NEW EMBO MEMBERS' REVIEW: The black cat/white cat principle of signal integration in bacterial promoters

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Abstract
‘Black cat, white cat: whatever catches the mouse is a good cat’ (Chinese proverb). Throughout the 3000 million years that bacteria have been on planet Earth, they have evolved amazing mechanisms for rapid adaptation to every imaginable type of environmental change. To give one extreme example, as little as 50 years after the introduction of the first antibiotics, very few of these drugs remain effective today at combating microbial infections (Davies, 1997). When bacteria are faced with antimicrobials, the only challenge they must overcome is to defeat the toxic effect of the compound through modification, cleavage or pumping the drug out of the cells; these processes generally involve one or just a few proteins. A far more complex environmental threat is that posed by organic chemicals, which have been discharged into many ecosystems through industrial and urban activities. Many of these chemicals are xenobiotic compounds (literally, alien to life), which include types of chemical ligatures (typically covalent C–Cl bonds) that have never been present in significant amounts in the biosphere and against which the housekeeping metabolic pathways of most microbes are generally useless (van der Meer et al ., 1992). Unlike antibiotics, the challenge in this case is the construction of entire biodegradation pathways that endow bacteria with the ability to grow on these otherwise unpalatable chemicals. Such an outcome involves not just one protein, but sometimes dozens, which must adapt to entirely new substrates and intermediates. However, difficult as this might be, the successful assembly of a degradation pathway does not guarantee per se the survival of a particular strain. Bacteria that colonize polluted sites are subject to extremely tough competition from other microbial residents of the same niche. Transcriptional regulation of biodegradative genes and operons thus becomes a critical asset for the success of a newly assembled pathway to …

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