Two different magneto-aerotactic mechanisms—known as polar and axial—are found in different MTB strains.[25] Some strains that swim persistently in one direction along the magnetic field (either north-seeking [NS] or south-seeking [SS])—mainly the magnetotactic cocci—are polar magneto-aerotactic. These magnetotactic bacteria will travel along the lines of the earth's magnetic field according to their orientation, but will swerve as a group and reverse direction if exposed to a local, more powerful and oppositely-oriented magnetic field. In this way, they continue to travel in the same magnetic direction, but relative instead to the local field.