What is "gracilicutes"

Gracilicutes ( Latin: gracilis, slender, and cutis, skin, referring to the cell wall) is a controversial taxon in bacterial taxonomy.

Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of molecular phylogeny, the Kingdom Monera (as the domains Bacteria and Archaea were known then) was divided into four phyla,

• Gracilicutes ( gram-negative, it is split in many groups, but some authors stil use it in a narrower sense)
• Firmacutes [sic] ( gram-positive, subsequently corrected to Firmicutes, today it includes the Mollicutes but excludes the Actinobacteria)
• Mollicutes (gram variable, posteriorly renamed as Tenericutes, e.g. Mycoplasma)
• Mendosicutes (uneven gram stain, "methanogenic bacteria" now known as methanogens and classed as Archaea)

This classification system was abandoned in favour of the three-domain system based on molecular phylogeny started by C. Woese.

This taxon was revived in 2006 by Cavalier-Smith as an infrakindgom containing the phyla Spirochaetae, Sphingobacteria, Planctobacteria, and Proteobacteria. However, this taxon is not generally accepted and the three-domain system is followed.

It is a gram-negative clade that branched off from other bacteria just before the evolutionary loss of the outer membrane or capsule, and just after the evolution of flagella.