Fig 4. Imaging bacterial colonies expressing a FRET biosensor library.

(A) Basal ratio R₀ plotted against calcium-induced ratio change ΔR/R for every colony of one agar plate blotted onto white paper. Each colony is supposed to express a different diversified FRET calcium sensor variant. The 10 best performing colonies of this experiment are highlighted in yellow and numbered. (B) Single FRET traces of the 10 best colonies as identified in A. The arrow indicates when calcium was applied (C) Scheme of a screening plate with the positions of the 10 best performing colonies highlighted.