Transposition is modulated by a diverse set of host factors in Escherichia coli and is stimulated by nutritional stress.

The role of host factors in regulating bacterial transposition has never been comprehensively addressed, despite the potential consequences of transposition. Here, we describe a screen for host factors that influence transposition of IS903, and the effect of these mutations on two additional transposons, Tn10 and Tn552. Over 20,000 independent insertion mutants were screened in two strains of Escherichia coli; from these we isolated over 100 mutants that altered IS903 transposition. These included mutations that increased or decreased the extent of transposition and also altered the timing of transposition during colony growth. The large number of gene products affecting transposition, and their diverse functions, indicate that the overall process of transposition is modulated at many different steps and by a range of processes. Previous work has suggested that transposition is triggered by cellular stress. We describe two independent mutations that are in a gene required for fermentative metabolism during anaerobic growth, and that cause transposition to occur earlier than normal during colony development. The ability to suppress this phenotype by the addition of fumarate therefore provides direct evidence that transposition occurs in response to nutritional stress. Other mutations that altered transposition disrupted genes normally associated with DNA metabolism, intermediary metabolism, transport, cellular redox, protein folding and proteolysis and together these define a network of host proteins that could potentially allow readout of the cell's environmental and nutritional status. In summary, this work identifies a collection of proteins that allow the host to modulate transposition in response to cell stress.

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