SciCombinator

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Journal: Nature microbiology

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Despite the wide availability of antibiotics, infectious diseases remain a leading cause of death worldwide 1 . In the absence of new therapies, mortality rates due to untreatable infections are predicted to rise more than tenfold by 2050. Natural products (NPs) made by cultured bacteria have been a major source of clinically useful antibiotics. In spite of decades of productivity, the use of bacteria in the search for new antibiotics was largely abandoned due to high rediscovery rates2,3. As only a fraction of bacterial diversity is regularly cultivated in the laboratory and just a fraction of the chemistries encoded by cultured bacteria are detected in fermentation experiments, most bacterial NPs remain hidden in the global microbiome. In an effort to access these hidden NPs, we have developed a culture-independent NP discovery platform that involves sequencing, bioinformatic analysis and heterologous expression of biosynthetic gene clusters captured on DNA extracted from environmental samples. Here, we describe the application of this platform to the discovery of the malacidins, a distinctive class of antibiotics that are commonly encoded in soil microbiomes but have never been reported in culture-based NP discovery efforts. The malacidins are active against multidrug-resistant pathogens, sterilize methicillin-resistant Staphylococcus aureus skin infections in an animal wound model and did not select for resistance under our laboratory conditions.

Concepts: DNA, Infectious disease, Bacteria, Microbiology, Pneumonia, Staphylococcus aureus, Infection, Antibiotic resistance

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Natural transformation is a broadly conserved mechanism of horizontal gene transfer in bacterial species that can shape evolution and foster the spread of antibiotic resistance determinants, promote antigenic variation and lead to the acquisition of novel virulence factors. Surface appendages called competence pili promote DNA uptake during the first step of natural transformation 1 ; however, their mechanism of action has remained unclear owing to an absence of methods to visualize these structures in live cells. Here, using the model naturally transformable species Vibrio cholerae and a pilus-labelling method, we define the mechanism for type IV competence pilus-mediated DNA uptake during natural transformation. First, we show that type IV competence pili bind to extracellular double-stranded DNA via their tip and demonstrate that this binding is critical for DNA uptake. Next, we show that type IV competence pili are dynamic structures and that pilus retraction brings tip-bound DNA to the cell surface. Finally, we show that pilus retraction is spatiotemporally coupled to DNA internalization and that sterically obstructing pilus retraction prevents DNA uptake. Together, these results indicate that type IV competence pili directly bind to DNA via their tip and mediate DNA internalization through retraction during this conserved mechanism of horizontal gene transfer.

37

With the recent emergence of reports on resistant Gram-negative ‘superbugs’, infections caused by multidrug-resistant (MDR) Gram-negative bacteria have been named as one of the most urgent global health threats due to the lack of effective and biocompatible drugs. Here, we show that a class of antimicrobial agents, termed ‘structurally nanoengineered antimicrobial peptide polymers’ (SNAPPs) exhibit sub-μM activity against all Gram-negative bacteria tested, including ESKAPE and colistin-resistant and MDR (CMDR) pathogens, while demonstrating low toxicity. SNAPPs are highly effective in combating CMDR Acinetobacter baumannii infections in vivo, the first example of a synthetic antimicrobial polymer with CMDR Gram-negative pathogen efficacy. Furthermore, we did not observe any resistance acquisition by A. baumannii (including the CMDR strain) to SNAPPs. Comprehensive analyses using a range of microscopy and (bio)assay techniques revealed that the antimicrobial activity of SNAPPs proceeds via a multimodal mechanism of bacterial cell death by outer membrane destabilization, unregulated ion movement across the cytoplasmic membrane and induction of the apoptotic-like death pathway, possibly accounting for why we did not observe resistance to SNAPPs in CMDR bacteria. Overall, SNAPPs show great promise as low-cost and effective antimicrobial agents and may represent a weapon in combating the growing threat of MDR Gram-negative bacteria.

Concepts: Immune system, Protein, Cell, Bacteria, Microbiology, Antibiotic resistance, Gram-negative bacteria, Acinetobacter baumannii

29

Although genetically compact, HIV-1 commandeers vast arrays of cellular machinery to sustain and protect it during cycles of viral outgrowth. Transposon-mediated saturation linker scanning mutagenesis was used to isolate fully replication-competent viruses harbouring a potent foreign epitope tag. Using these viral isolates, we performed differential isotopic labelling and affinity-capture mass spectrometric analyses on samples obtained from cultures of human lymphocytes to classify the vicinal interactomes of the viral Env and Vif proteins as they occur during natural infection. Importantly, interacting proteins were recovered without bias, regardless of their potential for positive, negative or neutral impact on viral replication. We identified specific host associations made with trimerized Env during its biosynthesis, at virological synapses, with innate immune effectors (such as HLA-E) and with certain cellular signalling pathways (for example, Notch1). We also defined Vif associations with host proteins involved in the control of nuclear transcription and nucleoside biosynthesis as well as those interacting stably or transiently with the cytoplasmic protein degradation apparatus. Our approach is broadly applicable to elucidating pathogen-host interactomes, providing high-certainty identification of interactors by their direct access during cycling infection. Understanding the pathophysiological consequences of these associations is likely to provide strategic targets for antiviral intervention.

Concepts: Immune system, Antibody, DNA, Protein, Gene, Cell nucleus, Signal transduction, Virus

28

Antibiotic exposure in children has been associated with the risk of inflammatory bowel disease (IBD). Antibiotic use in children or in their pregnant mother can affect how the intestinal microbiome develops, so we asked whether the transfer of an antibiotic-perturbed microbiota from mothers to their children could affect their risk of developing IBD. Here we demonstrate that germ-free adult pregnant mice inoculated with a gut microbial community shaped by antibiotic exposure transmitted their perturbed microbiota to their offspring with high fidelity. Without any direct or continued exposure to antibiotics, this dysbiotic microbiota in the offspring remained distinct from controls for at least 21 weeks. By using both IL-10-deficient and wild-type mothers, we showed that both inoculum and genotype shape microbiota populations in the offspring. Because IL10-/- mice are genetically susceptible to colitis, we could assess the risk due to maternal transmission of an antibiotic-perturbed microbiota. We found that the IL10-/- offspring that had received the perturbed gut microbiota developed markedly increased colitis. Taken together, our findings indicate that antibiotic exposure shaping the maternal gut microbiota has effects that extend to the offspring, with both ecological and long-term disease consequences.

Concepts: Inflammation, Gene, Bacteria, Ulcerative colitis, Gastroenterology, Inflammatory bowel disease, Antibiotic, Mother

28

Blood CD14(+) monocytes are frontline immunomodulators categorized into classical, intermediate or non-classical subsets, and subsequently differentiated into M1 pro- or M2 anti-inflammatory macrophages on stimulation. Although the Zika virus (ZIKV) rapidly establishes viraemia, the target cells and immune responses, particularly during pregnancy, remain elusive. Furthermore, it is unknown whether African- and Asian-lineage ZIKV have different phenotypic impacts on host immune responses. Using human blood infection, we identified CD14(+) monocytes as the primary target for African- or Asian-lineage ZIKV infection. When immunoprofiles of human blood infected with ZIKV were compared, a classical/intermediate monocyte-mediated M1-skewed inflammation by the African-lineage ZIKV infection was observed, in contrast to a non-classical monocyte-mediated M2-skewed immunosuppression by the Asian-lineage ZIKV infection. Importantly, infection of the blood of pregnant women revealed an enhanced susceptibility to ZIKV infection. Specifically, Asian-lineage ZIKV infection of pregnant women’s blood led to an exacerbated M2-skewed immunosuppression of non-classical monocytes in conjunction with a global suppression of type I interferon-signalling pathway and an aberrant expression of host genes associated with pregnancy complications. Also, 30 ZIKV(+) sera from symptomatic pregnant patients showed elevated levels of M2-skewed immunosuppressive cytokines and pregnancy-complication-associated fibronectin-1. This study demonstrates the differential immunomodulatory responses of blood monocytes, particularly during pregnancy, on infection with different lineages of ZIKV.Both African and epidemic strains of Zika virus are shown to target CD14(+) monocytes, which are more susceptible in pregnant women, but African strains are associated with inflammatory responses, and epidemic strains with immunotolerance.

Concepts: Immune system, Inflammation, White blood cell, Gene, Pregnancy, Childbirth, Fetus, Immunology

24

Bacterial cell-cell signalling, or quorum sensing, is characterized by the secretion and groupwide detection of small diffusible signal molecules called autoinducers. This mechanism allows cells to coordinate their behaviour in a density-dependent manner. A quorum-sensing cell may directly respond to the autoinducers it produces in a cell-autonomous and quorum-independent manner, but the strength of this self-sensing effect and its impact on bacterial physiology are unclear. Here, we explore the existence and impact of self-sensing in the Bacillus subtilis ComQXP and Rap-Phr quorum-sensing systems. By comparing the quorum-sensing response of autoinducer-secreting and non-secreting cells in co-culture, we find that secreting cells consistently show a stronger response than non-secreting cells. Combining genetic and quantitative analyses, we demonstrate this effect to be a direct result of self-sensing and rule out an indirect regulatory effect of the autoinducer production genes on response sensitivity. In addition, self-sensing in the ComQXP system affects persistence to antibiotic treatment. Together, these findings indicate the existence of self-sensing in the two most common designs of quorum-sensing systems of Gram-positive bacteria. Bacillus subtilis cells are able to sense self-produced autoinducers, which gives rise to stronger quorum-sensing-mediated responses, in a process that can influence the generation of persisters during antibiotic treatment.

Concepts: DNA, Genetics, Cell, Bacteria, Microbiology, Bacillus, Quorum sensing, Bacillus subtilis

24

Challenges in cultivating microorganisms have limited the phylogenetic diversity of currently available microbial genomes. This is being addressed by advances in sequencing throughput and computational techniques that allow for the cultivation-independent recovery of genomes from metagenomes. Here, we report the reconstruction of 7,903 bacterial and archaeal genomes from >1,500 public metagenomes. All genomes are estimated to be ≥50% complete and nearly half are ≥90% complete with ≤5% contamination. These genomes increase the phylogenetic diversity of bacterial and archaeal genome trees by >30% and provide the first representatives of 17 bacterial and three archaeal candidate phyla. We also recovered 245 genomes from the Patescibacteria superphylum (also known as the Candidate Phyla Radiation) and find that the relative diversity of this group varies substantially with different protein marker sets. The scale and quality of this data set demonstrate that recovering genomes from metagenomes provides an expedient path forward to exploring microbial dark matter.The recovery of 7,903 bacterial and archaeal metagenome-assembled genomes increases the phylogenetic diversity represented by public genome repositories and provides the first representatives from 20 candidate phyla.

Concepts: Gene, Archaea, Bacteria, Organism, Genome, Horizontal gene transfer, Biotechnology, Microorganism

24

The temporal dynamics of phytoplankton growth and activity have large impacts on fluxes of matter and energy, yet obtaining in situ metabolic measurements of sufficient resolution for even dominant microorganisms remains a considerable challenge. We performed Lagrangian diel sampling with synoptic measurements of population abundances, dinitrogen (N2) fixation, mortality, productivity, export and transcription in a bloom of Crocosphaera over eight days in the North Pacific Subtropical Gyre (NPSG). Quantitative transcriptomic analyses revealed clear diel oscillations in transcript abundances for 34% of Crocosphaera genes identified, reflecting a systematic progression of gene expression in diverse metabolic pathways. Significant time-lagged correspondence was evident between nifH transcript abundance and maximal N2 fixation, as well as sepF transcript abundance and cell division, demonstrating the utility of transcriptomics to predict the occurrence and timing of physiological and biogeochemical processes in natural populations. Indirect estimates of carbon fixation by Crocosphaera were equivalent to 11% of net community production, suggesting that under bloom conditions this diazotroph has a considerable impact on the wider carbon cycle. Our cross-scale synthesis of molecular, population and community-wide data underscores the tightly coordinated in situ metabolism of the keystone N2-fixing cyanobacterium Crocosphaera, as well as the broader ecosystem-wide implications of its activities.

Concepts: DNA, Gene, Carbon dioxide, Gene expression, Bacteria, Metabolism, Organism, Nitrogen

24

Many bacteria, including Legionella pneumophila, rely on the type IV secretion system to translocate a repertoire of effector proteins into the hosts for their survival and growth. Type IV coupling protein (T4CP) is a hexameric ATPase that links translocating substrates to the transenvelope secretion conduit. Yet, how a large number of effector proteins are selectively recruited and processed by T4CPs remains enigmatic. DotL, the T4CP of L. pneumophila, contains an ATPase domain and a C-terminal extension whose function is unknown. Unlike T4CPs involved in plasmid DNA translocation, DotL appeared to function by forming a multiprotein complex with four other proteins. Here, we show that the C-terminal extension of DotL interacts with DotN, IcmS, IcmW and an additionally identified subunit LvgA, and that this pentameric assembly binds Legionella effector proteins. We determined the crystal structure of this assembly and built an architecture of the T4CP holocomplex by combining a homology model of the ATPase domain of DotL. The holocomplex is a hexamer of a bipartite structure composed of a membrane-proximal ATPase domain and a membrane-distal substrate-recognition assembly. The presented information demonstrates the architecture and functional dissection of the multiprotein T4CP complexes and provides important insights into their substrate recruitment and processing.

Concepts: DNA, Protein, Protein structure, Cell, Enzyme, Function, Secretion, Category theory