Bioinformatic Analysis of Genomic and Proteomic Data from Gemmata

Members of the bacterial phylum Planctomycetes have been claimed to have a compartmentalised cell plan, with cell walls lacking peptidoglycan despite being free-living. These theories have been challenged in recent years, and the nature of the planctomycete cell structure is currently under debate. Yet it remains clear that the planctomycete membranes have unique properties, and are thus likely localisations of evolutional innovation. In this study, proteomes and genomes of four planctomycete species from the Gemmata/Tuwongella clade were investigated with the aim to find candidate genes for functional characterisation. Analysis based on full genome sequencing and mass spectrometry revealed 21 proteins unique to the Gemmata/Tuwongella clade that were present in the proteomes of all four species. The gene coding for one of these was found to be organised in an operon, containing an additional four clade-specific genes, likely related to type II secretion. A planctomycete-specific cell surface signal peptide previously not seen in Gemmata was identified in all four species, with proteins found to have the motif indicating that their cell surface has a strong negative charge. Lastly, the study has revealed evidence suggesting that the planctomycetes have a traditional gram-negative cell wall, contradicting the previously proposed proteinaceous cell wall model