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  • 1
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    Online Resource
    The Integrity of the Cell Wall and Its Remodeling during Heterocyst Differentiation Are Regulated by Phylogenetically Conserved Small RNA Yfr1 in Nostoc sp. Strain PCC 7120
    American Society for Microbiology ; 2020
    In:  mBio Vol. 11, No. 1 ( 2020-02-25)
    Details
    In: mBio, American Society for Microbiology, Vol. 11, No. 1 ( 2020-02-25)
    Abstract: Yfr1 is a strictly conserved small RNA in cyanobacteria. A bioinformatic prediction to identify possible interactions of Yfr1 with mRNAs was carried out by using the sequences of Yfr1 from several heterocyst-forming strains, including Nostoc sp. strain PCC 7120. The results of the prediction were enriched in genes encoding outer membrane proteins and enzymes related to peptidoglycan biosynthesis and turnover. Heterologous expression assays with Escherichia coli demonstrated direct interactions of Yfr1 with mRNAs of 11 of the candidate genes. The expression of 10 of them ( alr2458 , alr4550 , murC , all4829 , all2158 , mraY , alr2269 , alr0834 , conR , patN ) was repressed by interaction with Yfr1, whereas the expression of amiC2 , encoding an amidase, was increased. The interactions between Yfr1 and the 11 mRNAs were confirmed by site-directed mutagenesis of Yfr1. Furthermore, a Nostoc strain with reduced levels of Yfr1 had larger amounts of mraY and murC mRNAs, supporting a role for Yfr1 in the regulation of those genes. Nostoc strains with either reduced or increased expression of Yfr1 showed anomalies in cell wall completion and were more sensitive to vancomycin than the wild-type strain. Furthermore, growth in the absence of combined nitrogen, which involves the differentiation of heterocysts, was compromised in the strain overexpressing Yfr1, and filaments were broken at the connections between vegetative cells and heterocysts. These results indicate that Yfr1 is an important regulator of cell wall homeostasis and correct cell wall remodeling during heterocyst differentiation. IMPORTANCE Bacterial small RNAs (sRNAs) are important players affecting the regulation of essentially every aspect of bacterial physiology. The cell wall is a highly dynamic structure that protects bacteria from their fluctuating environment. Cell envelope remodeling is particularly critical for bacteria that undergo differentiation processes, such as spore formation or differentiation of heterocysts. Heterocyst development involves the deposition of additional layers of glycolipids and polysaccharides outside the outer membrane. Here, we show that a cyanobacterial phylogenetically conserved small regulatory RNA, Yfr1, coordinates the expression of proteins involved in cell wall-related processes, including peptidoglycan metabolism and transport of different molecules, as well as expression of several proteins involved in heterocyst differentiation.
    Type of Medium: Online Resource
    ISSN: 2161-2129 , 2150-7511
    URL: Article
    DOI: 10.1128/mBio.02599-19
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2020
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  • 2
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    Online Resource
    The PTS Ntr -KdpDE-KdpFABC Pathway Contributes to Low Potassium Stress Adaptation and Competitive Nodulation of Sinorhizobium fredii
    American Society for Microbiology ; 2022
    In:  mBio Vol. 13, No. 3 ( 2022-06-28)
    Details
    In: mBio, American Society for Microbiology, Vol. 13, No. 3 ( 2022-06-28)
    Abstract: The rhizobium-legume symbiosis is essential for sustainable agriculture by reducing nitrogen fertilizer input, but its efficiency varies under fluctuating soil conditions and resources. The nitrogen-related phosphotransferase system (PTS Ntr ) consisting of PtsP, PtsO, and PtsN is required for optimal nodulation and nitrogen fixation efficiency of the broad-host-range Sinorhizobium fredii CCBAU45436 associated with diverse legumes, though the underlying mechanisms remain elusive. This work characterizes the PtsN-KdpDE-KdpFABC pathway that contributes to low potassium adaptation and competitive nodulation of CCBAU45436. Among three PtsN, PtsN 1 is the major functional homolog. The unphosphorylated PtsN 1 binds the sensory kinase KdpD through a non-canonical interaction with the GAF domain of KdpD, while the region covering HisKA-HATPase domains mediates the interaction of KdpD with the response regulator KdpE. KdpE directly activates the kdpFABC operon encoding the conserved high-affinity potassium uptake system. Disruption of this signaling pathway leads to reduced nodule number, nodule occupancy, and low potassium adaptation ability, but without notable effects on rhizoplane colonization. The induction of key nodulation genes NIN and ENOD40 in host roots during early symbiotic interactions is impaired when inoculating the kdpBC mutant that shows delayed nodulation. The nodulation defect of the kdpBC mutant can be rescued by supplying replete potassium. Potassium is actively consumed by both prokaryotes and eukaryotes, and components of the PTS Ntr -KdpDE-KdpFABC pathway are widely conserved in bacteria, highlighting the global importance of this pathway in bacteria-host interactions. IMPORTANCE In all ecological niches, potassium is actively consumed by diverse prokaryotes and their interacting eukaryote hosts. It is only just emerging that potassium is a key player in host-pathogen interactions, and the role of potassium in mutualistic interactions remains largely unknown. This work is focused on the mutualistic symbiosis between rhizobia and legumes. We report that the nitrogen-related phosphotransferase system PTS Ntr , the two-component system KdpDE, and the high-affinity potassium uptake system KdpFABC constitute a pathway that is important for low potassium adaptation and optimal nodulation of rhizobia. Given the widely conserved PTS Ntr , KdpDE, and KdpFABC in bacteria and increasing knowledge on microbiome for various niches, the PTS Ntr -KdpDE-KdpFABC pathway can be globally important in the biosphere.
    Type of Medium: Online Resource
    ISSN: 2150-7511
    URL: Article
    DOI: 10.1128/mbio.03721-21
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2022
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  • 3
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    Regulatory Effects of CsrA in Vibrio cholerae
    American Society for Microbiology ; 2021
    In:  mBio Vol. 12, No. 1 ( 2021-02-23)
    Details
    In: mBio, American Society for Microbiology, Vol. 12, No. 1 ( 2021-02-23)
    Abstract: CsrA is a posttranscriptional global regulator in Vibrio cholerae . Although CsrA is critical for V. cholerae survival within the mammalian host, the regulatory targets of CsrA remain mostly unknown. To identify pathways controlled by CsrA, RNA-seq transcriptome analysis was carried out by comparing the wild type and the csrA mutant grown to early exponential, mid-exponential, and stationary phases of growth. This enabled us to identify the global effects of CsrA-mediated regulation throughout the V. cholerae growth cycle. We found that CsrA regulates 22% of the V. cholerae transcriptome, with significant regulation within the gene ontology (GO) processes that involve amino acid transport and metabolism, central carbon metabolism, lipid metabolism, iron uptake, and flagellum-dependent motility. Through CsrA-RNA coimmunoprecipitation experiments, we found that CsrA binds to multiple mRNAs that encode regulatory proteins. These include transcripts encoding the major sigma factors RpoS and RpoE, which may explain how CsrA regulation affects such a large proportion of the V. cholerae transcriptome. Other direct targets include flrC , encoding a central regulator in flagellar gene expression, and aphA , encoding the virulence gene transcription factor AphA. We found that CsrA binds to the aphA mRNA both in vivo and in vitro , and CsrA significantly increases AphA protein synthesis. The increase in AphA was due to increased translation, not transcription, in the presence of CsrA, consistent with CsrA binding to the aphA transcript and enhancing its translation. CsrA is required for the virulence of V. cholerae and this study illustrates the central role of CsrA in virulence gene regulation. IMPORTANCE Vibrio cholerae , a Gram-negative bacterium, is a natural inhabitant of the aqueous environment. However, once ingested, this bacterium can colonize the human host and cause the disease cholera. In order to successfully transition between its aqueous habitat and the human host, the bacterium must sense changes in its environment and rapidly alter gene expression. Global regulators, including CsrA, play an integral role in altering the expression of a large number of genes to promote adaptation and survival, which is required for intestinal colonization. We used transcriptomics and a directed CsrA-RNA coimmunoprecipitation to characterize the CsrA regulon and found that CsrA alters the expression of more than 800 transcripts in V. cholerae . Processes regulated by CsrA include motility, the rugose phenotype, and virulence pathways. CsrA directly binds to the aphA transcript and positively regulates the production of the virulence regulator AphA. Thus, CsrA regulates multiple processes that have been linked to pathogenesis.
    Type of Medium: Online Resource
    ISSN: 2161-2129 , 2150-7511
    URL: Article
    DOI: 10.1128/mBio.03380-20
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2021
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  • 4
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    Conservation of Transcription Start Sites within Genes across a Bacterial Genus
    American Society for Microbiology ; 2014
    In:  mBio Vol. 5, No. 4 ( 2014-08-29)
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    In: mBio, American Society for Microbiology, Vol. 5, No. 4 ( 2014-08-29)
    Abstract: The first step of gene expression is the initiation of transcription from promoters, which have been traditionally thought to be located upstream of genes. Recently, studies showed that in diverse bacteria, promoters are often located inside genes. It has not been clear if these unexpected promoters are important to the organism or if they result from transcriptional noise. Here, we identify and examine promoters in eight related bacterial species. Promoters that lie within genes on the sense strand are often conserved as locations and in their sequences. Furthermore, these promoters often affect the bacterium’s growth. Thus, many of these unexpected promoters are likely functional. Fewer promoters that lie within genes on the antisense strand are conserved, but the conserved ones seem to drive the expression of nearby genes.
    Type of Medium: Online Resource
    ISSN: 2161-2129 , 2150-7511
    URL: Article
    DOI: 10.1128/mBio.01398-14
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2014
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  • 5
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    Temperature, by Controlling Growth Rate, Regulates CRISPR-Cas Activity in Pseudomonas aeruginosa
    American Society for Microbiology ; 2018
    In:  mBio Vol. 9, No. 6 ( 2018-12-21)
    Details
    In: mBio, American Society for Microbiology, Vol. 9, No. 6 ( 2018-12-21)
    Abstract: Clustered regularly interspaced short palindromic repeat (CRISPR)-associated (CRISPR-Cas) systems are adaptive defense systems that protect bacteria and archaea from invading genetic elements. In Pseudomonas aeruginosa , quorum sensing (QS) induces the CRISPR-Cas defense system at high cell density when the risk of bacteriophage infection is high. Here, we show that another cue, temperature, modulates P. aeruginosa CRISPR-Cas. Increased CRISPR adaptation occurs at environmental (i.e., low) temperatures compared to that at body (i.e., high) temperature. This increase is a consequence of the accumulation of CRISPR-Cas complexes, coupled with reduced P. aeruginosa growth rate at the lower temperature, the latter of which provides additional time prior to cell division for CRISPR-Cas to patrol the cell and successfully eliminate and/or acquire immunity to foreign DNA. Analyses of a QS mutant and synthetic QS compounds show that the QS and temperature cues act synergistically. The diversity and level of phage encountered by P. aeruginosa in the environment exceed that in the human body, presumably warranting increased reliance on CRISPR-Cas at environmental temperatures. IMPORTANCE P. aeruginosa is a soil dwelling bacterium and a plant pathogen, and it also causes life-threatening infections in humans. Thus, P. aeruginosa thrives in diverse environments and over a broad range of temperatures. Some P. aeruginosa strains rely on the CRISPR-Cas adaptive immune system as a phage defense mechanism. Our discovery that low temperatures increase CRISPR adaptation suggests that the rarely occurring but crucial naive adaptation events may take place predominantly under conditions of slow growth, e.g., during the bacterium’s soil dwelling existence and during slow growth in biofilms.
    Type of Medium: Online Resource
    ISSN: 2161-2129 , 2150-7511
    URL: Article
    DOI: 10.1128/mBio.02184-18
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2018
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  • 6
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    Secreted Proteases Control the Timing of Aggregative Community Formation in Vibrio cholerae
    American Society for Microbiology ; 2021
    In:  mBio Vol. 12, No. 6 ( 2021-12-21)
    Details
    In: mBio, American Society for Microbiology, Vol. 12, No. 6 ( 2021-12-21)
    Abstract: Bacteria orchestrate collective behaviors using the cell-cell communication process called quorum sensing (QS). QS relies on the synthesis, release, and group-wide detection of small molecules called autoinducers. In Vibrio cholerae , a multicellular community aggregation program occurs in liquid, during the stationary phase, and in the high-cell-density QS state. Here, we demonstrate that this aggregation program consists of two subprograms. In one subprogram, which we call void formation, structures form that contain few cells but provide a scaffold within which cells can embed. The other subprogram relies on flagellar machinery and enables cells to enter voids. A genetic screen for factors contributing to void formation, coupled with companion molecular analyses, showed that four extracellular proteases, Vca0812, Vca0813, HapA, and PrtV, control the onset timing of both void formation and aggregation; moreover, proteolytic activity is required. These proteases, or their downstream products, can be shared between void-producing and non-void-forming cells and can elicit aggregation in a normally nonaggregating V. cholerae strain. Employing multiple proteases to control void formation and aggregation timing could provide a redundant and irreversible path to commitment to this community lifestyle. IMPORTANCE Bacteria can work as collectives to form multicellular communities. Vibrio cholerae , the bacterium that causes the disease cholera in humans, forms aggregated communities in liquid. Aggregate formation relies on a chemical communication process called quorum sensing. Here, we show that, beyond overarching control by quorum sensing, there are two aggregation subprograms. One subprogram, which we call void formation, creates a scaffold within which cells can embed. The second subprogram, which allows bacteria to enter the scaffold, requires motility. We discovered that four extracellular proteases control the timing of both void formation and aggregation. We argue that, by using redundant proteases, V. cholerae ensures the reliable execution of this community formation process. These findings may provide insight into how V. cholerae persists in the marine environment or colonizes the human host, as both lifestyles are central to the spread of the disease cholera.
    Type of Medium: Online Resource
    ISSN: 2150-7511
    URL: Article
    DOI: 10.1128/mBio.01518-21
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2021
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  • 7
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    Pervasive RNA Regulation of Metabolism Enhances the Root Colonization Ability of Nitrogen-Fixing Symbiotic α-Rhizobia
    American Society for Microbiology ; 2022
    In:  mBio Vol. 13, No. 1 ( 2022-02-22)
    Details
    In: mBio, American Society for Microbiology, Vol. 13, No. 1 ( 2022-02-22)
    Abstract: The rhizosphere and rhizoplane are nutrient-rich but selective environments for the root microbiome. Here, we deciphered a posttranscriptional network regulated by the homologous trans -small RNAs (sRNAs) AbcR1 and AbcR2, which rewire the metabolism of the nitrogen-fixing α-rhizobium Sinorhizobium meliloti during preinfection stages of symbiosis with its legume host alfalfa. The LysR-type regulator LsrB, which transduces the cell redox state, is indispensable for AbcR1 expression in actively dividing bacteria, whereas the stress-induced transcription of AbcR2 depends on the alternative σ factor RpoH1. MS2 affinity purification coupled with RNA sequencing unveiled exceptionally large and overlapping AbcR1/2 mRNA interactomes, jointly representing ⁓6% of the S. meliloti protein-coding genes. Most mRNAs encode transport/metabolic proteins whose translation is silenced by base pairing to two distinct anti-Shine Dalgarno motifs that function independently in both sRNAs. A metabolic model-aided analysis of the targetomes predicted changes in AbcR1/2 expression driven by shifts in carbon/nitrogen sources, which were confirmed experimentally. Low AbcR1/2 levels in some defined media anticipated overexpression growth phenotypes linked to the silencing of specific mRNAs. As a proof of principle, we confirmed AbcR1/2-mediated downregulation of the l -amino acid AapQ permease. AbcR1/2 interactomes are well represented in rhizosphere-related S. meliloti transcriptomic signatures. Remarkably, a lack of AbcR1 specifically compromised the ability of S. meliloti to colonize the root rhizoplane. The AbcR1 regulon likely ranks the utilization of available substrates to optimize metabolism, thus conferring on S. meliloti an advantage for efficient rhizosphere/rhizoplane colonization. AbcR1 regulation is predicted to be conserved in related α-rhizobia, which opens unprecedented possibilities for engineering highly competitive biofertilizers. IMPORTANCE Nitrogen-fixing root nodule symbioses between rhizobia and legume plants provide more than half of the combined nitrogen incorporated annually into terrestrial ecosystems, rendering plant growth independent of environmentally unfriendly chemical fertilizers. The success of symbiosis depends primarily on the capacity of rhizobia to establish competitive populations in soil and rhizosphere environments. Here, we provide insights into the regulation and architecture of an extensive RNA posttranscriptional network that fine-tunes the metabolism of the alfalfa symbiont S. meliloti , thereby enhancing the ability of this beneficial bacterium to colonize nutrient-rich but extremely selective niches, such as the rhizosphere of its host plant. This pervasive RNA regulation of metabolism is a major adaptive mechanism, predicted to operate in diverse rhizobial species. Because RNA regulation relies on modifiable base-pairing interactions, our findings open unexplored avenues for engineering the legumes rhizobiome within sustainable agricultural practices.
    Type of Medium: Online Resource
    ISSN: 2150-7511
    URL: Article
    DOI: 10.1128/mbio.03576-21
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2022
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  • 8
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    Online Resource
    Integration of the Salmonella Typhimurium Methylome and Transcriptome Reveals That DNA Methylation and Transcriptional Regulation Are Largely Decoupled under Virulence-Related Conditions
    American Society for Microbiology ; 2022
    In:  mBio Vol. 13, No. 3 ( 2022-06-28)
    Details
    In: mBio, American Society for Microbiology, Vol. 13, No. 3 ( 2022-06-28)
    Abstract: Despite being in a golden age of bacterial epigenomics, little work has systematically examined the plasticity and functional impacts of the bacterial DNA methylome. Here, we leveraged single-molecule, real-time sequencing (SMRT-seq) to examine the m 6 A DNA methylome of two Salmonella enterica serovar Typhimurium strains: 14028s and a Δ metJ mutant with derepressed methionine metabolism, grown in Luria broth or medium that simulates the intracellular environment. We found that the methylome is remarkably static: 〉 95% of adenosine bases retain their methylation status across conditions. Integration of methylation with transcriptomic data revealed limited correlation between changes in methylation and gene expression. Further, examination of the transcriptome in Δ yhdJ bacteria lacking the m 6 A methylase with the most dynamic methylation pattern in our data set revealed little evidence of YhdJ-mediated gene regulation. Curiously, despite G(m 6 A)TC motifs being particularly resistant to change across conditions, incorporating dam mutants into our analyses revealed two examples where changes in methylation and transcription may be linked across conditions. This includes the novel finding that the Δ metJ motility defect may be partially driven by hypermethylation of the chemotaxis gene tsr . Together, these data redefine the S. Typhimurium epigenome as a highly stable system that has rare but important roles in transcriptional regulation. Incorporating these lessons into future studies will be critical as we progress through the epigenomic era. IMPORTANCE While recent breakthroughs have enabled intense study of bacterial DNA modifications, limitations in current work have potentiated a surprisingly untested narrative that DNA methylation is a common mechanism of the bacterial response to environmental conditions. Essentially, whether epigenetic regulation of bacterial transcription is a common, generalizable phenomenon is a critical unanswered question that we address here. We found that most DNA methylation is static in Salmonella enterica serovar Typhimurium, even when the bacteria are grown under dramatically different conditions that cause broad changes in the transcriptome. Further, even when the methylation of individual bases change, these changes generally do not correlate with changes in gene expression. Finally, we demonstrate methods by which data can be stratified in order to identify coupled changes in methylation and gene expression.
    Type of Medium: Online Resource
    ISSN: 2150-7511
    URL: Article
    DOI: 10.1128/mbio.03464-21
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2022
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  • 9
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    Online Resource
    Identification of Attenuators of Transcriptional Termination: Implications for RNA Regulation in Escherichia coli
    American Society for Microbiology ; 2022
    In:  mBio Vol. 13, No. 6 ( 2022-12-20)
    Details
    In: mBio, American Society for Microbiology, Vol. 13, No. 6 ( 2022-12-20)
    Abstract: The regulatory function of many bacterial small RNAs (sRNAs) requires the binding of the RNA chaperone Hfq to the 3′ portion of the sRNA intrinsic terminator, and therefore sRNA signaling might be regulated by modulating its terminator. Here, using a multicopy screen developed with the terminator of sRNA SgrS, we identified an sRNA gene ( cyaR ) and three protein-coding genes ( cspD , ygjH , and rof ) that attenuate SgrS termination in Escherichia coli . Analyses of CyaR and YgjH, a putative tRNA binding protein, suggested that the CyaR activity was indirect and the effect of YgjH was moderate. Overproduction of the protein attenuators CspD and Rof resulted in more frequent readthrough at terminators of SgrS and two other sRNAs, and regulation by SgrS of target mRNAs was reduced. The effect of Rof, a known inhibitor of Rho, was mimicked by bicyclomycin or by a rho mutant, suggesting an unexpected role for Rho in sRNA termination. CspD, a member of the cold shock protein family, bound both terminated and readthrough transcripts, stabilizing them and attenuating termination. By RNA sequencing analysis of the CspD overexpression strain, we found global effects of CspD on gene expression across some termination sites. We further demonstrated effects of endogenous CspD under slow growth conditions where cspD is highly expressed. These findings provided evidence of changes in the efficiency of intrinsic termination, confirming this as an additional layer of the regulation of sRNA signaling. IMPORTANCE Growing evidence suggests that the modulation of intrinsic termination and readthrough of transcription is more widespread than previously appreciated. For small RNAs, proper termination plays a critical role in their regulatory function. Here, we present a multicopy screen approach to identify factors that attenuate small RNA termination and therefore abrogate signaling dependent on the small RNA. This study highlights a new aspect of regulation of small RNA signaling as well as the modulation of intrinsic termination.
    Type of Medium: Online Resource
    ISSN: 2150-7511
    URL: Article
    DOI: 10.1128/mbio.02371-22
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2022
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  • 10
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    A Small Regulatory RNA Controls Cell Wall Biosynthesis and Antibiotic Resistance
    American Society for Microbiology ; 2018
    In:  mBio Vol. 9, No. 6 ( 2018-12-21)
    Details
    In: mBio, American Society for Microbiology, Vol. 9, No. 6 ( 2018-12-21)
    Abstract: Small regulatory RNAs play an important role in the adaptation to changing conditions. Here, we describe a differentially expressed small regulatory RNA (sRNA) that affects various cellular processes in the plant pathogen Agrobacterium tumefaciens . Using a combination of bioinformatic predictions and comparative proteomics, we identified nine targets, most of which are positively regulated by the sRNA. According to these targets, we named the sRNA PmaR for peptidoglycan biosynthesis, motility, and ampicillin resistance regulator. Agrobacterium spp. are long known to be naturally resistant to high ampicillin concentrations, and we can now explain this phenotype by the positive PmaR-mediated regulation of the beta-lactamase gene ampC . Structure probing revealed a spoon-like structure of the sRNA, with a single-stranded loop that is engaged in target interaction in vivo and in vitro . Several riboregulators have been implicated in antibiotic resistance mechanisms, such as uptake and efflux transporters, but PmaR represents the first example of an sRNA that directly controls the expression of an antibiotic resistance gene. IMPORTANCE The alphaproteobacterium Agrobacterium tumefaciens is able to infect various eudicots causing crown gall tumor formation. Based on its unique ability of interkingdom gene transfer, Agrobacterium serves as a crucial biotechnological tool for genetic manipulation of plant cells. The presence of hundreds of putative sRNAs in this organism suggests a considerable impact of riboregulation on A. tumefaciens physiology. Here, we characterized the biological function of the sRNA PmaR that controls various processes crucial for growth, motility, and virulence. Among the genes directly targeted by PmaR is ampC coding for a beta-lactamase that confers ampicillin resistance, suggesting that the sRNA is crucial for fitness in the competitive microbial composition of the rhizosphere.
    Type of Medium: Online Resource
    ISSN: 2161-2129 , 2150-7511
    URL: Article
    DOI: 10.1128/mBio.02100-18
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2018
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