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Early termination of the Shiga toxin transcript generates a regulatory small RNA

ABSTRACT: Enterohaemorrhagic E. coli is significant human pathogen that causes disease ranging from haemorrhagic colitis to haemolytic uremic syndrome. The later can lead to potentially fatal renal failure and is caused by the release of Shiga toxins that are encoded within lambdoid bacteriophages. The toxins are encoded within the late transcript of the phage and are regulated by anti-termination of the PR’ late promoter during lytic induction of the phage. During lysogeny, the late transcript is prematurely terminated at tR’ immediately downstream of PR’, generating a short RNA that is a by-product of anti-termination regulation. We demonstrate that this short transcript binds the small RNA chaperone Hfq, and is processed into a stable 74 nt regulatory small RNA that we have termed, StxS. StxS activates expression of the general stress response sigma factor, RpoS, through direct interactions with an activating seed sequence within the 5’ UTR. StxS represses expression of Shiga toxin 1 and activation of RpoS promotes high cell density growth under nutrient limiting conditions. Many phages utilise anti-termination to regulate the lytic/lysogenic switch and our results demonstrate that short RNAs generated as a by-product of this regulation can acquire regulatory small RNA features and modulate host fitness.

ORGANISM(S): Escherichia coli O157:H7 str. Sakai

PROVIDER: GSE143631 | GEO | 2020/09/16

REPOSITORIES: GEO

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Project description:The alternative sigma factor RpoS plays a central role in the critical host-adaptive response of the Lyme disease spirochete, Borrelia burgdorferi. We previously identified bbd18 as a negative regulator of RpoS but could not inactivate bbd18 in wild-type spirochetes. In the current study we employed an inducible bbd18 gene to demonstrate the essential nature of BBD18 for viability of wild-type spirochete viability in vitro and at a unique point in vivo. Transcriptomic analyses of BBD18 depleted cells demonstrated global induction of RpoS-dependent genes prior to lysis, with the absolute requirement for BBD18, both in vitro and in vivo, circumvented by deletion of rpoS. The increased expression of plasmid prophage genes and the presence of phage particles in the supernatants of lysing cultures indicate that RpoS regulates phage lysis-lysogeny decisions. Through this work we identify a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete. The alternative sigma factor RpoS plays a central role in the critical host-adaptive response of the Lyme disease spirochete, Borrelia burgdorferi. We previously identified bbd18 as a negative regulator of RpoS but could not inactivate bbd18 in wild-type spirochetes. In the current study we employed an inducible bbd18 gene to demonstrate the essential nature of BBD18 for viability of wild-type spirochete viability in vitro and at a unique point in vivo. Transcriptomic analyses of BBD18 depleted cells demonstrated global induction of RpoS-dependent genes prior to lysis, with the absolute requirement for BBD18, both in vitro and in vivo, circumvented by deletion of rpoS. The increased expression of plasmid prophage genes and the presence of phage particles in the supernatants of lysing cultures indicate that RpoS regulates phage lysis-lysogeny decisions. Through this work we identify a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete.

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Early termination of the Shiga toxin transcript generates a regulatory small RNA

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