Date Published: July 10, 2014
Publisher: Public Library of Science
Author(s): Nicolas Papon, Vincent Courdavault, Arnaud Lanoue, Marc Clastre, Matthias Brock, William E. Goldman.
BLI is a powerful biophotonic imaging technology that allows in vivo visualization of temporal and spatial progression of infections in living organisms. BLI relies on the detection of visible light arising from an enzymatic reaction of oxidation known as bioluminescence. Originally, bioluminescence referred to the light emission of living organisms (e.g., bacteria, fungi, fish, insects, algae, and squid), which results from the oxidation of organic substrates mediated by catalysts named luciferases (Figure 1A) . This fascinating natural phenomenon has been thus diverted to create bioluminescent microorganisms that are currently used in BLI as bioreporters. BLI has the advantages of being highly sensitive with excellent signal-to-noise ratios, and being non-invasive and nontoxic for animals. Such an approach has been applied in the past two decades to study the fate of tumor cells in various therapeutic settings and of several infectious agents including bacteria, viruses, parasitic protozoa, and, more recently, opportunistic fungi .
The development of BLI strategies for monitoring infections requires the construction of luciferase-expressing microorganisms that fit the special needs of subsequent experiments. To date, three different luciferase genes have been applied to infection studies on yeast and mold: (i) the firefly (Photinus pyralis) fLUC gene encoding a luciferase (Fluc), which converts the substrate luciferin to oxy-luciferin in an ATP-dependent manner, and (ii) the sea pansy (Renilla reniformis) rLUC and (iii) the copepod Gaussia (Gaussia princeps) gLUC, which both encode coelenterazine dependent luciferases (Rluc and Gluc, respectively) (Figure 1A) .
During the last decade, many efforts have been made to develop pioneering models of BLI for the most common opportunistic fungal infections such as candidiasis and aspergillosis.
The primary vocation of BLI for pathogenic fungal agents is to offer the possibility to follow with extreme accuracy, in real-time and in a non-invasive manner, the proliferation of microorganisms within intact living animals (Figure 1B).
Although recent advances clearly demonstrate the potential of BLI for monitoring cutaneous, subcutaneous, mucosal, and invasive mycosis, the available systems still suffer from major limitations, which have to be overcome to further expand their field of use.