Probable glutamate transporter which transports extracellular glutamate into the cells. Regulates the production of intracellular reactive oxygen species (ROS) probably by controlling the synthesis of antioxidant glutathione. By regulating ROS production in blood cells, required for maintaining bacteria phagocytosis following infection with S.aureus and possibly E.coli. Expressed in the hemolymph of larvae and adults. RNAi-mediated knockdown in adult blood cells results in decreased survival following infection with S.aureus. Adults infected with S.aureus display decreased phagocytosis, increased bacterial load and increased production of reactive oxygen species (ROS) in the hemolymph. Phagocytosis of latex beads is normal, however flies pre-injected with S.aureus display a significant decrease in subsequent bead phagocytosis. Increased survival following infection with L.monocytogenes. Increased extracellular glutamate in the hemolymph. No effect on motor functions, adult weight and no increase in susceptibility to wounding. Induction of the antimicrobial peptides Drs and DptA in response to S.aureus or E.coli infection is not affected. The name 'polyphemus' derives from the Cyclops in Greek mythology that failed to guard against Odysseus as mutants are unable to defend against microbial infection. Belongs to the amino acid/polyamine transporter 2 family.