Genomics and phylogeny of the proposed phylum ‘ Candidatus Poribacteria’ associated with the excavating sponge Thoosa mismalolli

Members of the proposed phylum ‘ Candidatus Poribacteria’ are among the most abundant microorganisms in the highly diverse microbiome of the sponge mesohyl. Genomic and phylogenetic characteristics of this proposed phylum are barely known. In this study, we analyzed metagenome-assembled genomes (MAGs) obtained from the coral reef excavating sponge Thoosa mismalolli from the Mexican Pacific Ocean. Two MAGs were extracted and analyzed together with 32 MAGs and single-amplified genomes (SAGs) obtained from NCBI. The phylogenetic tree based on the sequences of 139 single-copy genes (SCG) showed two clades. Clade A (23 genomes) represented 67.7% of the total of the genomes, while clade B (11 genomes) comprised 32.3% of the genomes. The Average Nucleotide Identity (ANI) showed values between 66 and 99% for the genomes of the proposed phylum, and the pangenome of genomes revealed a total of 37,234 genes that included 1722 core gene. The number of genes used in the phylogenetic analysis increased from 28 (previous studies) to 139 (this study), which allowed a better resolution of the phylogeny of the proposed phylum. The results supported the two previously described classes, ‘ Candidatus Entoporibacteria’ and ‘ Candidatus Pelagiporibacteria’, and the genomes SB0101 and SB0202 obtained in this study belong to two new species of the class ‘ Candidatus Entoporibacteria’. This is the first comparative study that includes MAGs from a non-sponge host ( Porites lutea ) to elucidate the taxonomy of the poorly known Candidatus phylum in a polyphasic approach. Finally, our study also contributes to the sponge microbiome project by reporting the first MAGs of the proposed phylum ‘ Candidatus Poribacteria ’ isolated from the excavating sponge T. mismalolli .