Genomes of the Neisseria-related symbionts
The complete closed genome of the obligate Hoplopleura acanthopussymbiont, obtained with a combination of Nanopore and Illumina data, is 1 607 498 bp long with 33.4% GC content. It contains 1 421 protein encoding genes, 9 genes coding rRNAs, and 39 genes coding tRNAs (SupplementaryData1). The 9 rRNA genes represent 3 complete 16S-23S-5S rRNA gene operons, but they are arranged in an unlinked manner known from many other bacteria (Brewer et al., 2019), including other P-symbionts (Munson, Baumann, & Baumann, 1993). The 23S rRNA and 5 rRNA genes are placed in close proximity, while the 16S rRNA gene is separated by long stretches of DNA. The genome draft of Polyplax serrata symbiont consisted of 39 contigs which sum to 1 839 042 bp, with the GC content 34.0%. In this assembly, we identified 1 789 protein encoding genes and 37 tRNA genes (SupplementaryData1). Due to the fragmentation of the genome in contigs, the rRNA genes were not reliably assembled and their number remains unclear. To make the following text intelligible, we recategorise Neisseria -related symbionts with the terms “Neisseria”-H (symbiont ofHoploplera ) and “Neisseria”-P (symbiont ofPolyplax ). Genome size and content of these two symbionts, in comparison to other lice symbionts (Riesia spp., Puchtella pedicinophila , Legionella polyplacis , and the symbiont fromProechinophthirus ), Snodgrassella and Neisseria , are summarized in Table 1.
When blasted against the NCBI nr database, a large proportion of the genes in both Neisseria -related symbionts did not yield Neisseriales within the best hits (see Methods and SupplementaryData1). This is in remarkable contrast to Legionella polyplacis , for which 96.3% of the genes were assigned to Legionella by the blast search. However, when compared to each other, the twoNeisseria -related symbionts share a high proportion of their genes and even display a considerable degree of synteny (SupplementaryData1). When aligned with Mauve software the syntenies were placed into 27 Locally Collinear Blocks, the longest blocks extending 100 kb and hundred genes (Figure 1).