Genome sequence of "Candidatus Walczuchella monophlebidarum" the flavobacterial endosymbiont of Llaveia axin axin (Hemiptera: Coccoidea: Monophlebidae)

Abstract

Scale insects (Hemiptera: Coccoidae) constitute a very diverse group of sap-feeding insects with a large diversity of symbiotic associations with bacteria. Here, we present the complete genome sequence, metabolic reconstruction, and comparative genomics of the flavobacterial endosymbiont of the giant scale insect Llaveia axin axin. The gene repertoire of its 309,299 bp genome was similar to that of other flavobacterial insect endosymbionts though not syntenic. According to its genetic content, essential amino acid biosynthesis is likely to be the flavobacterial endosymbiont's principal contribution to the symbiotic association with its insect host. We also report the presence of a γ-proteobacterial symbiont that may be involved in waste nitrogen recycling and also has amino acid biosynthetic capabilities that may provide metabolic precursors to the flavobacterial endosymbiont. We propose "Candidatus Walczuchella monophlebidarum" as the name of the flavobacterial endosymbiont of insects from the Monophlebidae family.

Keywords: comparative genomics; scale insect; symbiosis; γ-Proteobacteria.

Fig. 1.—

Llaveia axin axin insects. (a) Twenty-day-old nymphs on Jatropha curcas plants, (b) adult females on Jatropha curcas, (c) dissection of left side of abdomen of adult female in a dorsal plane showing the lobed bacteriome (BAC) and ovaries (OV), gut, and malpighian tubules were removed.

Fig. 2.—

Localization of Walczuchella monophlebidarum (green) by fluorescent in situ hybridization in 20-day-old nymphs of Llaveia axin axin. (a) Dorsal tissue sections of the whole body showing the pair of large lobed bacteriomes where flavobacteria reside, (b) sagittal tissue section of the whole body showing one lobed bacteriome, (c) enlarged image of a bacteriome lobe.

Fig. 3.—

Evolutionary relationships of the flavobacterial and enterobacterial symbionts of Llaveia axin axin. (a) Phylogeny from flavobacterial endosymbionts inferred from sequences of the 16S rRNA gene. F indicates the flavobacterial endosymbiont of the respective insect. Sequences from free-living bacteria were used as outgroups. Bootstrap values for 1,000 replicates are shown adjacent to each node, (b) phylogeny from endosymbiotic and free-living enterobacteria inferred from the concatenated amino acid alignment of ten genes using the Maximum Likelihood method based on the Whelan And Goldman + Freq. model. Bootstrap values for 1,000 replicates are shown adjacent to each node. Asterisk indicates the location of the Llaveia axin axin enterobacterial symbiont in the tree.

Fig. 4.—

Left: A metabolic reconstruction of Walczuchella monophlebidarum of Llaveia axin axin based on its genetic content. Right: A representation of the enterobacterial symbiont capabilities for amino acid biosynthesis. Absent genes are shown in red. Pseudogenes are shown in light gray. Green boxes represent essential amino acids. White boxes represent nonessential amino acids.

Fig. 5.—

Genomic alignments of Walczuchella monophlebidarum of Llaveia axin axin (y axis) versus (A) Uzinura diaspidicola (B) Sulcia muelleri CARI, (C) Blattabacterium sp. BPLAN, and (D) Flavobacterium psychrophilum. Forward matches shown in red. Reverse matches shown in blue.