Fig. 2.

Aerotaxis phenotypes of Aer mutants in Tryptone and succinate semi-solid agar. A. Aer mutant proteins were expressed in the receptorless strain, BT3388 (aer tsr tar tap trg), and colonies were inoculated into Tryptone semi-solid agar containing 50 µg ml⁻¹ ampicillin and IPTG ranging from 20 to 1000 µM. Plates were incubated at 30°C for 16 h and the colony morphologies were compared with positive (wild-type Aer) and negative (vector) aerotaxis controls. Examples shown are for plasmids pKW1 (wild-type Aer), pKW1-G76E (leaky), pKW1-Y93C (null) and pTrc99A (vector).

B. Plasmids isolated from aerotaxis-defective colonies in (A) were introduced into BT3312 (aer tsr) to test for functional rescue by Tar. Colonies were inoculated into succinate semi-solid agar containing 50 µg ml⁻¹ ampicillin and IPTG ranging from 0 to 1000 µM, and plates were incubated at 30°C for 18 to 19 h. Examples shown are for plasmids pKW1 (wild-type Aer), pKW1-S80I (rescued) and pKW1-Y93C (non-rescued), and pTrc99A (vector).