WHAT ARE ARCHAEBACTERIA - LIFES 3RD DOMAIN OR MONODERM PROKARYOTES RELATED TO GRAM-POSITIVE BACTERIA - A NEW PROPOSAL FOR THE CLASSIFICATION OF PROKARYOTIC ORGANISMS

Authors
Citation
Rs. Gupta, WHAT ARE ARCHAEBACTERIA - LIFES 3RD DOMAIN OR MONODERM PROKARYOTES RELATED TO GRAM-POSITIVE BACTERIA - A NEW PROPOSAL FOR THE CLASSIFICATION OF PROKARYOTIC ORGANISMS, Molecular microbiology, 29(3), 1998, pp. 695-707
Citations number
39
Categorie Soggetti
Biology,Microbiology
Journal title
ISSN journal
0950382X
Volume
29
Issue
3
Year of publication
1998
Pages
695 - 707
Database
ISI
SICI code
0950-382X(1998)29:3<695:WAA-L3>2.0.ZU;2-K
Abstract
The evolutionary relationship within prokaryotes is examined based on signature sequences (defined as conserved inserts or deletions shared by specific taxa) and phylogenies derived from different proteins. Arc haebacteria are indicated as being monophyletic by a number of protein s related to the information transfer processes, In contrast, for seve ral other highly conserved proteins, common signature sequences are pr esent in archaebacteria and Gram-positive bacteria, whereas Gram-negat ive bacteria are indicated as being distinct. For these proteins, arch aebacteria do not form a phylogenetically distinct dade but show polyp hyletic branching within Gram-positive bacteria. A closer relationship of archaebacteria to Gram-positive bacteria in comparison with Gram-n egative bacteria is generally seen for the majority of the available g ene/protein sequences. To account for these results and the fact that both archaebacteria and Gram-positive bacteria are prokaryotes surroun ded by a single cell membrane, I propose that the primary division wit hin prokaryotes is between monoderm prokaryotes (surrounded by a singl e membrane) and diderm prokaryotes (i.e. all true Gram-negative bacter ia containing both an inner cytoplasmic membrane and an outer membrane ). This proposal is consistent with both cell morphology and signature sequences in different proteins, The monophyletic nature of archaebac teria for some genes, and their polyphyletic branching within Gram-pos itive bacteria as suggested by others, is critically examined, and sev eral explanations, including derivation of archaebacteria from Gram-po sitive bacteria in response to antibiotic selection pressure, are prop osed, Signature sequences in proteins also indicate that the low-G+C G ram-positive bacteria are phylogenetically distinct from the high-G+C Gram-positive group and that the diderm prokaryotes (i.e. Gram-negativ e bacteria) appear to have evolved from the latter group. Protein phyl ogenies and signature sequences also show that all eukaryotic cells ha ve received significant gene contributions from both an archaebacteriu m and a Gram-negative eubacterium. Thus, the hypothesis that archaebac teria and eukaryotes shared a common ancestor exclusive of eubacteria is not supported, These observations provide evidence for an alternate view of the evolutionary relationship among living organisms that is different from the currently popular three-domain proposal.