Conjugation Dynamics of Self-Transmissible and Mobilisable Plasmids into E. coli O157:H7 on Arabidopsis thaliana Rosettes.

Many antibiotic resistance genes present in human pathogenic bacteria are believed to originate from environmental bacteria. Conjugation of antibiotic resistance conferring plasmids is considered to be one of the major reasons for the increasing prevalence of antibiotic resistances. A hotspot for plasmid-based horizontal gene transfer is the phyllosphere, i.e., the surfaces of aboveground plant parts. Bacteria in the phyllosphere might serve as intermediate hosts with transfer capability to human pathogenic bacteria. In this study, the exchange of mobilisable and self-transmissible plasmids via conjugation was evaluated. The conjugation from the laboratory strain Escherichia coli S17-1, the model phyllosphere coloniser Pantoea eucalypti 299R, and the model pathogen E. coli O157:H7 to the recipient strain E. coli O157:H7::MRE103 (EcO157:H7red) in the phyllosphere of Arabidopsis thaliana was determined. The results suggest that short-term occurrence of a competent donor is sufficient to fix plasmids in a recipient population of E. coli O157:H7red. The spread of self-transmissible plasmids was limited after initial steep increases of transconjugants that contributed up to 10% of the total recipient population. The here-presented data of plasmid transfer will be important for future modelling approaches to estimate environmental spread of antibiotic resistance in agricultural production environments.

Post-transcriptional control of executioner caspases by RNA-binding proteins.

Caspases are key components of apoptotic pathways. Regulation of caspases occurs at several levels, including transcription, proteolytic processing, inhibition of enzymatic function, and protein degradation. In contrast, little is known about the extent of post-transcriptional control of caspases. Here, we describe four conserved RNA-binding proteins (RBPs)-PUF-8, MEX-3, GLD-1, and CGH-1-that sequentially repress the CED-3 caspase in distinct regions of the Caenorhabditis elegans germline. We demonstrate that GLD-1 represses ced-3 mRNA translation via two binding sites in its 3' untranslated region (UTR), thereby ensuring a dual control of unwanted cell death: at the level of p53/CEP-1 and at the executioner caspase level. Moreover, we identified seven RBPs that regulate human caspase-3 expression and/or activation, including human PUF-8, GLD-1, and CGH-1 homologs PUM1, QKI, and DDX6. Given the presence of unusually long executioner caspase 3' UTRs in many metazoans, translational control of executioner caspases by RBPs might be a strategy used widely across the animal kingdom to control apoptosis.

MiniTn7-transposon delivery vectors for inducible or constitutive fluorescent protein expression in Enterobacteriaceae.

Here we present the generation and function of two sets of bacterial plasmids that harbor fluorescent genes encoding either blue, cyan, yellow or red fluorescent proteins. In the first set, protein expression is controlled by the strong and constitutive nptII promoter whereas in the second set, the strong tac promoter was chosen that underlies LacI(q) regulation. Furthermore, the plasmids are mobilizable, contain Tn7 transposons and a temperature-sensitive origin of replication. Using Escherichia coli S17-1 as donor strain, the plasmids allow fast and convenient Tn7-transposon delivery into many enterobacterial hosts, such as the here-used E. coli O157:H7. This procedure omits the need of preparing competent recipient cells and antibiotic resistances are only transiently conferred to the recipients. As the fluorescence proteins show little to no overlap in fluorescence emission, the constructs are well suited for the study of multicolored synthetic bacterial communities during biofilm production or in host colonization studies, e.g. of plant surfaces. Furthermore, tac promoter-reporter constructs allow the generation of so-called reproductive success reporters, which allow to estimate past doublings of bacterial individuals after introduction into environments, emphasizing the role of individual cells during colonization.