Project description:Bacteriophages (phages) are widespread in Streptococcus pneumoniae, with most strains carrying phage genomes integrated into the chromosome. RNA sequencing was utilised to explore whether phage gene expression could be detected. The pneumococcal reference strain PMEN3 (Spain9V-3), which contained two full-length phages and one partial phage, was grown in broth culture and mitomycin C was added to facilitate phage induction. PMEN3 culture samples were taken at sequential time points and RNA was extracted and sequenced.
Project description:Whole-genome sequencing is an important way to understand the genetic information, gene function, biological characteristics, and living mechanisms of organisms. There is no difficulty to have mega-level genomes sequenced at present. However, we encountered a hard-to-sequence genome of Pseudomonas aeruginosa phage PaP1. The shotgun sequencing method failed to dissect this genome. After insisting for 10 years and going over 3 generations of sequencing techniques, we successfully dissected the PaP1 genome with 91,715 bp in length. Single-molecule sequencing revealed that this genome contains lots of modified bases, including 51 N6-methyladenines (m6A) and 152 N4-methylcytosines (m4C). At the same time, further investigations revealed a novel immune mechanism of bacteria, by which the host bacteria can recognize and repel the modified bases containing inserts in large scale, and this led to the failure of the shotgun method in PaP1 genome sequencing. Strategy of resolving this problem is use of non-library dependent sequencing techniques or use of the nfi- mutant of E. coli DH5M-NM-1 as the host bacteria to construct the shotgun library. In conclusion, we unlock the mystery of phage PaP1 genome hard to be sequenced, and discover a new mechanism of bacterial immunity in present study. Methylation profiling of Pseudomonas aeruginosa phage PaP1 using kinetic data generated by single-molecule, real-time (SMRT) sequencing on the PacBio RS.
Project description:Phage-like elements are found in a multitude of streptococcal species, including pneumococcal strain Hungary19A-6 (SpnCI). The aim of our research was to investigate the role of phage-like element SpnCI in enhanced virulence and phenotypic modulation within Streptococcus pneumoniae. SpnCI was found to significantly enhance virulence within the invertebrate infection model Galleria mellonella. Infections with SpnCI led to a lower mean health score (1.6) and survival percentage (20%) compared to SpnCI null TIGR4 infections (3.85 mean health score and 50% survival). SpnCI remained integrated throughout growth, conferring greater sensitivity to UV irradiation. Change in transcriptional patterns occurred, including downregulation of operons involved with cell surface modelling in the SpnCI containing strain of TIGR4. Kanamycin-tagged SpnCI strain in Hungary19A-6 was inducible and isolated from lysate along with both annotated prophages. No phages were identified by PCR nor electron microscopy (EM) following induction of TIGR4 SpnCI∆strA suggesting helper-phage dependence for dissemination. EM of lysate showed typical siphoviridae morphology with an average capsid size of 60 nm. Two of sixty capsids were found to be smaller, suggesting SpnCI disseminates using a similar mechanism described for Staphylococcus aureus phage-like element SaPI. SpnCI from lysate infected capsule null strain T4R but was incapable of infecting the encapsulated TIGR4 strain suggesting that capsule impedes phage infection. Our work demonstrates that SpnCI can modulate virulence, UV susceptibility, alter transcriptional patterns, and furthermore, can disseminate via infection within pneumococcus. Further research is necessary to elucidate how SpnCI modulates virulence and what genes are responsible for the enhanced virulence phenotype.
Project description:Viral genomes are most vulnerable to cellular defenses at the start of the infection. A family of jumbo phages related to phage ΦKZ, which infects Pseudomonas aeruginosa, assembles a protein-based phage nucleus to protect replicating phage DNA, but how it is protected prior to phage nucleus assembly is unclear. We find that host proteins related to membrane and lipid biology interact with injected phage protein, clustering in an early phage infection (EPI) vesicle. The injected virion RNA polymerase (vRNAP) executes early gene expression until phage genome separation from the vRNAP and the EPI vesicle, moving into the nascent proteinaceous phage nucleus. Enzymes involved in DNA replication and CRISPR/restriction immune nucleases are excluded by the EPI vesicle. We propose that the EPI vesicle is rapidly constructed with injected phage proteins, phage DNA, host lipids, and host membrane proteins to enable genome protection, early transcription, localized translation, and to ensure faithful genome transfer to the proteinaceous nucleus.