Establishment of a Cre recombinase based mutagenesis protocol for markerless gene deletion in Streptococcus suis

Phage Therapy: What Have We Learned?

In this article we explain how current events in the field of phage therapy may positively influence its future development. We discuss the shift in position of the authorities, academia, media, non-governmental organizations, regulatory agencies, patients, and doctors which could enable further advances in the research and application of the therapy. In addition, we discuss methods to obtain optimal phage preparations and suggest the potential of novel applications of phage therapy extending beyond its anti-bacterial action.

The competence system of Streptococcus anginosus and its use for genetic engineering

Streptococcus anginosus is considered a human commensal but improvements in species identification in recent years have highlighted its role as an emerging pathogen. However, our knowledge about the pathogenicity mechanisms in this species is scarce. One reason for this is the lack of published genetic manipulation techniques in the S. anginosus group. To establish a novel mutation technique we investigated the competence system of S. anginosus and created a Cre-recombinase-based mutation method that allows the generation of markerless gene deletions in S. anginosus. In silico analysis of the competence system demonstrated that S. anginosus encodes homologues for the vast majority of genes that are known to be essential for the transformation of S. pneumoniae. Analysis of transformation kinetics confirmed that S. anginosus SK52 possesses an S. pneumoniae-like competence development with a rapid increase of competence after treatment with Competence Stimulating Peptide (CSP), reaching a maximum transformation efficiency of 0.24% ± 0.08%. The combination of CSP-induced transformation and the Cre-lox system allows the efficient and fast creation of markerless gene deletions and will facilitate the investigation of the pathogenicity of S. anginosus on a genetic level.

Establishment of a markerless multiple-gene deletion method based on Cre/loxP mutant system for Bacillus pumilus

In this study, we established a Cre/loxP mutant recombination system (Cre/lox71-66 system) for markerless gene deletion to facilitate our follow-up rational genetic engineering to the strain Bacillus pumilus W3. This modified method uses two mutant loxP sites, which after recombination creates a double-mutant loxP site that is poorly recognized by Cre recombinase, facilitating multiple gene deletions in a single genetic background. Two selected genes, cotA and sigF, were continuously knocked out and verified at different levels using this method. This method is simple and efficient and can be easily implemented for multiple gene deletions in B. pumilus.

The chromosomal SezAT toxin-antitoxin system promotes the maintenance of the SsPI-1 pathogenicity island in epidemic Streptococcus suis

Streptococcus suis has emerged as a causative agent of human meningitis and streptococcal toxic shock syndrome over the last years. The high pathogenicity of S. suis may be due in part to a laterally acquired pathogenicity island (renamed SsPI-1), which can spontaneously excise and transfer to recipients. Cells harboring excised SsPI-1 can potentially lose this island if cell division occurs prior to its reintegration; however, attempts to cure SsPI-1 from the host cells have been unsuccessful. Here, we report that an SsPI-1-borne Epsilon/Zeta toxin-antitoxin system (designated SezAT) promotes SsPI-1 stability in bacterial populations. The sezAT locus consists of two closely linked sezT and sezA genes encoding a toxin and its cognate antitoxin, respectively. Overproduction of SezT induces a bactericidal effect that can be neutralized by co-expression of SezA, but not by its later action. When devoid of a functional SezAT system, large-scale deletion of SsPI-1 is straightforward. Thus, SezAT serves to ensure inheritance of SsPI-1 during cell division, which may explain the persistence of epidemic S. suis. This report presents the first functional characterization of TA loci in S. suis, and the first biochemical evidence for the adaptive significance of the Epsilon/Zeta system in the evolution of pathogen virulence.

Characterization of the pivotal carbon metabolism of Streptococcus suis serotype 2 under ex vivo and chemically defined in vitro conditions by isotopologue profiling

Streptococcus suis is a neglected zoonotic pathogen that has to adapt to the nutritional requirements in the different host niches encountered during infection and establishment of invasive diseases. To dissect the central metabolic activity of S. suis under different conditions of nutrient availability, we performed labeling experiments starting from [(13)C]glucose specimens and analyzed the resulting isotopologue patterns in amino acids of S. suis grown under in vitro and ex vivo conditions. In combination with classical growth experiments, we found that S. suis is auxotrophic for Arg, Gln/Glu, His, Leu, and Trp in chemically defined medium. De novo biosynthesis was shown for Ala, Asp, Ser, and Thr at high rates and for Gly, Lys, Phe, Tyr, and Val at moderate or low rates, respectively. Glucose degradation occurred mainly by glycolysis and to a minor extent by the pentose phosphate pathway. Furthermore, the exclusive formation of oxaloacetate by phosphoenolpyruvate (PEP) carboxylation became evident from the patterns in de novo synthesized amino acids. Labeling experiments with S. suis grown ex vivo in blood or cerebrospinal fluid reflected the metabolic adaptation to these host niches with different nutrient availability; however, similar key metabolic activities were identified under these conditions. This points at the robustness of the core metabolic pathways in S. suis during the infection process. The crucial role of PEP carboxylation for growth of S. suis in the host was supported by experiments with a PEP carboxylase-deficient mutant strain in blood and cerebrospinal fluid.