A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner

ABSTRACT Legionella pneumophila is an environmental bacterium that parasitizes protozoa, but it may also infect humans, thereby causing a severe pneumonia called Legionnaires’ disease. To cycle between the environment and a eukaryotic host, L. pneumophila is regulating the expression of virulence fa...

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Autores principales:	Giulia Oliva, Tobias Sahr, Monica Rolando, Maike Knoth, Carmen Buchrieser
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2017
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/c7950b9fecdd4facb8c8391ea8332abb
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spelling	oai:doaj.org-article:c7950b9fecdd4facb8c8391ea8332abb2021-11-15T15:51:06ZA Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner10.1128/mBio.02182-162150-7511https://doaj.org/article/c7950b9fecdd4facb8c8391ea8332abb2017-03-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.02182-16https://doaj.org/toc/2150-7511ABSTRACT Legionella pneumophila is an environmental bacterium that parasitizes protozoa, but it may also infect humans, thereby causing a severe pneumonia called Legionnaires’ disease. To cycle between the environment and a eukaryotic host, L. pneumophila is regulating the expression of virulence factors in a life cycle-dependent manner: replicating bacteria do not express virulence factors, whereas transmissive bacteria are highly motile and infective. Here we show that Hfq is an important regulator in this network. Hfq is highly expressed in transmissive bacteria but is expressed at very low levels in replicating bacteria. A L. pneumophila hfq deletion mutant exhibits reduced abilities to infect and multiply in Acanthamoeba castellanii at environmental temperatures. The life cycle-dependent regulation of Hfq expression depends on a unique cis-encoded small RNA named Anti-hfq that is transcribed antisense of the hfq transcript and overlaps its 5′ untranslated region. The Anti-hfq sRNA is highly expressed only in replicating L. pneumophila where it regulates hfq expression through binding to the complementary regions of the hfq transcripts. This results in reduced Hfq protein levels in exponentially growing cells. Both the small noncoding RNA (sRNA) and hfq mRNA are bound and stabilized by the Hfq protein, likely leading to the cleavage of the RNA duplex by the endoribonuclease RNase III. In contrast, after the switch to transmissive bacteria, the sRNA is not expressed, allowing now an efficient expression of the hfq gene and consequently Hfq. Our results place Hfq and its newly identified sRNA anti-hfq in the center of the regulatory network governing L. pneumophila differentiation from nonvirulent to virulent bacteria. IMPORTANCE The abilities of L. pneumophila to replicate intracellularly and to cause disease depend on its capacity to adapt to different extra- and intracellular environmental conditions. Therefore, a timely and fine-tuned expression of virulence factors and adaptation traits is crucial. Yet, the regulatory circuits governing the life cycle of L. pneumophila from replicating to virulent bacteria are only partly uncovered. Here we show that the life cycle-dependent regulation of the RNA chaperone Hfq relies on a small regulatory RNA encoded antisense to the hfq-encoding gene through a base pairing mechanism. Furthermore, Hfq regulates its own expression in an autoregulatory loop. The discovery of this RNA regulatory mechanism in L. pneumophila is an important step forward in the understanding of how the switch from inoffensive, replicating to highly virulent, transmissive L. pneumophila is regulated.Giulia OlivaTobias SahrMonica RolandoMaike KnothCarmen BuchrieserAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 8, Iss 1 (2017)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Giulia Oliva Tobias Sahr Monica Rolando Maike Knoth Carmen Buchrieser A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner
description	ABSTRACT Legionella pneumophila is an environmental bacterium that parasitizes protozoa, but it may also infect humans, thereby causing a severe pneumonia called Legionnaires’ disease. To cycle between the environment and a eukaryotic host, L. pneumophila is regulating the expression of virulence factors in a life cycle-dependent manner: replicating bacteria do not express virulence factors, whereas transmissive bacteria are highly motile and infective. Here we show that Hfq is an important regulator in this network. Hfq is highly expressed in transmissive bacteria but is expressed at very low levels in replicating bacteria. A L. pneumophila hfq deletion mutant exhibits reduced abilities to infect and multiply in Acanthamoeba castellanii at environmental temperatures. The life cycle-dependent regulation of Hfq expression depends on a unique cis-encoded small RNA named Anti-hfq that is transcribed antisense of the hfq transcript and overlaps its 5′ untranslated region. The Anti-hfq sRNA is highly expressed only in replicating L. pneumophila where it regulates hfq expression through binding to the complementary regions of the hfq transcripts. This results in reduced Hfq protein levels in exponentially growing cells. Both the small noncoding RNA (sRNA) and hfq mRNA are bound and stabilized by the Hfq protein, likely leading to the cleavage of the RNA duplex by the endoribonuclease RNase III. In contrast, after the switch to transmissive bacteria, the sRNA is not expressed, allowing now an efficient expression of the hfq gene and consequently Hfq. Our results place Hfq and its newly identified sRNA anti-hfq in the center of the regulatory network governing L. pneumophila differentiation from nonvirulent to virulent bacteria. IMPORTANCE The abilities of L. pneumophila to replicate intracellularly and to cause disease depend on its capacity to adapt to different extra- and intracellular environmental conditions. Therefore, a timely and fine-tuned expression of virulence factors and adaptation traits is crucial. Yet, the regulatory circuits governing the life cycle of L. pneumophila from replicating to virulent bacteria are only partly uncovered. Here we show that the life cycle-dependent regulation of the RNA chaperone Hfq relies on a small regulatory RNA encoded antisense to the hfq-encoding gene through a base pairing mechanism. Furthermore, Hfq regulates its own expression in an autoregulatory loop. The discovery of this RNA regulatory mechanism in L. pneumophila is an important step forward in the understanding of how the switch from inoffensive, replicating to highly virulent, transmissive L. pneumophila is regulated.
format	article
author	Giulia Oliva Tobias Sahr Monica Rolando Maike Knoth Carmen Buchrieser
author_facet	Giulia Oliva Tobias Sahr Monica Rolando Maike Knoth Carmen Buchrieser
author_sort	Giulia Oliva
title	A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner
title_short	A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner
title_full	A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner
title_fullStr	A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner
title_full_unstemmed	A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner
title_sort	unique <italic toggle="yes">cis</italic>-encoded small noncoding rna is regulating <italic toggle="yes">legionella pneumophila</italic> hfq expression in a life cycle-dependent manner
publisher	American Society for Microbiology
publishDate	2017
url	https://doaj.org/article/c7950b9fecdd4facb8c8391ea8332abb
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A Unique <italic toggle="yes">cis</italic>-Encoded Small Noncoding RNA Is Regulating <italic toggle="yes">Legionella pneumophila</italic> Hfq Expression in a Life Cycle-Dependent Manner

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