Ammonium/proton antiporter that mediates the efflux of ammonium ions. Can also transport potassium or rubidium, but not sodium or lithium. AmhT alone exhibits antiport activity, but interaction with AmhM confers different properties, such as higher KM for potassium. Interacts with AmhM. Deletion affects endospore formation and germination. Belongs to the monovalent cation:proton antiporter 2 (CPA2) transporter (TC 2.A.37) family.