Identical, independent, and opposing roles of ppGpp and DksA in Escherichia coli

Lisa U. Magnusson^*, Bertil Gummesson, Predrag Joksimovi, Anne Farewell, and Thomas Nyström

Department of Cell and Molecular Biology - Microbiology, Göteborg University, Box 462, 405 30 Göteborg, Sweden

^* To whom correspondence should be addressed. Email: lisa.magnusson{at}gmm.gu.se.

	Abstract

The recent discovery that the protein DksA acts as a co regulator of genes controlled by ppGpp led us to investigate the similarities and differences between the relaxed phenotype of a ppGpp deficient mutant and the phenotype of a strain lacking DksA. We demonstrate that the absence of DksA and ppGpp have similar effects on many of the observed phenotypes but that DksA and ppGpp also have independent and sometimes opposing roles in the cell. Specifically, we show that overexpression of DksA can compensate for the loss of ppGpp with respect to PuspA, PlivJ and PrrnBP1 transcription as well as amino acid auxotrophy, cell-cell aggregation, motility, filamentation and stationary phase morphology suggesting that DksA can function without ppGpp in regulating gene expression. In addition, ppGpp and DksA have opposing effects on adhesion. In the course of our analysis, we also discovered new features of the relaxed mutant, namely defects in cell-cell aggregation and motility.