No Genotoxicity Is Detectable for Strain Nissle 1917 by Standard In Vitro and In Vivo Tests.

Probiotic strain Nissle 1917 (EcN) has a long history of safe use. However, the recently discovered presence of a locus in its genome presumably producing colibactin has questioned its safety, as colibactin has been implicated in genotoxicity. Here, we assess the genotoxic potential of EcN.

One gene, two proteins: coordinated production of a copper chaperone by differential transcript formation and translational frameshifting in Escherichia coli.

Programmed ribosomal frameshifting (PRF) is a translational anomaly causing the ribosome to shift into an alternative reading frame. PRFs are common in viral genomes, using a single nucleotide sequence to code for two proteins in overlapping frames. In bacteria and eukaryota, PRFs are less frequent.

Constitutive production of c-di-GMP is associated with mutations in a variant of Pseudomonas aeruginosa with altered membrane composition.

Most bacteria can form multicellular communities called biofilms on biotic and abiotic surfaces. This multicellular response to surface contact correlates with an increased resistance to various adverse environmental conditions, including those encountered during infections of the human host and exposure to antimicrobial compounds. Biofilm formation occurs when freely swimming (planktonic) cells encounter a surface, which stimulates the chemosensory-like, surface-sensing system Wsp and leads to generation of the intracellular second messenger 3',5'-cyclic-di-guanosine monophosphate (c-di-GMP).

The PqsR and RhlR transcriptional regulators determine the level of Pseudomonas quinolone signal synthesis in Pseudomonas aeruginosa by producing two different pqsABCDE mRNA isoforms.

Regulation of gene expression plays a key role in bacterial adaptability to changes in the environment. An integral part of this gene regulatory network is achieved via quorum sensing (QS) systems that coordinate bacterial responses under high cellular densities. In the nosocomial pathogen Pseudomonas aeruginosa, the 2-alkyl-4-quinolone (pqs) signaling pathway is crucial for bacterial survival under stressful conditions.

Translational control of small heat shock genes in mesophilic and thermophilic cyanobacteria by RNA thermometers.

Cyanobacteria constitute a heterogeneous phylum of oxygen-producing, photosynthetic prokaryotes. They are susceptible to various stress conditions like heat, salt, or light stress, all inducing the cyanobacterial heat shock response (HSR). Cyanobacterial small heat shock proteins (sHsps) are known to preserve thylakoid membrane integrity under stress conditions, thereby protecting the photosynthesis machinery.

Evolution from the prokaryotic to the higher plant chloroplast signal recognition particle: the signal recognition particle RNA is conserved in plastids of a wide range of photosynthetic organisms.

The protein targeting signal recognition particle (SRP) pathway in chloroplasts of higher plants has undergone dramatic evolutionary changes. It disposed of its RNA, which is an essential SRP component in bacteria, and uses a unique chloroplast-specific protein cpSRP43. Nevertheless, homologs of the conserved SRP54 and the SRP receptor, FtsY, are present in higher plant chloroplasts.

Transcriptional and posttranscriptional events control copper-responsive expression of a Rhodobacter capsulatus multicopper oxidase.

The copper-regulated Rhodobacter capsulatus cutO (multicopper oxidase) gene confers copper tolerance and is carried in the tricistronic orf635-cutO-cutR operon. Transcription of cutO strictly depends on the promoter upstream of orf635, as demonstrated by lacZ reporter fusions to nested promoter fragments. Remarkably, orf635 expression was not affected by copper availability, whereas cutO and cutR were expressed only in the presence of copper.

Thermogenetic tools to monitor temperature-dependent gene expression in bacteria.

Free-living bacteria constantly monitor their ambient temperature. Drastic deviations elicit immediate protective responses known as cold shock or heat shock response. Many mammalian pathogens use temperature surveillance systems to recognize the successful invasion of a host by its body temperature, usually 37°C.

Modulation of the stability of the Salmonella fourU-type RNA thermometer.

RNA thermometers are translational control elements that regulate the expression of bacterial heat shock and virulence genes. They fold into complex secondary structures that block translation at low temperatures. A temperature increase releases the ribosome binding site and thus permits translation initiation.

Direct observation of the temperature-induced melting process of the Salmonella fourU RNA thermometer at base-pair resolution.

In prokaryotes, RNA thermometers regulate a number of heat shock and virulence genes. These temperature sensitive RNA elements are usually located in the 5'-untranslated regions of the regulated genes. They repress translation initiation by base pairing to the Shine-Dalgarno sequence at low temperatures.

Microbial thermosensors.

Temperature is among the most important of the parameters that free-living microbes monitor. Microbial physiology needs to be readjusted in response to sudden temperature changes. When the ambient temperature rises or drops to potentially harmful levels, cells mount protective stress responses--so-called heat or cold shock responses, respectively.

The Escherichia coli ibpA thermometer is comprised of stable and unstable structural elements.

Translation of many small heat shock genes in alpha- and gamma-proteobacteria is controlled by the ROSE (Repression Of heat Shock gene Expression) element, a thermo-responsive RNA structure in the 5'-untranslated region. ROSE(ibpA) regulates translation of the Escherichia coli ibpA gene coding for an inclusion body-associated protein. We present first structural insights into a full-length ROSE element by examining the temperature-induced conformational changes of ROSE(ibpA) using detailed enzymatic and lead probing experiments between 20 and 50 degrees C.

Translation of chloroplast psbD mRNA in Chlamydomonas is controlled by a secondary RNA structure blocking the AUG start codon.

Translation initiation represents a key step during regulation of gene expression in chloroplasts. Here, we report on the identification and characterization of three suppressor point mutations which overcome a translational defect caused by the deletion of a U-rich element in the 5'-untranslated region (5'-UTR) of the psbD mRNA in the green alga Chlamydomonas reinhardtii. All three suppressors affect a secondary RNA structure encompassing the psbD AUG initiation codon within a double-stranded region as judged by the analysis of site-directed chloroplast mutants as well as in vitro RNA mapping experiments using RNase H.

Relationship between mRNA levels and protein accumulation in a chloroplast promoter-mutant of Chlamydomonas reinhardtii.

The photosynthetic chloroplast mutant G64 of Chlamydomonas reinhardtii was shown to contain a single point mutation within the 5' region of the psbD gene encoding the D2 protein of the photosystem II reaction center. The mutation affects the sequence element TATAATAT which has previously been hypothesized to function as the psbD promoter. Run-on analysis confirmed that transcription of psbD in the mutant was reduced to approximately 10% of the wild-type level.

PMT family of Candida albicans: five protein mannosyltransferase isoforms affect growth, morphogenesis and antifungal resistance.

Protein O-mannosyltransferases (Pmt proteins) initiate O-mannosylation of secretory proteins. The PMT gene family of the human fungal pathogen Candida albicans consists of PMT1 and PMT6, as well as three additional PMT genes encoding Pmt2, Pmt4 and Pmt5 isoforms described here. Both PMT2 alleles could not be deleted and growth of conditional strains, containing PMT2 controlled by the MET3- or tetOScHOP1-promoters, was blocked in non-permissive conditions, indicating that PMT2 is essential for growth.

PratA, a periplasmic tetratricopeptide repeat protein involved in biogenesis of photosystem II in Synechocystis sp. PCC 6803.

The light reactions of oxygenic photosynthesis are mediated by multisubunit pigment-protein complexes situated within the specialized thylakoid membrane system. The biogenesis of these complexes is regulated by transacting factors that affect the expression of the respective subunit genes and/or the assembly of their products. Here we report on the analysis of the PratA gene from the cyanobacterium Synechocystis sp.