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

Abstract

SummaryThe 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 IS 903 , and the effect of these mutations on two additional transposons, Tn 10 and Tn 552 . Over 20 000 independent insertion mutants were screened in two strains of Escherichia coli ; from these we isolated over 100 mutants that altered IS 903 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.

Evidence that the insertion events of IS2 transposition are biased towards abrupt compositional shifts in target DNA and modulated by a diverse set of culture parameters

“…Published examples of these are the detection of IS1 and IS5 in an HIV DNA vaccine (Prather et al 2006), the contamination with IS1 of a plasmid used for cystic fibrosis therapy (Boyd et al 1999), and the detection of IS2 transposition upstream of the neo R gene of the mammalian expression vector and DNA vaccine backbone pCIneo (Oliveira et al 2009b). Interestingly, van der Heijden and coworkers recently observed an IS2 transposition event in a plasmid from the pVAX1 family (van der Heijden et al 2013). In this case, the insert could be detected between the BGH polyadenylation signal and the neo R gene during a fed-batch fermentation step, but not in the inoculum from the master cell bank.…”

“…The latter is usually greatly suppressed under optimal growth conditions, but transiently or permanently activated in response to situations of cellular stress (Eichenbaum and Livneh 1998;Twiss et al 2005). This so-called stressinduced transposition allows for fast genetic changes to take place, fuelling the emergence of novel and advantageous traits able to overcome stress.…”

Engineering of bacterial strains and vectors for the production of plasmid DNA

“…Prolonged cultivation in minimal medium may have caused the high incidence of IS insertion detected in this study, as transposon activity can often be induced by environmental stressors such as nutrient limitation (Twiss et al 2005). The population of low-producers was detrimental to process efficiency by necessitating extensive screening for high-producing clones for use in master seed banks.…”

Extremely low frequency magnetic field exposure affects DnaK and GroEL expression in E. coli cells with impaired heat shock response

“…At the level of transcription initiation, the recognition of heat shock promoters is mediated by the alternative sigma factor σ 32 that is tightly controlled mainly at the translational and posttranslational levels, where controlled proteolysis play a crucial role (Guisbert et al 2004). It is well known that proteases are involved in remodeling the bacterial proteome in response to changes in cellular environment; since they play a role both in HSR and in transposition regulation (Twiss et al 2005) they could be involved in the observed phenomena.…”