Magnetotactic bacteria (or MTB) are a polyphyletic group of bacteria discovered by Richard P. Blakemore in 1975, that orient along the magnetic field lines of Earth's magnetic field. To perform this task, these bacteria have organelles called magnetosomes that contain magnetic crystals. The biological phenomenon of microorganisms tending to move in response to the environment's magnetic characteristics is known as magnetotaxis (although this term is misleading in that every other application of the term taxis involves a stimulus-response mechanism). In contrast to the magnetoception of animals, the bacteria contain fixed magnets that force the bacteria into alignment — even dead cells align, just like a compass needle. The alignment is believed to aid these organisms in reaching regions of optimal oxygen concentration.