Joined: Jan. 2003
This page on spiroplasma:
...says that sprioplasmas are related to gram-positive bacteria, and have no cell wall, have a cytoskeleton and membranes with cholesterol. This all seems to go along fairly well with Cavalier-Smith's proposed scheme for the evolution of eukaryotes as something like:
gram-negative --> gram-positive --> early divergence from archaeabacteria --> eukaryotes
I doubt it. Spiroplasma seems to have evolved by regressive evolution from clostridia, so they are not a step forward. Unlike mreb and ftsz, which have actin and tubulin analogs in eukaryotes, fib has no homologs whatsoever.