Unimembranas (unimembrana) form a clade, as well as an evolutionary grade (but not a taxon), which includes all gram-positive bacteria (Posibacteria), Archaebacteria and Eukaryota. Unimembranes are characterized by the absence of an outer membrane, unlike negibacteria. Evolutionary history change the code

Unimembranes are ancestral non-photosynthetic and heterotrophic. Unimembranes would derive from a Gram-negative eurybacterium that has lost its outer membrane. This event would have happened only once in the course of evolutionary history and would therefore constitute an important apomorphic character. The only conceivable mechanism capable of causing loss of the outer membrane would be hypertrophy of the bacterial wall. This important change in the plan of organization of the bacterial cell would justify the division of this kingdom into two subregions (Negibacteria and Unibacteria). change the code

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