Poribacteria

Poribacteria are a candidate phylum of bacteria originally identified in the microbiome of sea sponges (Porifera). Poribacteria were distinguished from other microorganisms associated with sea sponges by their distinctive morphology featuring a large membrane-bound cellular compartment that frequently contains DNA, a highly unusual feature for a prokaryote. Poribacteria are Gram-negative mixotrophs.

Single-cell genomics analysis of poribacteria reveals a genome with a lower size bound of 1.88 megabases and 1585 protein-coding genes, of which an unusually high 24% have no homology to known genes. Among the genes of identifiable homology, genetic infrastructure can be identified for aerobic metabolism, denitrification and urea uptake, and carbon fixation through the Wood-Ljungdahl pathway.

The poribacterial genome is also reported to contain an unusually high number of phyH-domain proteins, which are enzymes involved in oxidative reactions. The functional significance of this observation is not known.

Cell compartmentalization into distinct membrane-bound organelles is a universal and defining property of eukaryotes, but had not been not observed in prokaryotes other than the Planctomycetes before the identification of Poribacteria. The distinctive poribacterial compartments were originally identified using fluorescence in situ hybridization and electron microscopy and were found to frequently, but not always, contain DNA. Genomic evidence reveals the presence of proteins associated with compartmentalization, but not of membrane coat proteins.

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