Proton symporter that senses osmotic shifts and responds by importing osmolytes such as proline, glycine betaine, stachydrine, pipecolic acid, ectoine and taurine. It is both an osmosensor and an osmoregulator which is available to participate early in the bacterial osmoregulatory response. Induced by an increase in the osmolarity of the growth medium. Belongs to the major facilitator superfamily. Metabolite:H+ Symporter (MHS) family (TC 2.A.1.6) family.