English: A diagram of the mechanism of DNA uptake by Gram-negative bacteria. Bacteria that become 'naturally competent' are able to bring DNA fragments across their membranes into the cell. In this image, a DNA fragment from the environment of a naturally competent Gram-negative bacterial cell is transported across the cell's two membranes into its cytoplasm. The steps of uptake are 1. Initiation of uptake at the cell surface; 2. Uptake of the DNA across the outer membrane (o.m.); 3. Translocation of a single DNA strand across the cell's inner membrane (i.m.); 4. Recombination of the incoming strand with homologous sequences in the cell's chromosome.