Data from: Expression of eukaryotic-like protein in the microbiome of sponges

Eukaryotic-like proteins (ELPs) are classes of proteins that are found in
prokaryotes, but have a likely evolutionary origin in eukaryotes. ELPs
have been postulated to mediate host-microbiome interactions. Recent work
has discovered that prokaryotic symbionts of sponges contain abundant and
diverse genes for ELPs, which could modulate interactions with their
filter-feeding and phagocytic host. However, the extent to which these ELP
genes are actually used and expressed by the symbionts is poorly
understood. Here we use metatranscriptomics to investigate ELP expression
in the microbiomes of three different sponges (Cymbastella concentrica,
Scopalina sp. and Tedania anhelens). We developed a workflow with
optimized rRNA removal and in silico subtraction of host sequences to
obtain a reliable symbiont metatranscriptome. This showed that between 1.3
and 2.3% of all symbiont transcripts contain genes for ELPs. Two classes
of ELPs (cadherin and tetratricopetide repeats) were abundantly expressed
by in the C. concentrica and Scopalina sp. microbiomes, while ankyrin
repeat ELPs were predominant in the T. anhelens metatranscriptome.
Comparison to non-ELP containing transcripts indicated a constitutive
expression of ELPs across a range of bacterial and archaeal symbionts.
Expressed ELPs also contained domains involved in protein secretion and/or
were co-expressed with proteins involved in extra-cellular transport. This
suggests these ELPs are likely exported, which could allow for direct
interaction with the sponge. Our study shows that ELP genes in sponge
symbionts represent actively expressed functions that could mediate
molecular interaction between symbiosis partners.