are required for heterotactic acid fermentation. The enzyme lactate dehydrogenase plays a key role in this process. The genetic process also has ultraviolet radiation protection response, and is associated with the genes recA, lexA, uvrA, uvrB, and uvrC, in addition to a photolyase gene that is expressed when the environment offers excessive ultraviolet radiation stress. Other stress responses include the decomposition of hydrogen peroxide and oxidation. Many Planctomycetota also express sulfatase genes. The genome of Pirellula sp. strain 1 incorporates 110 genes that contribute to encoding proteins that produce sulfatase enzymes. In comparison with a different species of prokaryotic, Pseudomonas aeruginosa, only 6 sulfatases occur and the genes that express these proteins are contained as two to five pairs, usually clustered in 22 groups. Molecular evolution Planctomycetota originate from within the Bacteria and these similarities between proteins in Planctomycetales and eukaryotes reflect convergent evolution. Gained protein families in Gemmataceae, a subgroup within Planctomycetota, have low sequence similarity to eukaryotic proteins; however, they show highest sequence similarity to other Gemmataceae protein families. There is massive emergence of novel protein families within the Gemmataceae. More than one thousand protein families were acquired by duplications and domain rearrangements. The new paralogs function in signal transduction, regulatory systems, and protein interaction pathways. They are related to the functional organisation of the cell, which can be interpreted as an adaptation to a more complex lifestyle. The protein length is longer in the Gemmataceae than in most other bacteria and the genes have linkers. There is an overlap between the longest proteins in Planctomycetales and the shortest proteins in eukaryotes. In the terms of gene paralogy, protein length, and protein domain structures, prokaryotes and eukaryotes do not have sharp boundaries. Phylogeny Originally classified as a eukaryote due to morphology, the advent of genetic sequencing allowed researchers to agree that the Planctomycetota belong to the domain Bacteria. Within that domain, Planctomycetota are classified as their own phylum, however, other researchers have argued they could also be categorized as part of a larger superphylum entitled PVC, which would encompass the phyla Verrucomicrobia, Chlamydiae and Lentisphaerae, and the candidate phylum "Candidatus Omnitrophica". Within this superphylum, its members have been found to be closely related through the creation of 16S rRNA trees. Both the Planctomycetota and Chlamydiota encode proteins for nucleotide transporters, and the Verrucomicrobiota have also been found to have features common among eukaryotic cells. Thus, a common ancestor