Under nutrient limitation decline in growth rate is well described by Monod equation. (a) Final OD correlates linearly with initial substrate (NH4Cl) level: ODf(s) = a*s + b, with a = 0.066 ± 0.003 and b = 0.006 ± 0.001. This relation only saturates at high (more than 2 mM) initial nitrogen level (inset). The intersect of the linear graph is not zero probably due to low levels of nitrogen which were transferred to the media from the over-night culture together with the bacterial inoculum. (b) Growth rate as a function of substrate level, calculated using the linear relation between OD and substrate levels in (a). Line: fit to Monod law, with Ks = 2.6 ± 0.4 μM. The 0.31 mM curve deviates from the Monod fit more than other curves for unknown reasons.