Mediates bacteriorhodopsin- and halorhodopsin-dependent photoresponses by detecting membrane potential changes. Probably transduces the signal to the histidine kinase CheA. Interacts with CheA, CheY and CheW1. Methylated by CheR. Deletion abolishes bacteriorhodopsin- and halorhodopsin-dependent phototaxis. Belongs to the methyl-accepting chemotaxis (MCP) protein family.