Affect of sodium concentration on solute uptake. Uptake of 5 μM (0.125 μCi) l-[U-14C]lactate or 25 μM (0.125 μCi) [2,3-14C]succinate or 25 μM (0.125 μCi) l-[U-14C]glutamic acid was assayed by the rapid filtration method for R. leguminosarum strains 3841, RU1632 (RU1357 pRU976),or RU1633 (RU1357 pRU986) grown in minimal medium (AMS) with added succinate (10 mM) plus ammonium chloride (10 mM). Uptake assays were performed in sodium-free RMS with no additions (black columns), with added NaCl (5 mM) (white columns), or with added LiCl (5 mM) (grey columns). Data shown are the means of at least three independent experiments. nd, not determined.