Browsing by Author "Tamman, Hedvig"

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    The GraTA toxin-antitoxin system of Pseudomonas putida: regulation and role in stress tolerance
    (2016-09-19) Tamman, Hedvig; Hõrak, Rita, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond.
    Elu on stressirohke, eriti üheraksetel organismidel nagu bakterid. Sageli tundub, et parim viis stressiga toimetulekuks on rahulikult oodata tingimuste paranemist. Selline käitumismall on kasutust leidnud ka mikroobide maailmas. Bakteritel on palju erinevaid kasvu reguleerimise võimalusi, mille hulka on viimasel ajal arvatud ka toksiin-antitoksiin (TA) süsteemid. TA-süsteemid koosnevad kahest komponendist: rakule eluliselt olulisi protsesse või rakukesta kahjustavast toksiinist ja teda neutraliseerivast antitoksiinist. Selliste geenide olemasolu bakterite genoomis on esmapilgul mõistatuslik, sest miks peaks bakter tootma iseendale toksilist valku? Hiljutised uuringud mikroobide mudelorganismis Escherichia coli on näidanud, et toksiinid põhjustavad bakterite üleminekut uinuvasse olekusse, mida iseloomustab bakterite ainevahetuse aeglustumine ja peatunud kasv. Sellised mikroobid tekitavad suuri probleeme meditsiinis, kuna on väga paljude stressiolukordade, kaasa arvatud paljude antibiootikumide toime suhtes tundetumad ja võimelised üle elama tingimusi, mis kiirelt kasvavaid baktereid tapaks. Kui mudelorganismis E. coli on TA süsteemide osalus bakteri stressitaluvuses hästi kirjeldatud, siis teistes bakteriliikides ei ole neid potentsiaalselt toksilisi süsteeme nii süstemaatiliselt uuritud. Seetõttu ei ole ka selge, kas erinevates bakterites toimivad TA süsteemid erinevalt või mingi üldise mehhanismi alusel. Käesolev töö kirjeldab keskkonnabakteri Pseudomonas putida kasvukiirust mõjutavat GraTA süsteemi. Tavaliselt takistab antitoksiin GraA väga efektiivselt toksiini GraT aktiivsust, kuid antitoksiinist vabanenult suudab toksiin mõjutada selle bakteri stressitaluvust. Toksiini mõju on kahetine, sest olenevalt stressi tüübist võib toksiin nii suurendada kui ka vähendada bakteri stressitaluvust. Seetõttu on bakterile väga oluline, et potentsiaalselt kahjulik TA süsteem aktiveeruks vaid kindlatel stressitingimustel.
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    Isolation and characterization of a phage collection against Pseudomonas putida
    (2024-06-11) Brauer, Age; Rosendahl, Sirli; Kängsep, Anu; Lewańczyk, Alicja Cecylia; Rikberg, Roger; Hõrak, Rita; Tamman, Hedvig
    The environmental bacterium, Pseudomonas putida, possesses a broad spectrum of metabolic pathways. This makes it highly promising for use in biotechnological production as a cell factory, as well as in bioremediation strategies to degrade various aromatic pollutants. For P. putida to flourish in its environment, it must withstand the continuous threats posed by bacteriophages. Interestingly, until now, only a handful of phages have been isolated for the commonly used laboratory strain, P. putida KT2440, and no phage defence mechanisms have been characterized. In this study, we present a new Collection of Environmental P. putida Phages from Estonia, or CEPEST. This collection comprises 67 double-stranded DNA phages, which belong to 22 phage species and 9 phage genera. Our findings reveal that most phages in the CEPEST collection are more infectious at lower temperatures, have a narrow host range, and require an intact lipopolysaccharide for P. putida infection. Furthermore, we show that cryptic prophages present in the P. putida chromosome provide strong protection against the infection of many phages. However, the chromosomal toxin–antitoxin systems do not play a role in the phage defence of P. putida. This research provides valuable insights into the interactions between P. putida and bacteriophages, which could have significant implications for biotechnological and environmental applications.
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    RelA-SpoT Homolog toxins pyrophosphorylate the CCA end of tRNA to inhibit protein synthesis
    (Cell Press, 2021-08) Brodiazhenko, Tetiana; Alves Oliveira, Sofia Raquel; Roghanian, Mohammad; Sakaguchi, Yuriko; Turnbull, Kathryn Jane; Bulvas, Ondrej; Takada, Hiraku; Tamman, Hedvig; Ainelo, Andres; Pohl, Radek; Rejman, Dominik; Tenson, Tanel; Suzuki, Tsutomu; Garcia-Pino, Abel; Atkinson, Gemma C; Haurilyiuk, Vasili; Kurata, Tatsuki
    RelA-SpoT Homolog (RSH) enzymes control bacterial physiology through synthesis and degradation of the nucleotide alarmone (p)ppGpp. We recently discovered multiple families of small alarmone synthetase (SAS) RSH acting as toxins of toxin-antitoxin (TA) modules, with the FaRel subfamily of toxSAS abrogating bacterial growth by producing an analog of (p)ppGpp, (pp)pApp. Here we probe the mechanism of growth arrest used by four experimentally unexplored subfamilies of toxSAS: FaRel2, PhRel, PhRel2, and CapRel. Surprisingly, all these toxins specifically inhibit protein synthesis. To do so, they transfer a pyrophosphate moiety from ATP to the tRNA 3′ CCA. The modification inhibits both tRNA aminoacylation and the sensing of cellular amino acid starvation by the ribosome-associated RSH RelA. Conversely, we show that some small alarmone hydrolase (SAH) RSH enzymes can reverse the pyrophosphorylation of tRNA to counter the growth inhibition by toxSAS. Collectively, we establish RSHs as RNA-modifying enzymes.
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