A Spectrofluorophotometrical Method Based on Fura-2-AM Probe to Determine Cytosolic Ca²⁺ Level in Pseudomonas syringae Complex Bacterial Cells

Calcium signaling is an emerging mechanism by which bacteria respond to environmental cues. To measure the intracellular free-calcium concentration in bacterial cells, [Ca²⁺]_i, a simple spectrofluorometric method based on the chemical probe Fura 2-acetoxy methyl ester (Fura 2-AM) is here presented using Pseudomonad bacterial cells. This is an alternative and quantitative method that can be completed in a short period of time with low costs, and it does not require the induction of heterologously expressed protein-based probes like Aequorin. Furthermore, it is possible to verify the properties of membrane channels involved in Ca²⁺ entry from the extracellular matrix. This method is in particular valuable for measuring [Ca²⁺]_i in the range of 0.1-39.8 µM in small cells like those of prokaryotes.