Marcos Pires

Control and manipulation of bacterial populations requires an understanding of the factors that govern growth, division, and antibiotic action. Fluorescent and chemically reactive small molecule probes of cell envelope components can visualize these processes and advance our knowledge of cell envelope biosynthesis (e.g., peptidoglycan production). Still, fundamental gaps remain in...

Simm et al. demonstrate a computational method to predict the activities of compounds in hundreds of biological assays from a single image-based screen of half a million compounds. The resulting models boosted the identification and diversity of hit compounds for two projects, encouraging further research in this field.

Shimada et al. report that the compound NSC319726 arrests glioblastoma-patient-derived cells at picomolar concentrations. The compound binds to copper, generates ROS using ambient oxygen, and depletes nucleotide pools. This represents a new strategy for potently blocking the growth of glioblastoma.

Optically-controlled bacterial metabolite for cancer therapy

Optically-controlled bacterial metabolite for cancer therapy, Published online: 26 April 2018; doi:10.1038/s41467-018-03233-9

Targeting tumors with bacteria as vehicles for metabolite therapy suffers from low efficiency and robustness. Here, the authors combine carbon nitride with nitric oxide generation enzyme-positive E. coli for photo-controlled metabolite therapy (PMT) and observe increased effects both in vitro and in tumor-bearing mice.

The missing live-cell evidence proving the fusion pore hypothesis reveals metastable pores that are two orders of magnitude larger than previously thought and can constrict and close instantly or slowly.

Staphylococcus aureus blocks insulin function

<i>Staphylococcus aureus</i> blocks insulin function, Published online: 24 April 2018; doi:10.1038/s41564-018-0153-3

The bacterial pathogen Staphylococcus aureus secretes a high-affinity insulin-binding protein that mediates insulin resistance, a major driver of obesity and type 2 diabetes, in a mouse model of infection.

ChemBioChem, Volume 19, Issue 9, Page 891-891, May 4, 2018.

by Akshay Sabnis, Elizabeth V. K. Ledger, Vera Pader, Andrew M. Edwards

Self-replication of DNA by its encoded proteins in liposome-based synthetic cells

Self-replication of DNA by its encoded proteins in liposome-based synthetic cells, Published online: 20 April 2018; doi:10.1038/s41467-018-03926-1

Replicating DNA and converting genetic information to protein is a feature of cellular life. Here the authors implement a coupled DNA replication and gene expression system inside vesicles.

Combination of single-cell DNA and RNA sequencing depicts the evolutionary trajectories of chemoresistance in human triple-negative breast cancer at the genomic and transcriptomic level, highlighting the presence of pre-existing genomic alterations and transcriptional reprogramming of resistant signatures.

The extracellular domain of Staphylococcus aureus LtaS binds insulin and induces insulin resistance during infection

The extracellular domain of <i>Staphylococcus aureus</i> LtaS binds insulin and induces insulin resistance during infection, Published online: 16 April 2018; doi:10.1038/s41564-018-0146-2

The extracellular domain of the cell wall protein LtaS is an insulin-binding protein and mediates insulin resistance during Staphylococcus aureus infection.

Angewandte Chemie International Edition, EarlyView.

Angewandte Chemie International Edition, EarlyView.

Genome-wide mutant profiling predicts the mechanism of a Lipid II binding antibiotic

Genome-wide mutant profiling predicts the mechanism of a Lipid II binding antibiotic, Published online: 16 April 2018; doi:10.1038/s41589-018-0041-4

Use of a combined Tn-seq and machine-learning approach for predicting mechanisms and targets of antibiotic action in Staphylococcus aureus shows that the natural product lysocin E (LysE) binds Lipid II on the cell surface and damages the membrane.

We present two CRISPR-mediated analog multi-event recording apparatus (CAMERA) systems that use base editors and Cas9 nucleases to record cellular events in bacteria and mammalian cells. The devices record signal amplitude or duration as changes in the ratio of mutually exclusive DNA sequences (CAMERA 1) or as single-base modifications (CAMERA 2). We achieved recording of multiple stimuli in bacteria or mammalian cells, including exposure to antibiotics, nutrients, viruses, light, and changes in Wnt signaling. When recording to multicopy plasmids, reliable readout requires as few as 10 to 100 cells. The order of stimuli can be recorded through an overlapping guide RNA design, and memories can be erased and re-recorded over multiple cycles. CAMERA systems serve as "cell data recorders" that write a history of endogenous or exogenous signaling events into permanent DNA sequence modifications in living cells.

Release of Staphylococcus aureus extracellular vesicles and their application as a vaccine platform

Release of <i>Staphylococcus aureus</i> extracellular vesicles and their application as a vaccine platform, Published online: 11 April 2018; doi:10.1038/s41467-018-03847-z

Extracellular vesicles (EVs) influence host-pathogen interactions, but EV biogenesis in gram-positive bacteria remains elusive. Here authors characterize EVs from Staphylococcus aureus and show that phenol-soluble modulins and autolysins promote EV biogenesis by disrupting the membrane and cell wall.

ABSTRACT

Gram-positive bacteria, including the major respiratory pathogen Streptococcus pneumoniae, were recently shown to produce extracellular vesicles (EVs) that likely originate from the plasma membrane and are released into the extracellular environment. EVs may function as cargo for many bacterial proteins, however, their involvement in cellular processes and their interactions with the innate immune system are poorly understood. Here, EVs from pneumococci were characterized and their immunomodulatory effects investigated. Pneumococcal EVs were protruding from the bacterial surface and released into the medium as 25 to 250 nm lipid stained vesicles containing a large number of cytosolic, membrane, and surface-associated proteins. The cytosolic pore-forming toxin pneumolysin was significantly enriched in EVs compared to a total bacterial lysate but was not required for EV formation. Pneumococcal EVs were internalized into A549 lung epithelial cells and human monocyte-derived dendritic cells and induced proinflammatory cytokine responses irrespective of pneumolysin content. EVs from encapsulated pneumococci were recognized by serum proteins, resulting in C3b deposition and formation of C5b-9 membrane attack complexes as well as factor H recruitment, depending on the presence of the choline binding protein PspC. Addition of EVs to human serum decreased opsonophagocytic killing of encapsulated pneumococci. Our data suggest that EVs may act in an immunomodulatory manner by allowing delivery of vesicle-associated proteins and other macromolecules into host cells. In addition, EVs expose targets for complement factors in serum, promoting pneumococcal evasion of humoral host defense.

IMPORTANCE Streptococcus pneumoniae is a major contributor to morbidity and mortality worldwide, being the major cause of milder respiratory tract infections such as otitis and sinusitis and of severe infections such as community-acquired pneumonia, with or without septicemia, and meningitis. More knowledge is needed on how pneumococci interact with the host, deliver virulence factors, and activate immune defenses. Here we show that pneumococci form extracellular vesicles that emanate from the plasma membrane and contain virulence properties, including enrichment of pneumolysin. We found that pneumococcal vesicles can be internalized into epithelial and dendritic cells and bind complement proteins, thereby promoting pneumococcal evasion of complement-mediated opsonophagocytosis. They also induce pneumolysin-independent proinflammatory responses. We suggest that these vesicles can function as a mechanism for delivery of pneumococcal proteins and other immunomodulatory components into host cells and help pneumococci to avoid complement deposition and phagocytosis-mediated killing, thereby possibly contributing to the symptoms found in pneumococcal infections.

A technology to prime desired populations of T cells in the body—particularly those that possess low avidity against target antigen—would pave the way for the design of new types of vaccination for intractable infectious diseases or cancer. Here, we report such a technology based on positive feedback-driven, programmed self-assembly of...

ABSTRACT

Enterococcus faecalis strains resistant to penicillin and ampicillin are rare and have been associated with increases in quantities of low-affinity penicillin-binding protein 4 (PBP4) or with amino acid substitutions in PBP4. We report an E. faecalis strain (LS4828) isolated from a prosthetic knee joint that was subjected to long-term exposure to aminopenicillins. Subsequent cultures yielded E. faecalis with MICs of penicillins and carbapenems higher than those for wild-type strain E. faecalis JH2-2. Sequence analysis of the pbp4 gene of LS4828 compared to that of JH2-2 revealed two point mutations with amino acid substitutions (V223I, A617T) and deletion of an adenine from the region upstream of the predicted pbp4 –35 promoter sequence (UP region). Purified PBP4 from LS4828 exhibited less affinity for Bocillin FL than did PBP4 from JH2-2, which was recapitulated by purified PBP4 containing only the A617T mutation. Differential scanning fluorimetry studies showed that the LS4828 and A617T variants are destabilized compared to wild-type PBP4. Further, reverse transcription-PCR indicated increased transcription of pbp4 in LS4828 and Western blot analysis with polyclonal PBP4 antibody revealed greater quantities of PBP4 in LS4828 than in JH2-2 lysates and membrane preparations. Placing the promoter regions from LS4828 or JH2-2 upstream of a green fluorescent protein reporter gene confirmed that the adenine deletion was associated with increased transcription. Together, these data suggest that the reduced susceptibility to β-lactam antibiotics observed in E. faecalis LS4828 results from a combination of both increased expression and remodeling of the active site, resulting in reduced affinity for penicillins and carbapenems.

IMPORTANCE Enterococcus faecalis is an important cause of community-acquired and nosocomial infections and creates therapeutic dilemmas because of its frequent resistance to several classes of antibiotics. We report an E. faecalis strain with decreased ampicillin and imipenem susceptibility isolated after prolonged courses of aminopenicillin therapy for a prosthetic joint infection. Its reduced susceptibility is attributable to a combination of increased quantities of low-affinity PBP4 and an amino acid substitution in proximity to the active site that destabilizes the protein. Our findings provide a cautionary tale for clinicians who elect to "suppress" infections in prosthetic joints and offer novel insights into the interaction of β-lactam antibiotics with low-affinity PBP4. These insights will help inform future efforts to develop therapeutics capable of inhibiting clinical enterococcal strains.

ABSTRACT

Peptidoglycan is a sugar/amino acid polymer unique to bacteria and essential for division and cell shape maintenance. The d-amino acids that make up its cross-linked stem peptides are not abundant in nature and must be synthesized by bacteria de novo. d-Glutamate is present at the second position of the pentapeptide stem and is strictly conserved in all bacterial species. In Gram-negative bacteria, d-glutamate is generated via the racemization of l-glutamate by glutamate racemase (MurI). Chlamydia trachomatis is the leading cause of infectious blindness and sexually transmitted bacterial infections worldwide. While its genome encodes a majority of the enzymes involved in peptidoglycan synthesis, no murI homologue has ever been annotated. Recent studies have revealed the presence of peptidoglycan in C. trachomatis and confirmed that its pentapeptide includes d-glutamate. In this study, we show that C. trachomatis synthesizes d-glutamate by utilizing a novel, bifunctional homologue of diaminopimelate epimerase (DapF). DapF catalyzes the final step in the synthesis of meso-diaminopimelate, another amino acid unique to peptidoglycan. Genetic complementation of an Escherichia coli murI mutant demonstrated that Chlamydia DapF can generate d-glutamate. Biochemical analysis showed robust activity, but unlike canonical glutamate racemases, activity was dependent on the cofactor pyridoxal phosphate. Genetic complementation, enzymatic characterization, and bioinformatic analyses indicate that chlamydial DapF shares characteristics with other promiscuous/primordial enzymes, presenting a potential mechanism for d-glutamate synthesis not only in Chlamydia but also numerous other genera within the Planctomycetes-Verrucomicrobiae-Chlamydiae superphylum that lack recognized glutamate racemases.

IMPORTANCE Here we describe one of the last remaining "missing" steps in peptidoglycan synthesis in pathogenic Chlamydia species, the synthesis of d-glutamate. We have determined that the diaminopimelate epimerase (DapF) encoded by Chlamydia trachomatis is capable of carrying out both the epimerization of DAP and the pyridoxal phosphate-dependent racemization of glutamate. Enzyme promiscuity is thought to be the hallmark of early microbial life on this planet, and there is currently an active debate as to whether "moonlighting enzymes" represent primordial evolutionary relics or are a product of more recent reductionist evolutionary pressures. Given the large number of Chlamydia species (as well as members of the Planctomycetes-Verrucomicrobiae-Chlamydiae superphylum) that possess DapF but lack homologues of MurI, it is likely that DapF is a primordial isomerase that functions as both racemase and epimerase in these organisms, suggesting that specialized d-glutamate racemase enzymes never evolved in these microbes.

ChemBioChem, Volume 19, Issue 9, Page 931-939, May 4, 2018.

The dTAG system for immediate and target-specific protein degradation

The dTAG system for immediate and target-specific protein degradation, Published online: 26 March 2018; doi:10.1038/s41589-018-0021-8

The dTAG system pairs potent heterobifunctional degraders and extensible tagging strategies to achieve immediate and reversible degradation of divergent proteins, facilitating biological investigation and drug target validation in cells and in mice.

Thackray et al. observed increased susceptibility to West Nile, Zika, and Dengue virus infections following oral antibiotic treatment in mice. Antibiotics altered the bacterial abundance and community structure and the development of optimal T cell immunity. These data suggest that antibiotics may have deleterious consequences for subsequent flavivirus infections.

Bipartite expression systems, such as the GAL4-UAS system, allow fine manipulation of gene expression and are powerful tools for interrogating gene function. Recently, we established cGAL, a GAL4-based bipartite expression system for transgene control in Caenorhabditis elegans, where a single promoter dictates the expression pattern of a cGAL driver, which...