Catalyzed reporter deposition Fluorescence In Situ Hybridization (CARD-FISH) is a powerful methodology with a growing number of applications in the quantitative evaluation of microbial populations of complex ecosystems. CARD-FISH is an improvement over traditional FISH especially suitable for aquatic habitats with small, slow growing, or starving bacteria, in which the signal intensities of hybridized cells is frequently below detection limits or lost in high fluorescence background of dense mineral matrixes.
CARD is based on the tyramide signal amplification. It was introduced more than one decade ago for immunoblotting and immunosorbent assays using horseradish peroxidase (HPR) and haptenized tyramines. The basis and methodology for this technique is described in Pernthaler et al. (2002).
CARD-FISH and bioleaching
CARD-FISH is an important improvement on the fluorescence in situ hybridization technique, very useful for the detection, identification and quantification of microorganisms involved in bioleaching processes, because it can solve two important problems in the field: signal intensity and high background fluorescence of the sample. With this methodology the identification of microorganisms attached to the mineral substrate, a critical property in biohydrometallurgical processes, is rather simple, allowing its direct quantification without the need of a previous detachment.