Chloroflexi (phylum) - History

History

See also: Bacterial taxonomy and Bacterial phyla

In 1987, Carl Woese, regarded as the forerunner of the molecular phylogeny revolution, divided Eubacteria into 11 divisions based on 16S ribosomal RNA (SSU) sequences and grouped the genera Chloroflexus, Herpetosiphon and Thermomicrobium into the "Green non-sulfur bacteria and relatives", which was temporarily renamed as "Chloroflexi" in Volume One of Bergey's Manual of Systematic Bacteriology.

Being a deep branching phylum (cf. Bacterial phyla) its classification was analysed in Volume One of Bergey's Manual of Systematic Bacteriology and included a single class with the same name, the class Chloroflexi. Since 2001 however, new classes have been created thanks to newly discovered species, therefore currently the phylum Chloroflexi is divided into:

• Chloroflexi
• Thermomicrobia
• "Dehalococcoidetes"
• Anaerolineae
• Caldilineae
• Ktedonobacteria

Regarding the class "Dehalococcoidetes", the placeholder name was given by Hugenholtz & Stackebrandt, 2004, after "Dehalococcoides ethenogenes" a partially described species in 1997, whereas the first species fully described was Dehalogenimonas lykanthroporepellens by Moe et al. 2009, but in the description of that species the class was not made official nor were families or orders laid out as the two species share only 90% 16S identity, meaning that they could fall in different families or even orders.

Recent phylogenetic analysis of the Chloroflexi has found very weak support for the grouping together of the different classes currently part of the phylum. The six classes that make up the phylum did not consistently form a well-supported monophyletic clade in phylogenetic trees based on concatenated sequences for large datasets of proteins and no conserved signature indels were identified that were uniquely shared by the entire phylum. However, the classes “Chloroflexi” and Thermomicrobia were found to group together consistently by both the usual phylogenetic means and the identification of shared conserved signature indels in the 50S ribosomal protein L19 and the enzyme UDP-glucose 4-epimerase. It has been suggested that the phylum Chloroflexi “sensu stricto” should comprise only the classes Chloroflexi and Thermomicrobia, and the other four classes (“Dehalococcoidetes,” Anaerolineae, Caldilineae and Ktedonobacteria) may represent one or more independent phyla branching in the neighborhood of the Chloroflexi.