Genome analysis of new Blattabacterium spp., obligatory endosymbionts of Periplaneta fuliginosa and P. japonica

Abstract

The successful adaptation of cockroaches is, in part, dependent of the activity of their obligatory endosymbionts, Blattabacterium spp., which are involved in uric acid degradation, nitrogen assimilation and nutrient provisioning. Their strategic localization, within bacteriocytes in the proximities of uric acid storage cells (urocytes), highlights their importance in the recycling of nitrogen from urea and ammonia, end-products not secreted by their host insects. In this study, we present the complete genome sequence of two new Blattabacterium spp. from Periplaneta fuliginosa (BPfu) and P. japonica (BPja), and detailed comparison with other Blattabacterium strains from different cockroach species. The genomes of BPfu and BPja show a high degree of stability as showed with for other Blattabacterium representatives, only presenting a 19-kb fragment inversion between BPja and BPfu. In fact, the phylogenomics showed BPja as an ancestor species of BPfu, BPLAN (P. americana) and BBor (Blatta orientalis), in congruence with their host cockroach phylogeny. Their functional profile is similar and closest to the omnivorous strain BBge (Blattella germanica). Interesting, BPja possesses the complete set of enzymes involved sulfate assimilatory pathway only found in BBge and BMda (Mastotermes darwiniensis). The newly sequenced genomes of BPja and BPfu emphasise the remarkable stability of Blattabacterium genomes supported by their long-term coevolution and obligatory lifestyle in their host insect.

Fig 1. Phylogenomics analysis of 75 Bacteroidetes including Blattabacterium strains.

Fig 2. Gene order comparison between all Blattabacterium strains.

Lines between genomes connect orthologous genes in blue if genes are in the same orientation, or in green if they are inverted. The first gene in all strains is yidC (membrane protein insertase C).

Fig 3. COG frequency heat map of different Blattabacterium strains with their pan- and core-genome, and the free-living Capnocytophaga canimorsu.

By alphabetic order: C, energy production and conversion; D, cell cycle control; E, amino acid transport and metabolism; F, nucleotide transport and metabolism; G, carbohydrate transport and metabolism; H, coenzyme transport and metabolism; I, lipid transport and metabolism; J, translation; K, transcription; L, replication, recombination, and repair; M, cell/wall membrane biogenesis; N, cell motility; O, post-translational modification, protein turnover, chaperones; P, inorganic ion transport and metabolism; Q, secondary metabolites biosynthesis, transport, and catabolism; R, general function prediction only; S, function unknown; T, signal transduction mechanism; U, intracellular trafficking and secretion; and V, defense mechanism.

Fig 4. List of genes associated with amino acid synthesis in all sequenced Blattabacterium strains.

The absent genes are represented by white boxes. Host species abbreviations: BPfu, Periplaneta fuliginosa; BPja, Periplaneta japonica; BNCIN, Nauphoeta cinerea; BGIGA, Blaberus giganteus; BBge, Blattella germanica; BPLAN, Periplaneta americana; BBor, Blatta orientalis; BPAA, Panesthia angustipennis; BCpu, Cryptocercus punctulatus; BMda, Mastotermes darwiniensis. Vertical bars indicate omnivorous (blue), wood-feeding (red), and litter-feeding (black) hosts, respectively. EAA are indicated by orange horizontal bars, and non-EAA indicated by black horizontal bars.

Fig 5. The pathway of sulfate assimilation from different Blattabacterium strains.

(a). Genes required for sulfur assimilation (b) include cysN and cysD coding for two subunits of sulfate adenyltransferase; the adenosine 5’-phosphosulfate (APS) reductase cysH and the sulfite reductase cysIJ. There is a missing step for the conversion of adenosine-5'-phosphosulfate (APS) into 3'-phospho adenosine-5'-phosphosulfate (PAPS). The generated sulfite is reduced to hydrogen sulfide further on assimilated into sulfur-containing amino acids L-cysteine and L-methionine.

Fig 6

Reconstruction of pathways for biosynthesis of vitamins (a) and cofactors (b) in Periplaneta fuliginosa and P. japonica. Gene names are indicated in coloured rectangles. White rectangles indicate missing genes and circles indicate products.