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[130] [129] In bacteria and archaea, action potential-like phenomena have been observed in biofilms [131] and also single cells such as cable bacteria. [129] The archaeon Halobacterium salinarium shows a photophobic response characterized by a 180° reversal of its swimming direction induced by a reversal in the direction of flagellar rotation.
Bacteria within the Deinococcota group may also exhibit Gram-positive staining but contain some cell wall structures typical of Gram-negative bacteria. The cell wall of some Gram-positive bacteria can be completely dissolved by lysozymes which attack the bonds between N-acetylmuramic acid and N-acetylglucosamine.
Spiral bacteria are another major bacterial cell morphology. [2] [30] [31] [32] Spiral bacteria can be sub-classified as spirilla, spirochetes, or vibrios based on the number of twists per cell, cell thickness, cell flexibility, and motility. [33] Bacteria are known to evolve specific traits to survive in their ideal environment. [34]
Twitching motility is a form of crawling bacterial motility used to move over surfaces. Twitching is mediated by the activity of hair-like filaments called type IV pili which extend from the cell's exterior, bind to surrounding solid substrates, and retract, pulling the cell forwards in a manner similar to the action of a grappling hook.
Some bacteria transfer genetic material between cells. This can occur in three main ways. First, bacteria can take up exogenous DNA from their environment in a process called transformation. [138] Many bacteria can naturally take up DNA from the environment, while others must be chemically altered in order to induce them to take up DNA. [139]
The general secretion (Sec) involves secretion of unfolded proteins that first remain inside the cells. In Gram-negative bacteria, the secreted protein is sent to either the inner membrane or the periplasm. But in Gram-positive bacteria, the protein can stay in the cell or is mostly transported out of the bacteria using other secretion systems.
Bacteria in Cytophagales are all Gram-negative and non-spore forming. [10] [4] [11] They are non-flagellated, but move by exhibiting a gliding or flexing motion. Cytophagales are all unicellular, with rod-shaped cells that can differ significantly in shape. [10] Cells can be short or long, delicate or stout, and have tapering or rounded ends.
Gram staining differentiates bacteria by the chemical and physical properties of their cell walls. Gram-positive cells have a thick layer of peptidoglycan in the cell wall that retains the primary stain, crystal violet. Gram-negative cells have a thinner peptidoglycan layer that allows the crystal violet to wash out on addition of ethanol.