Transmembrane receptors in the signaling pathways of bacterial chemotaxis systems influence cell motility by forming noncovalent complexes with the cytoplasmic signaling proteins to regulate their activity. The casing may include a plurality of panel elements joined to each other with welds, and portions of the panel elements that include the welds may project toward an interior of the ball. A cam system operates upon rotation of the cylinders to elevate the caps into sealing relationship with the printhead nozzle plates.