The flagellar motor has a default direction of rotation, counterclockwise

The flagellar motor has a default direction of rotation, counterclockwise 

The chemotaxis protein CheY was subsequently identified by both the whole-cell and reductionist approaches as the clockwise signal, i.e., as the molecule that interacts with the switch, thereby promoting clockwise rotation. In the whole-cell approach, second-site suppression analysis implied that CheY interacts with the switch (for reviews, see [56, 459]), and overproduction of CheY in a gutted strain generated clockwise rotation ([168] for a review, see reference [212]). In the reductionist approach, purified CheY inserted into cytoplasm-free envelopes caused some of the envelopes to rotate clockwise [594]. The absence of cytoplasmic chemotaxis proteins in the intact cells and the absence of cytoplasm in the envelopes indicated that the interaction of CheY with the switch is direct. Later biochemical studies demonstrated 

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