Gram-Positive Bacteria

Definition

A Gram-positive bacterium is a prokaryotic cell whose cell wall consists of mainly peptidoglycan and lacks the outer membrane characteristic of the Gram-negative cells. Bacteria can be divided into two major groups, called Gram positive and Gram negative. The original distinction between both groups was based on the Gram stain, which depends on differences in the structure of the cell wall (see Cell Wall). The Gram-negative cell wall is a mutilayered structure and quite complex, whereas the Gram-positive cell wall consists of a single type of molecule, the peptidoglycan, which is often much thicker. In Gram-positive bacteria, as much as 90 % of the cell wall consists of peptidoglycan, although another molecule, teichoic acid, is usually present in small amounts. The phylogenetic analysis of bacteria has demonstrated that the cell wall structure is phylogenetically consistent: all Gram-positive bacteria form a coherent phylogenetic group. The Gram-positive bacteria are a...