Do bacterial cryptic genes really exist?

Cryptic genes have been defined as phenotypically silent DNA sequences, usu ally not expressed during the life cycle of a microorganism, but capable of expression in a few members of a large population by mutation, recombinati on, insertion processes, or other genetic mechanisms. Recently, the cryptic ity of several genetic systems has been questioned. It appears that in many cases cryptic genes are silent only under the experimental conditions anal ysed and that their expression can be induced in the natural environment. T herefore, we propose that cryptic genes might not be a peculiar class of un iquely regulated genes, but rather genes encoding unusual functions. (C) 20 00 Editions scientifiques et medicales Elsevier SAS.