Mechanistic model of nutrient uptake explains dichotomy between marine oligotrophic and copiotrophic bacteria
Fig 6
The effective half-saturation concentration of ABC transport.
ABC transport systems achieve low optimal half-saturation concentrations (Keff, magenta curve and axis)—and thus high specific affinities—as nutrient concentrations decrease by maintaining a high surface-area-to-volume ratio and increasing the ratio of the abundance of binding proteins to the abundance of membrane-bound transport units (turquoise curve and axis). For high binding protein to transport unit ratios, the Michaelis-Menten approximation of ABC transport (Eq 6) holds (S1 Fig). At 1 nM, where the binding protein to transport unit ratio is approximately seven, the approximation gives Keff ≈ 1.5 nM, while the calculated Keff = 2.9 nM. (For a plot showing how we calculate the effective half-saturation concentration, see S7 Fig).