The complete mitochondrial genome of the deep-sea methanotrophic sponges Hymedesmia methanophila and Iophon methanophila: leveraging 'waste' in metagenomic data.

A significant proportion of next-generation sequencing (NGS) data ends up not being used since they comprise information out-of-scope of the primary studies. This 'waste' of potential can be harnessed to explore organellar genomes, such as the mitochondrial DNA, and be used for evolutionary, conservation and biodiversity research. We present the complete mitochondrial genomes of the deep-sea methanotrophic sponges Hymedesmia methanophila and Iophon methanophila (Demospongiae, Poecilosclerida) retrieved from previously published whole metagenome sequencing data. The predicted mitogenome of H. methanophila (18,657 bp) and I. methanophila (18,718 bp) present the characteristic arrangement observed among Poecilosclerida sponges. These mtDNAs encode the usual set of 14 proteins, two ribosomal RNA, and 24 or 23 transfer RNA genes, respectively, with intergenic regions amounting ~5% of their total length. The overall similarity of these mitogenomes to those of phylogenetic relatives, both in organization and divergence, suggests that neither their extremophilic habitat in asphalt seeps within the deep sea nor their symbiotic association with methaneoxidizing bacteria imposed a major influence on the evolution of their mitochondrial genome. This research shows how metagenomic data can be leveraged to extract additional genetic knowledge from primary metagenome sources, and by exploiting previously unexplored sequencing data, valuable information can be unlocked to shed light on the evolutionary dynamics of diverse organisms inhabiting extreme environments.