The Paradigms They Are a-Changin': past, present and future of PVC bacteria research

Abstract

These are exciting times for PVC researchers! The PVC superphylum is composed of the bacterial phyla Planctomycetes, Verrucomicrobia, Chlamydiae (those three founders giving it its name), Lentisphaerae and Kirimatiellaeota as well as some uncultured candidate phyla, such as the Candidatus Omnitrophica (previously known as OP3). Despite early debates, most of the disagreements that surround this group of bacteria have been recently resolved. In this article, we review the history of the study of PVC bacteria, with a particular focus on the misinterpretations that emerged early in the field and their resolution. We begin with a historical perspective that describes the relevant facts of PVC research from the early times when they were not yet termed PVC. Those were controversial times and we refer to them as the "discovery age" of the field. We continue by describing new discoveries due to novel techniques and data that combined with the reinterpretations of old ones have contributed to solve most of the discordances and we refer to these times as the "illumination age" of PVC research. We follow by arguing that we are just entering the "golden age" of PVC research and that the future of this growing community is looking bright. We finish by suggesting a few of the directions that PVC researches might take in the future.

Keywords: Candidatus Omnitrophica; Chlamydiae; Evolutionary cell biology; Kirimatiellaeota; Lentisphaerae; Planctomycetes; Verrucomicrobia.

Fig. 1

Timeline of the major events in PVC research. A zoom in the decades between 1990 and present is shown

Fig. 2

Phylogenetic representation of the PVC superphylum based on 16S rRNA gene sequences and rooted on the Escherichia coli K12 sequence [adapted from (Spring et al. 2016)]. This tree is supported by RpoB protein based phylogenies and by the phylogenetic composition of the genomes of several representative species. Although still putative, this is the current most complete and comprehensive tree of the PVC superphylum

Fig. 3

Publication and genome numbers for the PVC phyla a Planctomycetes, b Lentisphaera and c Verrucomicrobia (from Alexandru Dan Corlan. Medline trend: automated yearly statistics of PubMed results for any query, 2004. Web resource at URL: http://dan.corlan.net/medline-trend.html). Chlamydiae is not represented due to the huge number of hits related to their pathogenicity. d The number of genomes projects as currently recensed at NCBI genomes (https://www.ncbi.nlm.nih.gov/genome/browse/) is displayed