Changes of DNA topology affect the global transcription landscape and allow rapid growth of a Bacillus subtilis mutant lacking carbon catabolite repression

Bacteria are able to prioritize preferred carbon sources from complex mixtures. This is achieved by the regulatory phenomenon of carbon catabolite repression. To allow the simultaneous utilization of multiple carbon sources and to prevent the time-consuming adaptation to each individual nutrient in biotechnological applications, mutants lacking carbon catabolite repression can be used. However, such mutants often exhibit pleiotropic growth defects. We have isolated and characterized mutations that overcome the growth defect of Bacillus subtilis ccpA mutants lacking the major regulator of catabolite repression, in particular their glutamate auxotrophy. Here we show, that distinct mutations affecting the essential DNA topoisomerase I (TopA) cause glutamate prototrophy of the ccpA mutant. These suppressing variants of the TopA enzyme exhibit increased activity resulting in enhanced relaxation of the DNA. Reduced DNA supercoiling results in enhanced expression of the gltAB operon encoding the biosynthetic glutamate synthase. This is achieved by a significant re-organization of the global transcription network accompanied by re-routing of metabolism, which results in inactivation of the glutamate dehydrogenase. Our results provide a link between DNA topology, the global transcriptional network, and glutamate metabolism and suggest that specific topA mutants may be well suited for biotechnological purposes.