No abstract

Cells of Escherichia coli elicit stringent control of ribosome production during the transition from exponential growth to stationary phase (Sands and Roberts 1952;Stent and Brenner 1961). The effector molecule of the stringent control modulon is the alarmone guanosine tetraphosphate, ppGpp (Cashel and Gallant 1969;Lazzarini et al. 1971; Ryals et al. 1982a,b,c;Baracchini and Bremer 1988). The production of this nucleotide is dependent on the (p)ppGpp synthetases PSI and PSII encoded by the relA and spoT genes, respectively (Xiao et al. 1991). The alarmone ppGpp binds to the ␤ and ␤Ј subunits of core RNA polymerase (E) (Chatterji et al. 1998;Toulokhonov et al. 2001) and thereby inhibits superfluous rRNA biosynthesis during growth inhibition (e.g., Travers 1976;Gourse et al. 1986;Ohlsen and Gralla 1992;Heinemann and Wagner 1997;Zhou and Jin 1998 , such promoters may be argued to be especially sensitive to the destabilizing effects of ppGpp . Consistent with this idea, it has been shown that RNA polymerase (RNAP) mutants that suppress the requirement for ppGpp in vivo form unstable complexes with stable RNA promoters in vitro (Zhou and Jin 1998).The alarmone ppGpp can also act as a positive effector of gene expression, and some 70 -dependent genes require this nucleotide for their induction during growth arrest (Xiao et al. 1991;Nyström 1994;Kvint et al. 2000b). In addition, many operons encoding amino acid biosynthetic pathways require ppGpp for their transcription, and E. coli cells lacking ppGpp are polyauxotrophs (Xiao et al. 1991). It has been suggested that the effect of ppGpp on such promoters is linked to ppGpp-dependent changes in core availability. According to a model by Zhou and Jin (1998), the rate-limiting step of promoters that are positively regulated by ppGpp is E 70 recruitment, and it is argued that these promoters would therefore be very sensitive to the concentration of free RNA polymerase. Thus, the accumulation of ppGpp is suggested to result in the dissociation of core from stringent rrnP1 promoters and the consequent increased availability of core leads to elevated initiation of transcription at promoters that have a relatively poor ability to recruit E 70 (Zhou and Jin 1998). Some aspects of this model have been supported recently by in vivo and in vitro transcription assays (Barker et al. 2001a,b).To add to the role of ppGpp in the cell, genes requiring

Summary

There is growing understanding that the environment plays an important role both in the transmission of antibiotic resistant pathogens and in their evolution. Accordingly, researchers and stakeholders world-wide seek to further explore the mechanisms and drivers involved, quantify risks and identify suitable interventions. There is a clear value in establishing research needs and coordinating efforts within and across nations in order to best tackle this global challenge. At an international workshop in late September 2017, scientists from 14 countries with expertise on the environmental dimensions of antibiotic resistance gathered to define critical knowledge gaps. Four key areas were identified where research is urgently needed: 1) the relative contributions of different sources of antibiotics and antibiotic resistant bacteria into the environment; 2) the role of the environment, and particularly anthropogenic inputs, in the evolution of resistance; 3) the overall human and animal health impacts caused by exposure to environmental resistant bacteria; and 4) the efficacy and feasibility of different technological, social, economic and behavioral interventions to mitigate environmental antibiotic resistance..

RpoS-dependent promoters require ppGpp for induction in the stationary phase. This has been thought to be a simple consequence of S itself requiring ppGpp for its production. By using four model promoters requiring S for normal induction in the stationary phase, we demonstrate that S -dependent promoters require ppGpp even in the presence of high levels of S produced ectopically. Similar to 70 -dependent promoters under positive control by ppGpp, the requirement of S -dependent promoters for this alarmone is bypassed by specific "stringent" mutations in the ␤-subunit of RNA polymerase. The results suggest that stationary phase induction of both S -and 70 -dependent genes requires the stringent control modulon and that stringency confers dual control on the RpoS regulon by affecting promoter activity and the levels of the required -factor.