Renaissance for Phage-Based Bacterial Control.

Bacteriophages (phages) are an underutilized biological resource with vast potential for pathogen control and microbiome editing. Phage research and commercialization have increased rapidly in biomedical and agricultural industries, but adoption has been limited elsewhere. Nevertheless, converging advances in DNA sequencing, bioinformatics, microbial ecology, and synthetic biology are now poised to broaden phage applications beyond pathogen control toward the manipulation of microbial communities for defined functional improvements. Enhancements in sequencing combined with network analysis make it now feasible to identify and disrupt microbial associations to elicit desirable shifts in community structure or function, indirectly modulate species abundance, and target hub or keystone species to achieve broad functional shifts. Sequencing and bioinformatic advancements are also facilitating the use of temperate phages for safe gene delivery applications. Finally, integration of synthetic biology stands to create novel phage chassis and modular genetic components. While some fundamental, regulatory, and commercialization barriers to widespread phage use remain, many major challenges that have impeded the field now have workable solutions. Thus, a new dawn for phage-based (chemical-free) precise biocontrol and microbiome editing is on the horizon to enhance, suppress, or modulate microbial activities important for public health, food security, and more sustainable energy production and water reuse.

Formate cross-feeding and cooperative metabolic interactions revealed by transcriptomics in co-cultures of acetogenic and amylolytic human colonic bacteria.

Interspecies cross-feeding is a fundamental factor in anaerobic microbial communities. In the human colon, formate is produced by many bacterial species but is normally detected only at low concentrations. Ruminococcus bromii produces formate, ethanol and acetate in approximately equal molar proportions in pure culture on RUM-RS medium with 0.2% Novelose resistant starch (RS3) as energy source. Batch co-culturing on starch with the acetogen Blautia hydrogenotrophica however led to the disappearance of formate and increased levels of acetate, which is proposed to occur through the routing of formate via the Wood Ljungdahl pathway of B. hydrogenotrophica. We investigated these inter-species interactions further using RNAseq to examine gene expression in continuous co-cultures of R. bromii and B. hydrogenotrophica. Transcriptome analysis revealed upregulation of B. hydrogenotrophica genes involved in the Wood-Ljungdahl pathway and of a 10 gene cluster responsible for increased branched chain amino acid fermentation in the co-cultures. Cross-feeding between formate-producing species and acetogens may be a significant factor in short chain fatty acid formation in the colon contributing to high rates of acetate production. Transcriptome analysis also indicated competition for the vitamin thiamine and downregulation of dissimilatory sulfate reduction and key redox proteins in R. bromii in the co-cultures, thus demonstrating the wide-ranging consequences of inter-species interactions in this model system.

PrgK, a multidomain peptidoglycan hydrolase, is essential for conjugative transfer of the pheromone-responsive plasmid pCF10.

Peptidoglycan (PG) hydrolases associated with bacterial type IV secretion systems (T4SSs) are thought to generate localized lesions in the PG layer to facilitate assembly of the translocation channel. The pheromone-responsive plasmid pCF10 of Enterococcus faecalis encodes a putative cell wall hydrolase, PrgK, and here we report that a prgK deletion abolished functionality of the pCF10-encoded T4SS as monitored by pCF10 conjugative transfer. Expression in trans of wild-type prgK fully complemented this mutation. PrgK has three potential hydrolase motifs resembling staphylococcal LytM, soluble lytic transglycosylase (SLT), and cysteine-, histidine-dependent amidohydrolase/peptidase (CHAP) domains. Complementation analyses with mutant alleles established that PrgK bearing two hydrolase domains in any combination supported near-wild-type plasmid transfer, and PrgK bearing a single hydrolase domain supported at least a low level of transfer in filter matings. When exported to the Escherichia coli periplasm, each domain disrupted cell growth, and combinations of domains additionally induced cell rounding and blebbing and conferred enhanced sensitivity to osmotic shock. Each domain bound PG in vitro, but only the SLT domain exhibited detectable hydrolase activity, as shown by zymographic analyses and release of fluorescent PG fragments. Genes encoding three T4SS-associated, putative hydrolases, Lactococcus lactis CsiA, Tn925 Orf14, and pIP501 TraG, partially complemented the ΔprgK mutation. Our findings establish that PrgK is an essential component of the pCF10-encoded Prg/Pcf T4SS and that its hydrolase domains coordinate their activities for full PrgK function. PrgK is indispensable for plasmid transfer in liquid matings, suggestive of a role in formation or stabilization of mating junctions.

A multiresistance megaplasmid pLG1 bearing a hylEfm genomic island in hospital Enterococcus faecium isolates.

Enterococcus faecium is considered to be a nosocomial pathogen with increasing medical importance. The putative virulence factor, hyl(Efm), encoding a putative hyaluronidase, is enriched among the hospital-associated polyclonal subpopulation of E. faecium.. The hyl(Efm) gene is described to be part of a genomic island and was recently identified to be plasmid-located. Here, we present a description of the structure, localization, and distribution of the putative pathogenicity factor hyl(Efm) and its putative island among 39 clinical isolates and elucidate the composition and host range of pLG1, a hyl(Efm) multiresistance plasmid of approximately 281.02kb. The hyl(Efm) gene was located within a 17,824-bp element highly similar to the putative genomic island (GI) structure that had been previously described. This genomic region was conserved among 39 hyl(Efm)-positive strains with variation in a specific region downstream of hyl(Efm) in 18 strains. The putative hyl(Efm) was located on large plasmids (150-350kb) in 37 strains. pLG1 could be horizontally transferred into four different E. faecium recipient strains (n=4) but not into E. faecalis (n=3). Sequencing of pLG1 resolved putative plasmid replication, conjugation, and maintenance determinants as well as a pilin gene cluster, carbon uptake and utilization genes, heavy metal and antibiotic resistance clusters. The hyl(Efm) transferable plasmid pLG1 bears additional putative pathogenicity factors and antibiotic resistance genes. These findings suggest horizontal gene transfer of virulence factors and antibiotic resistance gene clusters by a single genetic event (conjugative transfer) which might be triggered by heavy antibiotic use common in health care units where E. faecium is increasingly prevalent.

Global spread of the hyl(Efm) colonization-virulence gene in megaplasmids of the Enterococcus faecium CC17 polyclonal subcluster.

Enterococcus faecium has increasingly been reported as a nosocomial pathogen since the early 1990s, presumptively associated with the expansion of a human-associated Enterococcus faecium polyclonal subcluster known as clonal complex 17 (CC17) that has progressively acquired different antibiotic resistance (ampicillin and vancomycin) and virulence (esp(Efm), hyl(Efm), and fms) traits. We analyzed the presence and the location of a putative glycoside hydrolase hyl(Efm) gene among E. faecium strains obtained from hospitalized patients (255 patients; outbreak, bacteremic, and/or disseminated isolates from 23 countries and five continents; 1986 to 2009) and from nonclinical origins (isolates obtained from healthy humans [25 isolates], poultry [30], swine [90], and the environment [55]; 1999 to 2007). Clonal relatedness was established by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Plasmid analysis included determination of content and size (S1-PFGE), transferability (filter mating), screening of Rep initiator proteins (PCR), and location of vanA, vanB, ermB, and hyl(Efm) genes (S1/I-CeuI hybridization). Most E. faecium isolates contained large plasmids (>150 kb) and showed variable contents of van, hyl(Efm), or esp(Efm). The hyl(Efm) gene was associated with megaplasmids (170 to 375 kb) of worldwide spread (ST16, ST17, and ST18) or locally predominant (ST192, ST203, ST280, and ST412) ampicillin-resistant CC17 clones collected in the five continents since the early 1990s. All but one hyl(Efm)-positive isolate belonged to the CC17 polyclonal subcluster. The presence of hyl(Efm) megaplasmids among CC17 from Europe, Australia, Asia, and Africa since at least the mid-1990s was documented. This study further demonstrates the pandemic expansion of particular CC17 clones before acquisition of vancomycin resistance and putative virulence traits and describes the presence of megaplasmids in most of the contemporary E. faecium isolates with different origins.

Characterisation of multidrug-resistant Salmonella Typhimurium 4,[5],12:i:- DT193 strains carrying a novel genomic island adjacent to the thrW tRNA locus.

In 2006, monophasic, multidrug-resistant Salmonella enterica spp. enterica serovar 4,[5],12:i:- strains appeared as a novel serotype in Germany, associated with large diffuse outbreaks and increased need for hospitalisation. The emerging 4,[5],12:i:- strains isolated from patients in Germany belong mainly to phage type DT193 according to the Anderson phage typing scheme for S. Typhimurium (STM) and exhibit at least a tetra-drug resistance. The strains have been shown to harbour STM-specific Gifsy-1, Gifsy-2, and ST64B prophages. Furthermore, the extensive sequence similarity of the tRNA regions between one characterised 4,[5],12:i:- phage type DT193 and the S. Typhimurium LT2 strain as well as the STM-specific position of an IS200 element within the fliA-fliB intergenic region (Echeita et al., 2001) prompted us to classify them as a monophasic variant of S. Typhimurium. In 2008, the monophasic variant represented 42.2% of all S. Typhimurium isolates from human analysed at the National Reference Centre. Searching for insertions in tRNA sites resulted in the detection of an 18.4-kb fragment adjacent to the thrW tRNA locus, exhibiting a lower G+C content compared to the LT2 genome. Sequence analysis identified 17 potential ORFs. Some of them showed high similarity to enterobacterial phage sequences and sequences from Shigella boydii, Sh. dysenteriae, avian pathogenic Escherichia coli and other Escherichia spp. The biological function of this novel island with respect to virulence properties and metabolic functions is under investigation.

Mechanistic Insights Into the Cross-Feeding of Ruminococcus gnavus and Ruminococcus bromii on Host and Dietary Carbohydrates.

Dietary and host glycans shape the composition of the human gut microbiota with keystone carbohydrate-degrading species playing a critical role in maintaining the structure and function of gut microbial communities. Here, we focused on two major human gut symbionts, the mucin-degrader Ruminococcus gnavus ATCC 29149, and R. bromii L2-63, a keystone species for the degradation of resistant starch (RS) in human colon. Using anaerobic individual and co-cultures of R. bromii and R. gnavus grown on mucin or starch as sole carbon source, we showed that starch degradation by R. bromii supported the growth of R. gnavus whereas R. bromii did not benefit from mucin degradation by R. gnavus. Further we analyzed the growth (quantitative PCR), metabolite production (1H NMR analysis), and bacterial transcriptional response (RNA-Seq) of R. bromii cultured with RS or soluble starch (SS) in the presence or absence of R. gnavus. In co-culture fermentations on starch, 1H NMR analysis showed that R. gnavus benefits from transient glucose and malto-oligosaccharides released by R. bromii upon starch degradation, producing acetate, formate, and lactate as main fermentation end-products. Differential expression analysis (DESeq 2) on starch (SS and RS) showed that the presence of R. bromii induced changes in R. gnavus transcriptional response of genes encoding several maltose transporters and enzymes involved in its metabolism such as maltose phosphorylase, in line with the ability of R. gnavus to utilize R. bromii starch degradation products. In the RS co-culture, R. bromii showed a significant increase in the induction of tryptophan (Trp) biosynthesis genes and a decrease of vitamin B12 (VitB12)-dependent methionine biosynthesis as compared to the mono-culture, suggesting that Trp and VitB12 availability become limited in the presence of R. gnavus. Together this study showed a direct competition between R. bromii and R. gnavus on RS, suggesting that in vivo, the R. gnavus population inhabiting the mucus niche may be modulated by the supply of non-digestible carbohydrates reaching the colon such as RS.

Unique Organization of Extracellular Amylases into Amylosomes in the Resistant Starch-Utilizing Human Colonic Firmicutes Bacterium Ruminococcus bromii.

UNLABELLED: Ruminococcus bromii is a dominant member of the human gut microbiota that plays a key role in releasing energy from dietary starches that escape digestion by host enzymes via its exceptional activity against particulate "resistant" starches. Genomic analysis of R. bromii shows that it is highly specialized, with 15 of its 21 glycoside hydrolases belonging to one family (GH13). We found that amylase activity in R. bromii is expressed constitutively, with the activity seen during growth with fructose as an energy source being similar to that seen with starch as an energy source. Six GH13 amylases that carry signal peptides were detected by proteomic analysis in R. bromii cultures. Four of these enzymes are among 26 R. bromii proteins predicted to carry dockerin modules, with one, Amy4, also carrying a cohesin module. Since cohesin-dockerin interactions are known to mediate the formation of protein complexes in cellulolytic ruminococci, the binding interactions of four cohesins and 11 dockerins from R. bromii were investigated after overexpressing them as recombinant fusion proteins. Dockerins possessed by the enzymes Amy4 and Amy9 are predicted to bind a cohesin present in protein scaffoldin 2 (Sca2), which resembles the ScaE cell wall-anchoring protein of a cellulolytic relative, R. flavefaciens. Further complexes are predicted between the dockerin-carrying amylases Amy4, Amy9, Amy10, and Amy12 and two other cohesin-carrying proteins, while Amy4 has the ability to autoaggregate, as its dockerin can recognize its own cohesin. This organization of starch-degrading enzymes is unprecedented and provides the first example of cohesin-dockerin interactions being involved in an amylolytic system, which we refer to as an "amylosome." IMPORTANCE: Fermentation of dietary nondigestible carbohydrates by the human colonic microbiota supplies much of the energy that supports microbial growth in the intestine. This activity has important consequences for health via modulation of microbiota composition and the physiological and nutritional effects of microbial metabolites, including the supply of energy to the host from short-chain fatty acids. Recent evidence indicates that certain human colonic bacteria play keystone roles in degrading nondigestible substrates, with the dominant but little-studied species Ruminococcus bromii displaying an exceptional ability to degrade dietary resistant starches (i.e., dietary starches that escape digestion by host enzymes in the upper gastrointestinal tract because of protection provided by other polymers, particle structure, retrogradation, or chemical cross-linking). In this report, we reveal the unique organization of the amylolytic enzyme system of R. bromii that involves cohesin-dockerin interactions between component proteins. While dockerins and cohesins are fundamental to the organization of cellulosomal enzyme systems of cellulolytic ruminococci, their contribution to organization of amylases has not previously been recognized and may help to explain the starch-degrading abilities of R. bromii.

The expanding bacterial type IV secretion lexicon.

The bacterial type IV secretion systems (T4SSs) comprise a biologically diverse group of translocation systems functioning to deliver DNA or protein substrates from donor to target cells generally by a mechanism dependent on establishment of direct cell-to-cell contact. Members of one T4SS subfamily, the conjugation systems, mediate the widespread and rapid dissemination of antibiotic resistance and virulence traits among bacterial pathogens. Members of a second subfamily, the effector translocators, are used by often medically-important pathogens to deliver effector proteins to eukaryotic target cells during the course of infection. Here we summarize our current understanding of the structural and functional diversity of T4SSs and of the evolutionary processes shaping this diversity. We compare mechanistic and architectural features of T4SSs from Gram-negative and -positive species. Finally, we introduce the concept of the 'minimized' T4SSs; these are systems composed of a conserved set of 5-6 subunits that are distributed among many Gram-positive and some Gram-negative species.

Intra- and interspecies genomic transfer of the Enterococcus faecalis pathogenicity island.

Enterococci are the third leading cause of hospital associated infections and have gained increased importance due to their fast adaptation to the clinical environment by acquisition of antibiotic resistance and pathogenicity traits. Enterococcus faecalis harbours a pathogenicity island (PAI) of 153 kb containing several virulence factors including the enterococcal surface protein (esp). Until now only internal fragments of the PAI or larger chromosomal regions containing it have been transferred. Here we demonstrate precise excision, circularization and horizontal transfer of the entire PAI element from the chromosome of E. faecalis strain UW3114. This PAI (ca. 200 kb) contained some deletions and insertions as compared to the PAI of the reference strain MMH594, transferred precisely and integrated site-specifically into the chromosome of E. faecalis (intergenic region) and Enterococcus faecium (tRNAlys). The internal PAI structure was maintained after transfer. We assessed phenotypic changes accompanying acquisition of the PAI and expression of some of its determinants. The esp gene is expressed on the surface of donor and both transconjugants. Biofilm formation and cytolytic activity were enhanced in E. faecalis transconjugants after acquisition of the PAI. No differences in pathogenicity of E. faecalis were detected using a mouse bacteraemia and a mouse peritonitis models (tail vein and intraperitoneal injection). A 66 kb conjugative pheromone-responsive plasmid encoding erm(B) (pLG2) that was transferred in parallel with the PAI was sequenced. pLG2 is a pheromone responsive plasmid that probably promotes the PAI horizontal transfer, encodes antibiotic resistance features and contains complete replication and conjugation modules of enterococcal origin in a mosaic-like composition. The E. faecalis PAI can undergo precise intra- and interspecies transfer probably with the help of conjugative elements like conjugative resistance plasmids, supporting the role of horizontal gene transfer and antibiotic selective pressure in the successful establishment of certain enterococci as nosocomial pathogens.

High-level ciprofloxacin resistance among hospital-adapted Enterococcus faecium (CC17).

Hospital-adapted Enterococcus faecium differ from their colonising variants in humans and animals by additional genomic content. Molecular typing based on multilocus sequence typing (MLST) allows allocation of isolates to specific clonal complexes (CCs), such as CC17 for hospital-adapted strains. Acquired ampicillin resistance is a specific feature of these hospital isolates, especially in Europe. A few recent reports have described acquired high-level ciprofloxacin resistance as a supposed feature of hospital-adapted E. faecium strains. In the present retrospective analysis, ciprofloxacin minimum inhibitory concentrations (MICs) of 609 clinical isolates from German hospital patients (1997-2007) were determined and a breakpoint for high-level resistance was deduced (>16mg/L). Acquired high-level ciprofloxacin resistance was distributed among isolates of 26 different MLST types (all CC17), indicating a wide prevalence of this acquired resistance trait among the hospital-adapted E. faecium population. High-level ciprofloxacin resistance was linked to gyrA and parC mutations in 98 investigated isolates. Eleven different allele types or combinations thereof were identified. Their allocation to specific MLST and pulsed-field gel electrophoresis (PFGE) types revealed differences in the emergence and spread of corresponding mutations and strains.

FepA- and TonB-dependent bacteriophage H8: receptor binding and genomic sequence.

H8 is derived from a collection of Salmonella enterica serotype Enteritidis bacteriophage. Its morphology and genomic structure closely resemble those of bacteriophage T5 in the family Siphoviridae. H8 infected S. enterica serotypes Enteritidis and Typhimurium and Escherichia coli by initial adsorption to the outer membrane protein FepA. Ferric enterobactin inhibited H8 binding to E. coli FepA (50% inhibition concentration, 98 nM), and other ferric catecholate receptors (Fiu, Cir, and IroN) did not participate in phage adsorption. H8 infection was TonB dependent, but exbB mutations in Salmonella or E. coli did not prevent infection; only exbB tolQ or exbB tolR double mutants were resistant to H8. Experiments with deletion and substitution mutants showed that the receptor-phage interaction first involves residues distributed over the protein's outer surface and then narrows to the same charged (R316) or aromatic (Y260) residues that participate in the binding and transport of ferric enterobactin and colicins B and D. These data rationalize the multifunctionality of FepA: toxic ligands like bacteriocins and phage penetrate the outer membrane by parasitizing residues in FepA that are adapted to the transport of the natural ligand, ferric enterobactin. DNA sequence determinations revealed the complete H8 genome of 104.4 kb. A total of 120 of its 143 predicted open reading frames (ORFS) were homologous to ORFS in T5, at a level of 84% identity and 89% similarity. As in T5, the H8 structural genes clustered on the chromosome according to their function in the phage life cycle. The T5 genome contains a large section of DNA that can be deleted and that is absent in H8: compared to T5, H8 contains a 9,000-bp deletion in the early region of its chromosome, and nine potentially unique gene products. Sequence analyses of the tail proteins of phages in the same family showed that relative to pb5 (Oad) of T5 and Hrs of BF23, the FepA-binding protein (Rbp) of H8 contains unique acidic and aromatic residues. These side chains may promote binding to basic and aromatic residues in FepA that normally function in the adsorption of ferric enterobactin. Furthermore, a predicted H8 tail protein showed extensive identity and similarity to pb2 of T5, suggesting that it also functions in pore formation through the cell envelope. The variable region of this protein contains a potential TonB box, intimating that it participates in the TonB-dependent stage of the phage infection process.