New Insights into the Structure and Assembly of Bacteriophage P1.

Bacteriophage P1 is the premier transducing phage of E. coli. Despite its prominence in advancing E. coli genetics, modern molecular techniques have not been applied to thoroughly understand P1 structure. Here, we report the proteome of the P1 virion as determined by liquid chromatography tandem mass-spectrometry. Additionally, a library of single-gene knockouts identified the following five previously unknown essential genes: pmgA, pmgB, pmgC, pmgG, and pmgR. In addition, proteolytic processing of the major capsid protein is a known feature of P1 morphogenesis, and we identified the processing site by N-terminal sequencing to be between E120 and S121, producing a 448-residue, 49.3 kDa mature peptide. Furthermore, the P1 defense against restriction (Dar) system consists of six known proteins that are incorporated into the virion during morphogenesis. The largest of these, DarB, is a 250 kDa protein that is believed to translocate into the cell during infection. DarB deletions indicated the presence of an N-terminal packaging signal, and the N-terminal 30 residues of DarB are shown to be sufficient for directing a heterologous reporter protein to the capsid. Taken together, the data expand on essential structural P1 proteins as well as introduces P1 as a nanomachine for cellular delivery.

Genome-wide screens reveal Escherichia coli genes required for growth of T1-like phage LL5 and V5-like phage LL12.

The host factor requirements of phages and mechanisms of mutational phage insensitivity must be characterized for rational design of phage cocktails. To characterize host dependencies of two novel Escherichia coli phages, the T1-like siphophage LL5 and the V5-like myophage LL12, forward genetic screens were conducted against the Keio collection, a library of single non-essential gene deletions in E. coli str. BW25113. These screens and subsequent experiments identified genes required by phages LL5 and LL12. E. coli mutants deficient in heptose II and the phosphoryl substituent of heptose I of the inner core lipopolysaccharide (LPS) were unable to propagate phage LL5, as were mutants deficient in the outer membrane protein TolC. Mutants lacking glucose I of the LPS outer core failed to propagate LL12. Two additional genes encoding cytoplasmic chaperones, PpiB and SecB, were found to be required for efficient propagation of phage LL5, but not LL12. This screening approach may be useful for identifying host factors dependencies of phages, which would provide valuable information for their potential use as therapeutics and for phage engineering.

Biomimetic nanovesicles made from iPS cell-derived mesenchymal stem cells for targeted therapy of triple-negative breast cancer.

Nanoparticles made from membrane of mesenchymal stem cells (MSCs) showed active targeting capacities to prostate and lung cancers, but further studies are hindered by limited expandability and donor variations of tissue-derived MSCs. We have derived MSCs with an unlimited supply and uniform homing capacity to triple-negative breast cancer (TNBC) from human induced pluripotent stem cells (iPSCs). By breaking down intact iPSC-MSCs, we efficiently developed nanovesicles that selectively accumulated in primary and metastatic TNBC after systemic infusion in mouse models. When loaded with a chemotherapeutic drug doxorubicin, iPSC-MSC nanovesicles showed superior cytotoxic effects on doxorubicin-resistant TNBC cells, and significantly decreased the incidence and burden of metastases in mouse models of spontaneous and experimental metastatic TNBC compared with free or liposomal doxorubicin. These nanovesicles showed no detectable immunogenicity or toxicity, and are stable after storage. Our data indicate that iPSC-MSC nanovesicles are promising to improve TNBC treatment as a standardized targeting platform.

Complete Genome Sequence of Serratia marcescens Siphophage Scapp.

Serratia marcescens is an opportunistic pathogen that typically infects the respiratory and urinary tract, with the majority of cases being hospital acquired. The study of S. marcescens phages may help control drug-resistant S. marcescens strains. In this study, we announce the complete genome sequence and the features of S. marcescens siphophage Scapp.