Figure 3. P. mirabilis encodes multiple transporters that contribute to both serine and threonine import.

Wild-type P. mirabilis and indicated serine/threonine import mutants were cultured in standard PMSM or formulations containing either l-serine or l-threonine as the sole carbon or nitrogen source. (A) Growth of wild-type P. mirabilis, serine/threonine import single mutants, and ΔsstTΔsdaC double mutant in standard PMSM. (B) Growth of wild-type P. mirabilis, serine/threonine import single mutants, and ΔsstTΔsdaC double mutant in PMSM containing l-serine as the sole nitrogen source. The ΔsdaABΔdsdA mutant was included as a no-growth control. (C) Growth of wild-type P. mirabilis was compared across standard PMSM and PMSM containing l-threonine as the sole carbon or nitrogen source. (D) Growth of wild-type P. mirabilis, serine/threonine import single mutants, and ΔsstTΔsdaC double mutant in PMSM containing l-threonine as the sole nitrogen source. All cultures were incubated at 37°C with aeration in 96-well plates, and growth was assessed by measurement of OD₆₀₀ at 15-minute intervals for 18 hours. Error bars represent mean ± SD from at least 6 technical replicates, and graphs are representative of at least 3 independent experiments.