxplot. (D) Shannon Index boxplot. For each group, the bars delineate the means, the hinges represent the lower and upper quartiles, the whiskers extend to the most extreme values, and black dots (●) denote outliers are plotted if present.

Figure 3

Beta diversity between laboratory-reared T. stercorea larva and adult gut microbiota composition. (A) Jaccard PCoA graph showing PCoA1 (0.31 variation) and PCoA2 (0.22 variation). (B) Bray–Curtis PCoA graph showing PCoA1 (0.95 variation) and PCoA2 (0.02 variation). (C) Unweighted UniFrac PCoA graph showing PCoA1 (0.36 variation) and PCoA2 (0.25 variation). (D) Weighted UniFrac PCoA graph showing PCoA1 (0.95 variation) and PCoA2 (0.05 variation). Blue triangles (▲) denote larvae and orange circles (●) denote adults.

Figure 4

Gut microbiota composition of T. stercorea. (A) Taxonomy graph comparing the relative abundances of genera present between larva and adult T. stercorea. The 12 most abundant genera are shown. (B) Two-part Venn diagram comparison between laboratory-reared larva and adult of T. stercorea gut microbiota, showing the OTUs shared among life stages: larva (blue) and adult (orange). The numbers in the diagrams represent how many OTUs were unique in life stages or shared between life stages as their areas intersect.

Figure 5

Alpha diversity between laboratory-reared larvae and adults vs. field-collected T. stercorea adults. A p-value of ≤ 0.05 was used to indicate significant differences between groups. ** denotes significant differences between laboratory-reared adult and field-collected adult. *** denotes significant differences between laboratory-reared larva and field-collected adult. NS denotes non-significant differences between groups. N denotes the sample size. (A) Chao 1 Index. (B) Shannon Index. For each group, the bars delineate the means, the hinges represent the lower and upper quartiles, the whiskers extend to the most extreme values, and outliers are plotted if present.

Figure 6

Beta diversity between laboratory-reared T. stercorea larva and adult gut microbiota composition vs. field-collected adult. (A) Jaccard PCoA graph showing PCoA1 (0.48 variation) and PCoA2 (0.25 variation). (B) Bray–Curtis PCoA graph showing PCoA1 (0.56 variation) and PCoA2 (0.21 variation). (C) Unweighted UniFrac PCoA graph showing PCoA1 (0.48 variation) and PCoA2 (0.25 variation). (D) Weighted UniFrac PCoA graph showing PCoA1 (0.49 variation) and PCoA2 (0.21 variation). Blue triangles (▲) denote laboratory-reared larvae, orange circles (●) denote laboratory-reared adults, and green squares (■) denote field-collected adults.

Figure 7

Comparison of laboratory-reared larvae and adults vs. field-collected adult gut microbiota composition of T. stercorea. Taxonomy graph comparing the relative abundance of genera present in T. stercorea. The 12 most abundance genera are shown.