In situ color detection of alpha-L-arabinofuranosidase, a "no-background" reporter gene, with 5-bromo-3-indolyl-alpha-L-arabinofuranoside.

We describe the synthesis and use of 5-bromo-3-indolyl-alpha-L-arabinofuranoside (5-BI-ara) for the detection of alpha-L-arabinofuranosidase in bacterial colonies. Since the product of 5-BI-ara hydrolysis is an intensely colored indigo precipitate, it is a useful substrate for in situ detection of alpha-L-arabinofuranosidase activity. Here we show that colonies of an Escherichia coli strain expressing a recombinant alpha-L-arabinofuranosidase gene from Streptomyces lividans are readily identified by visual inspection on bacterial plates containing 5-BI-ara. Use of 5-BI-ara should facilitate the detection of endogenous alpha-L-arabinofuranosidase activity in a variety of microorganisms. In addition, since alpha-L-arabinofuranosidase activity is not commonly found in a large number of bacteria, yeast, and animal cells, 5-BI-ara will be useful in exploring the use of genes coding for alpha-L-arabinofuranosidase as gene expression reporters in heterologous systems.