Aer-2-mediated behavior in E. coli in the presence or absence of the E. coli adaptation enzymes CheR and CheB. A. Steady-state behavior of isogenic E. coli strains (CheR+ CheB+ strain UU2612, cheR cheB strain UU2610, cheR strain UU2611, and cheB strain UU2632) expressing WT Aer-2 (with 200 µM IPTG) at O2 concentrations between 20.9% and 1%. Error bars represent the standard deviation from multiple titration experiments. B. Methylation of Aer-2 in the CheR+ CheB+ strain UU2612 and the absence of methylation in the cheR cheB strain UU2610 (upper panel), at similar levels of Aer-2 accumulation (lower panel, HisProbe Western blot).