Acts as an alpha-ketoglutarate-dependent dioxygenase catalyzing hydroxylation of glutarate (GA) to L-2-hydroxyglutarate (L2HG) in the stationary phase of E.coli. Functions in a L-lysine degradation pathway that proceeds via cadaverine, glutarate and L-2-hydroxyglutarate. Other dicarboxylic acids (oxalate, malonate, succinate, adipate, and pimelate) are not substrates for this enzyme. 2-oxoglutarate + glutarate + O2 = (S)-2-hydroxyglutarate + CO2 + succinate Binds 1 Fe(2+) ion per subunit. Amino-acid degradation. Homotetramer. Expression is induced by RpoS during carbon starvation and at stationary phase. Is also regulated by cAMP-CRP and Lrp, which play the roles of a nearly essential activator and of a positive modulator, respectively. Repressed by CsiR. Makes part of the operon glaH-lhgD-gabDTP. Cells lacking this gene accumulate higher levels of glutarate than wild-type during carbon starvation and entry into the stationary phase. Belongs to the glutarate hydroxylase family. Extended N-terminus.