To test for the functional effects of BcsQ and BcsR point mutants or truncated variants, we resorted to a functional complementation assay as established previously (4 (link)). First, chemically competent cells were prepared from E. coli 1094 ΔbcsQ or ΔbcsR deletion strains (4 (link)). These were then transformed with low-copy pAM-238 plasmids carrying wild-type or mutant bcsQ or bcsR genes and plated on LB-agar plates (Miller) supplemented with the appropriate antibiotics [streptomycin (60 μg/ml) and chloramphenicol (15 μg/ml)]. Single colonies were inoculated in 5 ml of LB medium with antibiotics and left to grow overnight at 37°C and agitation. On the following morning, 5 μl of the cultures was spotted onto low-salt LB-agar plates [NaCl (1.5 g/liter)] supplemented with the antibiotics, 0.1 mM IPTG, and 0.02% calcofluor (Fluorescent Brightener 28, Sigma-Aldrich). The spots were allowed to air-dry, and the plates were incubated at 30°C. After 24 hours, the plates were photographed under brief illumination with long-wave ultraviolet light (365 nm).