Stress and regulation of sex in bacteria (STARS)

Conjugative DNA transfer plays a key role in the spread of antibiotic resistance genes and is regulated by plasmid encoded and host encoded factors. Based on experimental evidence we suggest that the expression of transfer genes and the assembly of the DNA transfer apparatus represent a form of stress for the bacterium which is sensed by the Cpx two-component system and/or by ECF (extracytoplasmic function) sigma factors. In our working model the signals sensed by these two systems elicit a cellular stress response very similar to the "classical" heat shock response. Our preliminary data support this model, furthermore, transcription of tra genes of the F-like plasmid R1- 16 was deregulated in a groEL ts mutant at the non-permissive temperature and resulted in lysis of cells. The aim of the proposed research effort is to investigate how this stress response is induced and which host proteins are involved in regulation of tra gene expression. To solve these questions we will mainly focus on a whole genome approach and expression profiles (mRNA levels, protein levels and synthesis rates) of wild type and mutant E. coli strains with and without a conjugative plasmid. Detailed single gene analyses will be performed to corroborate the data obtained in the genomic approach. Results from our studies will provide new insights into regulation of conjugative DNA transfer and how the interplay between conjugative plasmids and their hosts is designed to provide maximum efficiency of DNA transfer with minimum metabolic burden for the bacterium. The expected results of the research effort will enable us to design new strategies to combat the re-emerging threat caused by the spread of antibiotic resistance genes and will eventually allow to define new targets to develop anti-infective drugs.

In our research project "Stress and Regulation of Sex in Bacteria" we focused on the issue whether bacteria harbouring a special secretion machinery, termed the type IV secretion system, specifically react to the expression and assembly of this machinery. Type IV secretion systems represent important "weapons" for pathogenic bacteria. Through type IV secretion machineries substrate molecules such as DNA and proteins are transported to other cells where they elicit certain responses. Through the action of type IV secretion systems antibiotic resistance genes can spread within populations of pathogenic bacteria, virulence factors and toxins can be secreted, and in plants, tumor growth can be induced. Since the assembly of the type IV secretion machinery takes place in the cell envelope we investigated whether this was sensed by extracellular and cellular stress sensing systems. Genetic networks that respond to stress situations allow bacteria to rapidly adapt to critical situations such as elevated temperatures and nutrient limitations. For reprogramming bacteria are endowed with special transcription factors - sigma factors - that control large sets of genes and with two-component systems that respond to signals in the cell or from the environment. The most important result from our research efforts can be summarized in one sentence: "Sex is Stress", meaning that bacteria indeed react to the expression and assembly of a functional type IV secretion system. Bacteria that transmit their genes into other bacteria via a type IV secretion machinery activate a two-component regulatory system and a sigma factor which acts as a global regulator. For bacterial cells this activation has a protective role and it also leads to a negative feed-back on the expression of the type IV secretion genes. We could also show that stress (in our case heat-shock) prevents the activation of the type IV secretion system - "Stress prevents Sex". This finding is important since it opens the way to new strategies for combating the spread of antibiotic resistance genes and for the development of novel anti-infective treatments.