Distribution of dominant bacterial taxa
Microbiomes of the tested species/lineages of the lice are dominated by
several bacterial taxa with a complex distribution pattern. For two of
these bacteria, Legionella polyplacis from Polyplax and
Neisseriaceae from Hoplopleura lice, their symbiotic nature could
be clearly demonstrated based on the complete genome characteristics and
distribution within the host. For other bacteria, partial 16S rRNA gene
amplicons provide two (not entirely independent) kinds of information:
taxonomical assignment and GC content. Besides Neisseriaceae, two more
OTUs, identified as dominant taxa (see methods for definition) and
taxonomically assigned to Blochmania and Arsenophonusgenera, were associated with Hoplopleura samples (Figure 2). In
addition to the sequence characteristic (GC content of 43.9% and
49.3%), the distribution of these OTUs among the two Hoplopleuraspecies and H. acanthopus populations points to their symbiotic
nature.
For Polyplax serrata a comprehensive population-wide amplicon
screening revealed (besides L. polyplacis ) 9 dominant taxa
assigned to the genus or family level (Figure 3). The distribution of
OTUs with a low GC content, i.e. Buchnera (45.1% GC) andArsenophonus 2 (49.4% GC), reflects the genealogy of the host
and thus indicates putative obligate coevolving symbionts. For the other
taxa, the taxonomic assignment and GC content >50% (with
the exception of Cloacibacterium ) indicates that the bacteria may
represent environmental contamination or very early symbiotic
associations, e.g. Neisseriaceae taxon and Arsenophonus 1.
However, it is important to note that the taxonomical assignment of the
OTUs are based on a short sequence and should be interpreted as
approximate affiliations rather than precise phylogenetic position,
particularly compared to highly derived genomes like Buchnera andBlochmannia .