Host Tropism and Structural Biology of ABC Toxin Complexes

ABC toxin complexes are a class of protein toxin translocases comprised of a multimeric assembly of protein subunits. Each subunit displays a unique composition, contributing to the formation of a syringe-like nano-machine with natural cargo carrying, targeting, and translocation capabilities. Many of these toxins are insecticidal, drawing increasing interest in agriculture for use as biological pesticides. The A subunit (TcA) is the largest subunit of the complex and contains domains associated with membrane permeation and targeting. The B and C subunits, TcB and TcC, respectively, package into a cocoon-like structure that contains a toxic peptide and are coupled to TcA to form a continuous channel upon final assembly. In this review, we outline the current understanding and gaps in the knowledge pertaining to ABC toxins, highlighting seven published structures of TcAs and how these structures have led to a better understanding of the mechanism of host tropism and toxin translocation. We also highlight similarities and differences between homologues that contribute to variations in host specificity and conformational change. Lastly, we review the biotechnological potential of ABC toxins as both pesticides and cargo-carrying shuttles that enable the transport of peptides into cells.

Bacterial biopesticides: Biodiversity, role in pest management and beneficial impact on agricultural and environmental sustainability

Agro-environmental sustainability is based upon the adoption of efficient resources in agro-practices that have a nominal impact on the ecosystem. Insect pests are responsible for causing severe impacts on crop productivity. Wide ranges of agro-chemicals have been employed over the last 50 years to overcome crop yield losses due to insect pests. But better knowledge about the hazards due to chemical pesticides and other pest resistance and resurgence issues necessitates an alternative for pest control. The applications of biological pesticides offer a best alternate that is safe, cost-effective, easy to adoption and successful against various insect pests and pathogens. Like other organisms, insects can get a wide range of diseases from various microbes, such as bacteria, fungi, viruses, protozoa, and nematodes. In order to create agricultural pest management practices that are environmentally beneficial, bacterial entomopathogens are being thoroughly studied. Utilization of bacterial biopesticides has been adopted for the protection of agricultural products. The different types of toxin complexes released by various microorganisms and their mechanisms of action are recapitulated. The present review described the diversity and biocontrol prospective of certain bacteria and summarised the potential of bacterial biopesticides for the management of agricultural pests, insects, and other phytopathogenic microorganisms in agricultural practices.

The ABC toxin complex from Yersinia entomophaga can package three different cytotoxic components expressed from distinct genetic loci in an unfolded state: the structures of both shell and cargo

Bacterial ABC toxin complexes (Tcs) comprise three core proteins: TcA, TcB and TcC. The TcA protein forms a pentameric assembly that attaches to the surface of target cells and penetrates the cell membrane. The TcB and TcC proteins assemble as a heterodimeric TcB-TcC subcomplex that makes a hollow shell. This TcB-TcC subcomplex self-cleaves and encapsulates within the shell a cytotoxic `cargo' encoded by the C-terminal region of the TcC protein. Here, we describe the structure of a previously uncharacterized TcC protein from Yersinia entomophaga, encoded by a gene at a distant genomic location from the genes encoding the rest of the toxin complex, in complex with the TcB protein. When encapsulated within the TcB-TcC shell, the C-terminal toxin adopts an unfolded and disordered state, with limited areas of local order stabilized by the chaperone-like inner surface of the shell. We also determined the structure of the toxin cargo alone and show that when not encapsulated within the shell, it adopts an ADP-ribosyltransferase fold most similar to the catalytic domain of the SpvB toxin from Salmonella typhimurium. Our structural analysis points to a likely mechanism whereby the toxin acts directly on actin, modifying it in a way that prevents normal polymerization.

Stepwise assembly and release of Tc toxins from Yersinia entomophaga

Tc toxins are virulence factors of bacterial pathogens. Although their structure and intoxication mechanism are well understood, it remains elusive where this large macromolecular complex is assembled and how it is released. Here we show by an integrative multiscale imaging approach that Yersinia entomophaga Tc (YenTc) toxin components are expressed only in a subpopulation of cells that are 'primed' with several other potential virulence factors, including filaments of the protease M66/StcE. A phage-like lysis cassette is required for YenTc release; however, before resulting in complete cell lysis, the lysis cassette generates intermediate 'ghost' cells, which may serve as assembly compartments and become packed with assembled YenTc holotoxins. We hypothesize that this stepwise mechanism evolved to minimize the number of cells that need to be killed. The occurrence of similar lysis cassettes in diverse organisms indicates a conserved mechanism for Tc toxin release that may apply to other extracellular macromolecular machines.

Yersinia entomophaga Tc toxin is released by T10SS-dependent lysis of specialized cell subpopulations

Disease-causing bacteria secrete numerous toxins to invade and subjugate their hosts. Unlike many smaller toxins, the secretion machinery of most large toxins remains enigmatic. By combining genomic editing, proteomic profiling and cryo-electron tomography of the insect pathogen Yersinia entomophaga, we demonstrate that a specialized subset of these cells produces a complex toxin cocktail, including the nearly ribosome-sized Tc toxin YenTc, which is subsequently exported by controlled cell lysis using a transcriptionally coupled, pH-dependent type 10 secretion system (T10SS). Our results dissect the Tc toxin export process by a T10SS, identifying that T10SSs operate via a previously unknown lytic mode of action and establishing them as crucial players in the size-insensitive release of cytoplasmically folded toxins. With T10SSs directly embedded in Tc toxin operons of major pathogens, we anticipate that our findings may model an important aspect of pathogenesis in bacteria with substantial impact on agriculture and healthcare.

Enterobacter Strain IPPBiotE33 Displays a Synergistic Effect with Bacillus thuringiensis Bt185

The discovery and isolation of new non-Bt insecticidal bacteria and genes are significant for the development of new biopesticides against coleopteran pests. In this study, we evaluated the insecticidal activity of non-Bt insecticidal bacteria, PPBiotE33, IPPBiotC41, IPPBiotA42 and IPPBiotC43, isolated from the peanut rhizosphere. All these strains showed insecticidal activity against first- and third-instar larvae of Holotrichia parallela, Holotrichia oblita, Anomala corpulenta and Potosia brevitarsis. IPPBiotE33 showed the highest toxicity among the four strains and exhibited virulence against Colaphellus bowringi. The genome of IPPBiotE33 was sequenced, and a new protein, 03673, with growth inhibition effects on C. bowringi was obtained. In addition, IPPBiotE33 had a synergistic effect with Bacillus thuringiensis Bt185 against H. parallela in bioassays and back-inoculation experiments with peanut seedlings. IPPBiotE33 induced a decrease in hemocytes and an increase in phenol oxidase activity in H. parallela hemolymph, known as the immunosuppressive effect, which mediated synergistic activity with Bt185. This study increased our knowledge of the new insecticidal strain IPPBiotE33 and shed new light on the research on new insecticidal coaction mechanisms and new blended pesticides.

Yersiniomics, a Multi-Omics Interactive Database for Yersinia Species

The genus Yersinia includes a large variety of nonpathogenic and life-threatening pathogenic bacteria, which cause a broad spectrum of diseases in humans and animals, such as plague, enteritis, Far East scarlet-like fever (FESLF), and enteric redmouth disease. Like most clinically relevant microorganisms, Yersinia spp. are currently subjected to intense multi-omics investigations whose numbers have increased extensively in recent years, generating massive amounts of data useful for diagnostic and therapeutic developments. The lack of a simple and centralized way to exploit these data led us to design Yersiniomics, a web-based platform allowing straightforward analysis of Yersinia omics data. Yersiniomics contains a curated multi-omics database at its core, gathering 200 genomic, 317 transcriptomic, and 62 proteomic data sets for Yersinia species. It integrates genomic, transcriptomic, and proteomic browsers, a genome viewer, and a heatmap viewer to navigate within genomes and experimental conditions. For streamlined access to structural and functional properties, it directly links each gene to GenBank, the Kyoto Encyclopedia of Genes and Genomes (KEGG), UniProt, InterPro, IntAct, and the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and each experiment to Gene Expression Omnibus (GEO), the European Nucleotide Archive (ENA), or the Proteomics Identifications Database (PRIDE). Yersiniomics provides a powerful tool for microbiologists to assist with investigations ranging from specific gene studies to systems biology studies. IMPORTANCE The expanding genus Yersinia is composed of multiple nonpathogenic species and a few pathogenic species, including the deadly etiologic agent of plague, Yersinia pestis. In 2 decades, the number of genomic, transcriptomic, and proteomic studies on Yersinia grew massively, delivering a wealth of data. We developed Yersiniomics, an interactive web-based platform, to centralize and analyze omics data sets on Yersinia species. The platform allows user-friendly navigation between genomic data, expression data, and experimental conditions. Yersiniomics will be a valuable tool to microbiologists.

Identification of genes involved in exoprotein release using a high-throughput exoproteome screening assay in Yersinia entomophaga

Bacterial protein secretion is crucial to the maintenance of viability and pathogenicity. Although many bacterial secretion systems have been identified, the underlying mechanisms regulating their expression are less well explored. Yersinia entomophaga MH96, an entomopathogenic bacterium, releases an abundance of proteins including the Yen-Tc into the growth medium when cultured in Luria Bertani broth at ≤ 25°C. Through the development of a high-throughput exoproteome screening assay (HESA), genes involved in MH96 exoprotein production were identified. Of 4,080 screened transposon mutants, 34 mutants exhibited a decreased exoprotein release, and one mutation located in the intergenic region of the Yen-Tc operon displayed an elevated exoprotein release relative to the wild-type strain MH96. DNA sequencing revealed several transposon insertions clustered in gene regions associated with lipopolysaccharide (LPSI and LPSII), and N-acyl-homoserine lactone synthesis (quorum sensing). Twelve transposon insertions were located within transcriptional regulators or intergenic regions. The HESA will have broad applicability for identifying genes associated with exoproteome production in a range of microorganisms.

Identification of Diverse Toxin Complex Clusters and an eCIS Variant in Serratia proteamaculans Pathovars of the New Zealand Grass Grub (Costelytra Giveni) and Manuka Beetle (Pyronota Spp.) Larvae

The grass grub endemic to New Zealand, Costelytra giveni (Coleoptera: Scarabaeidae), and the manuka beetle, Pyronota festiva and P. setosa (Coleoptera: Scarabaeidae), are prevalent pest species. Through assessment of bacterial strains isolated from diseased cadavers of these insect species, 19 insect-active Serratia proteamaculans variants and a single Serratia entomophila strain were isolated. When independently bioassayed, these isolates differed in host range, the rate of disease progression, and 12-day mortality rates, which ranged from 60 to 100% of the challenged larvae. A Pyronota spp.-derived S. proteamaculans isolate caused a transient disease phenotype in challenged C. giveni larvae, whereby larvae appeared diseased before recovering to a healthy state. Genome sequence analysis revealed that all but two of the sequenced isolates contained a variant of the S. entomophila amber-disease-associated plasmid, pADAP. Each isolate also encoded one of seven distinct members of the toxin complex (Tc) family of insect-active toxins, five of which are newly described, or a member of the extracellular contractile injection (eCIS) machine family, with a new AfpX variant designated SpF. Targeted mutagenesis of each of the predicted Tc- or eCIS-encoding regions abolished or attenuated pathogenicity. Host-range testing showed that several of the S. proteamaculans Tc-encoding isolates affected both Pyronota and C. giveni species, with other isolates specific for either Pyronota spp. or C. giveni. The isolation of several distinct host-specific pathotypes of Serratia spp. may reflect pathogen-host speciation. IMPORTANCE New pathotypes of the insect pathogen Serratia, each with differing virulence attributes and host specificity toward larvae of the New Zealand manuka beetle and grass grub, have been identified. All of the Serratia proteamaculans isolates contained one of seven different insect-active toxin clusters or one of three eCIS variants. The diversity of these Serratia-encoded virulence clusters, resulting in differences in larval disease progression and host specificity in endemic scarab larvae, suggests speciation of these pathogens with their insect hosts. The differing virulence properties of these Serratia species may affect their potential infectivity and distribution among the insect populations. Based on their differing geographic isolation and pathotypes, several of these Serratia isolates, including the manuka beetle-active isolates, are likely to be more effective biopesticides in specific environments or could be used in combination for greater effect.

Yersinia massiliensis (Enterobacteriales: Enterobacteriaceae) in the host Anaphes nitens (Hymenoptera: Mymaridae): first report of association with insects

Endosymbiont bacteria can affect biological parameters and reduce the effectiveness of natural enemies in controlling the target insect. The objective of this work was to identify endosymbiont bacteria in Anaphes nitens (Girault, 1928) (Hymenoptera: Mymaridae), the main natural enemy used to manage Gonipterus platensis (Marelli, 1926) (Coleoptera: Curculionidae). Genomic DNA from six A. nitens populations was extracted and polymerase chain reactions (PCR) were performed with the primers to detect endosymbiont bacteria in this insect. The PCR products were amplified, sequenced, and compared with sequences deposited in the GenBank for the bacteria identification. All A. nitens populations had the bacterium Yersinia massiliensis (Enterobacteriales: Enterobacteriaceae). This bacterium was originally described as free-living, and it is associated with and composes part of the A. nitens microbiota. This is the first report of Y. massiliensis in an insect host.

Identification of a Novel Brevibacillus laterosporus Strain With Insecticidal Activity Against Aedes albopictus Larvae

Bacterial species able to produce proteins that are toxic against insects have been discovered at the beginning of the last century. However, up to date only two of them have been used as pesticides in mosquito control strategies targeting larval breeding sites: Bacillus thuringensis var. israelensis and Lysinibacillus sphaericus. Aiming to expand the arsenal of biopesticides, bacterial cultures from 44 soil samples were assayed for their ability to kill larvae of Aedes albopictus. A method to select, grow and test the larvicidal capability of spore-forming bacteria from each soil sample was developed. This allowed identifying 13 soil samples containing strains capable of killing Ae. albopictus larvae. Among the active isolates, one strain with high toxicity was identified as Brevibacillus laterosporus by 16S rRNA gene sequencing and by morphological characterization using transmission electron microscopy. The new isolate showed a larvicidal activity significantly higher than the B. laterosporus LMG 15441 reference strain. Its genome was phylogenomically characterized and compared to the available Brevibacillus genomes. Thus, the new isolate can be considered as a candidate adjuvant to biopesticides formulations that would help preventing the insurgence of resistance.

Diversification of OmpA and OmpF of Yersinia ruckeri is independent of the underlying species phylogeny and evidence of virulence-related selection

Yersinia ruckeri is the causative agent of enteric redmouth disease (ERM) which causes economically significant losses in farmed salmonids, especially Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss, Walbaum). However, very little is known about the genetic relationships of disease-causing isolates in these two host species or about factors responsible for disease. Phylogenetic analyses of 16 representative isolates based on the nucleotide sequences of 19 housekeeping genes suggests that pathogenic Atlantic salmon and rainbow trout isolates represent distinct host-specific lineages. However, the apparent phylogenies of certain isolates has been influenced by horizontal gene transfer and recombinational exchange. Splits decomposition analysis demonstrated a net-like phylogeny based on the housekeeping genes, characteristic of recombination. Comparative analysis of the distribution of individual housekeeping gene alleles across the isolates demonstrated evidence of genomic mosaicism and recombinational exchange involving certain Atlantic salmon and rainbow trout isolates. Comparative nucleotide sequence analysis of the key outer membrane protein genes ompA and ompF revealed that the corresponding gene trees were both non-congruent with respect to the housekeeping gene phylogenies providing evidence that horizontal gene transfer has influenced the evolution of both these surface protein-encoding genes. Analysis of inferred amino acid sequence variation in OmpA identified a single variant, OmpA.1, that was present in serotype O1 and O8 isolates representing typical pathogenic strains in rainbow trout and Atlantic salmon, respectively. In particular, the sequence of surface-exposed loop 3 differed by seven amino acids to that of other Y. ruckeri isolates. These findings suggest that positive selection has likely influenced the presence of OmpA.1 in these isolates and that loop 3 may play an important role in virulence. Amino acid sequence variation of OmpF was greater than that of OmpA and was similarly restricted mainly to the surface-exposed loops. Two OmpF variants, OmpF.1 and OmpF.2, were associated with pathogenic rainbow trout and Atlantic salmon isolates, respectively. These OmpF proteins had very similar amino acid sequences suggesting that positive evolutionary pressure has also favoured the selection of these variants in pathogenic strains infecting both species.

In vivo transcriptome analysis provides insights into host-dependent expression of virulence factors by Yersinia entomophaga MH96, during infection of Galleria mellonella

The function of microbes can be inferred from knowledge of genes specifically expressed in natural environments. Here, we report the in vivo transcriptome of the entomopathogenic bacterium Yersinia entomophaga MH96, captured during initial, septicemic, and pre-cadaveric stages of intrahemocoelic infection in Galleria mellonella. A total of 1285 genes were significantly upregulated by MH96 during infection; 829 genes responded to in vivo conditions during at least one stage of infection, 289 responded during two stages of infection, and 167 transcripts responded throughout all three stages of infection compared to in vitro conditions at equivalent cell densities. Genes upregulated during the earliest infection stage included components of the insecticidal toxin complex Yen-TC (chi1, chi2, and yenC1), genes for rearrangement hotspot element containing protein yenC3, cytolethal distending toxin cdtAB, and vegetative insecticidal toxin vip2. Genes more highly expressed throughout the infection cycle included the putative heat-stable enterotoxin yenT and three adhesins (usher-chaperone fimbria, filamentous hemagglutinin, and an AidA-like secreted adhesin). Clustering and functional enrichment of gene expression data also revealed expression of genes encoding type III and VI secretion system-associated effectors. Together these data provide insight into the pathobiology of MH96 and serve as an important resource supporting efforts to identify novel insecticidal agents.

Advances in Entomopathogen Isolation: A Case of Bacteria and Fungi

Entomopathogenic bacteria and fungi are quite frequently found in soils and insect cadavers. The first step in utilizing these microbes as biopesticides is to isolate them, and several culture media and insect baiting procedures have been tested in this direction. In this work, the authors review the current techniques that have been developed so far, in the last five decades, and display brief protocols which can be adopted for the isolations of these entomopathogens. Among bacteria, this review focuses on Serratia spp. and bacteria from the class Bacilli. Among fungi, the review focuses those from the order Hypocreales, for example, genera Beauveria, Clonostachys, Lecanicillium, Metarhizium, and Purpureocillium. The authors chose these groups of entomopathogenic bacteria and fungi based on their importance in the microbial biopesticide market.

Assessment of toxicity and persistence of Yersinia entomophaga and its Yen-Tc associated toxin

BACKGROUND

The insect-pathogenic bacterium Yersinia entomophaga MH96 is currently under development as a microbial pesticide active against various pasture and crop pests such as the diamondback moth Plutella xylostella and the cotton bollworm Helicoverpa armigeria. To enable nonrestricted field trials of Y. entomophaga MH96, information on the persistence and nontarget effects of the bacterium and its Yen-Tc proteinaceous toxin are required.

RESULTS

The Y. entomophaga Yen-Tc associated toxin was found to have limited persistence on foliage and is inactivated by UV light. The Yen-Tc was rapidly degraded in ovine or bovine rumen fluid or the intestinal fluid of H. armigera. In H. armigera an intestinal protein of >50 kDa was found to cleave the Yen-Tc bond. Assessment of Y. entomophaga persistence on foliage and in soil found that after 42 days the bacterium could not be detected in soil at 20% soil moisture content but persisted for 72 days at 30-40% soil moisture. Nontarget effects of Y. entomophaga towards earthworms found that the bacterium afforded no adverse effects on worm growth or behavior. A summary of historic Yen-Tc and Y. entomophaga persistence and toxicity data is presented.

CONCLUSION

The bacterium Y. entomophaga and its Yen-Tc associated toxin have limited persistence in the environment, with the Yen-Tc being susceptible to UV inactivation and proteolytic degradation, and the bacterium persisting longer in soil of a high moisture content. © 2020 Society of Chemical Industry.

Potential for a biopesticide bait to control black beetle, Heteronychus arator (Coleoptera: Scarabaeidae)

BACKGROUND

Yersinia entomophaga is an entomopathogenic bacterium that is active against scarab beetles, among other insects. In New Zealand, the African black beetle, Heteronychus arator (Coleoptera: Scarabaeidae), is a major pest of pastures and arable crops but very few control options exist and no insecticides are registered for use in established pastures.

RESULTS

In laboratory bioassays, H. arator adults were susceptible to a bait containing Y. entomophaga at low doses. This bait was more effective against H. arator adults during spring than autumn in small-scale field plots (320 mm diameter). A large-scale field trial (40 × 40 m plots) reduced adult numbers substantially: approximately twice as many beetles were captured in pitfall traps from untreated plots compared with plots treated with the Y. entomophaga bait at 70 kg ha^-1 . This single bait application in spring also reduced subsequent larval populations in summer.

CONCLUSIONS

Heteronychus arator is a difficult pest to manage using chemical insecticides. This biopesticide with Y. entomophaga as the active ingredient offers a new solution for New Zealand pastures, with potential for application to other crops affected by H. arator and for control of other pests. © 2020 Society of Chemical Industry.

Persistence of Yersinia enterocolitica bio-serotype 4/O:3 in a pork production chain in Minas Gerais, Brazil

Yersinia enterocolitica bio-serotype 4/O:3 was previously identified in a pork production chain in Brazil and the obtained isolates presented high identity by pulsed-field gel electrophoresis (PFGE, XbaI). For the current study, an additional 147 porcine samples (tonsils = 100, palate = 30, head meat = 17) were collected from the same pork production chain 2-years later and 14 (9.5%) tested positive for Y. enterocolitica. Isolates (n = 24, 1 to 2 per positive sample) were bio-serotype 4/O:3 and harbored virulence genes ail, inv, wbbU, virF, myfA, ystA, ymoA, hreP and sat, and the multidrug resistance related genes emrD, marC and yfhD. PFGE (XbaI) demonstrated no differences among isolates (100% similarity) and were identical to some Y. enterocolitica isolates (n = 13) obtained previously from the same pork chain. A second PFGE analysis (NotI) confirmed the high degree of similarity among isolates obtained over time, demonstrating the persistence of an apparent clonal Y. enterocolitica bio-serotype 4/O:3 in this particular pork production chain in Brazil.

Performance and Application of 16S rRNA Gene Cycle Sequencing for Routine Identification of Bacteria in the Clinical Microbiology Laboratory

This review provides a state-of-the-art description of the performance of Sanger cycle sequencing of the 16S rRNA gene for routine identification of bacteria in the clinical microbiology laboratory. A detailed description of the technology and current methodology is outlined with a major focus on proper data analyses and interpretation of sequences. The remainder of the article is focused on a comprehensive evaluation of the application of this method for identification of bacterial pathogens based on analyses of 16S multialignment sequences. In particular, the existing limitations of similarity within 16S for genus- and species-level differentiation of clinically relevant pathogens and the lack of sequence data currently available in public databases is highlighted. A multiyear experience is described of a large regional clinical microbiology service with direct 16S broad-range PCR followed by cycle sequencing for direct detection of pathogens in appropriate clinical samples. The ability of proteomics (matrix-assisted desorption ionization-time of flight) versus 16S sequencing for bacterial identification and genotyping is compared. Finally, the potential for whole-genome analysis by next-generation sequencing (NGS) to replace 16S sequencing for routine diagnostic use is presented for several applications, including the barriers that must be overcome to fully implement newer genomic methods in clinical microbiology. A future challenge for large clinical, reference, and research laboratories, as well as for industry, will be the translation of vast amounts of accrued NGS microbial data into convenient algorithm testing schemes for various applications (i.e., microbial identification, genotyping, and metagenomics and microbiome analyses) so that clinically relevant information can be reported to physicians in a format that is understood and actionable. These challenges will not be faced by clinical microbiologists alone but by every scientist involved in a domain where natural diversity of genes and gene sequences plays a critical role in disease, health, pathogenicity, epidemiology, and other aspects of life-forms. Overcoming these challenges will require global multidisciplinary efforts across fields that do not normally interact with the clinical arena to make vast amounts of sequencing data clinically interpretable and actionable at the bedside.

Biopesticides in India: technology and sustainability linkages

Despite enhancing the crop yields, the so called green revolution (GR) has proven unsuccessful in assuring long term agricultural sustainability. The methods used for productivity enhancement during GR have not only proven to be problematic but have also resulted in deterioration of soil quality and several other issues related to ecosystems and health issues. The damage was mainly caused by the indiscriminate use of chemical fertilizers and insecticides. Various types of pesticides, are now known to be causing huge problems in the agro-ecosystems. In such a situation, where chemicals have caused or are causing irreversible impacts on agroecosystems, the use of biopesticides has emerged as a sustainable alternative leading to safe organic farming. At the global level, environmentally benign nature and target-specificity of biopesticides are gaining wide popularity. However, in developing countries like India usage of biopesticides is still minuscule in comparison to conventional chemical pesticides. Although the Indian government has encouraged the use of biopesticides by placing them into many of the agricultural schemes, at the grassroots level, biopesticides are facing many challenges. The lower adaptability and declining interest of farmers towards biopesticides have become a matter of concern. However, technological challenges related to production, manufacture and application in agroecosystems have also raised a question on their long-term sustainability. The main objective of this review is to highlight the developing trend in the field of biocontrol products in India. Apart from this, the review also focuses on the technological perspectives that are required for the long-term sustainability of biological control products in Indian agriculture and market.

Development of a Yersinia entomophaga bait for control of larvae of the porina moth (Wiseana spp.), a pest of New Zealand improved grassland systems

BACKGROUND

Porina is the common name for moths and larvae of the genus Wiseana (Lepidoptera: Hepialidae), some of which are significant pasture pests in New Zealand. Because of environmental concerns and the non-target effects of insecticide control measures, biological alternatives for the control of insect pests such as porina are required.

RESULTS

Using a food preference assay and time-lapse photography, a range of low-cost food ingredients were assessed for their palatability to porina larvae. Lead candidates were combined into extruded bait variants, allowing assessment of their palatability to porina larvae. A composite bait consisting of palatable ingredients was developed, into which the porina-active entomopathogen Yersinia entomophaga was incorporated. A 7 day minimum median lethal dose of approximately 6.0 × ±1 × 10⁶ Y. entomophaga cells per 0.02 g of bait was defined. Field trials showed that the mean change in larval density over time differed between treatments, with Y. entomophaga bait applied at 87 kg ha^-1 resulting in a mean 65% reduction in larval density relative to the control plots, and diflubenzuron treatment resulting in a mean 77% reduction relative to the control plots. The mean dry matter yields over the course of the trial were highest for diflubenzuron (5029 kg ha^-1 ), followed by the Y. entomophaga (4783 kg ha^-1 ) and control (4673 kg ha^-1 ) treatments.

CONCLUSIONS

The bacterium Y. entomophaga applied as a composite bait offers an environmentally sustainable approach for porina pest control. © 2019 Society of Chemical Industry.

Genus-wide Yersinia core-genome multilocus sequence typing for species identification and strain characterization

The genus Yersinia comprises species that differ widely in their pathogenic potential and public-health significance. Yersinia pestis is responsible for plague, while Yersinia enterocolitica is a prominent enteropathogen. Strains within some species, including Y. enterocolitica, also vary in their pathogenic properties. Phenotypic identification of Yersinia species is time-consuming, labour-intensive and may lead to incorrect identifications. Here, we developed a method to automatically identify and subtype all Yersinia isolates from their genomic sequence. A phylogenetic analysis of Yersinia isolates based on a core subset of 500 shared genes clearly demarcated all existing Yersinia species and uncovered novel, yet undefined Yersinia taxa. An automated taxonomic assignment procedure was developed using species-specific thresholds based on core-genome multilocus sequence typing (cgMLST). The performance of this method was assessed on 1843 isolates prospectively collected by the French National Surveillance System and analysed in parallel using phenotypic reference methods, leading to nearly complete (1814; 98.4 %) agreement at species and infra-specific (biotype and serotype) levels. For 29 isolates, incorrect phenotypic assignments resulted from atypical biochemical characteristics or lack of phenotypic resolution. To provide an identification tool, a database of cgMLST profiles and reference taxonomic information has been made publicly accessible (https://bigsdb.pasteur.fr/yersinia). Genomic sequencing-based identification and subtyping of any Yersinia is a powerful and reliable novel approach to define the pathogenic potential of isolates of this medically important genus.

Heterogeneity of Highly Susceptible Yersinia enterocolitica Isolates of Clinical and Environmental Origin: A 5-Year Survey from Iran (2011-2016)

The aim of this study was to evaluate the resistance and virulence characteristics of Yersinia enterocolitica strains of clinical and environmental origins over a 5-year period in Iran and to determine the genetic diversity of strains using pulsed-field gel electrophoresis (PFGE) method. A total of 20 Y. enterocolitica strains were collected from 850 stool samples of patients with diarrhea, and 18 Yersinia spp. including 10 Y. enterocolitica were collected from water, food, and vegetable samples. The most frequently isolated Y. enterocolitica strains belonged to biotype (BT) 1A (83.33%). No Y. enterocolitica BT4 was detected that can be attributed to the absence of pig animal reservoir in Iranian food chain. The most frequent chromosomal virulence genes among the Y. enterocolitica isolates were inv (100%), ystA (67%), ystB (83%), tccC (20%), and ail (17%). The most frequent chromosomal virulence genes among non-enterocolitica Yersinia spp. isolates were ystB (87.5%), ystA (37.5%), and inv (37.5%). None of the Y. enterocolitica isolates harbored plasmid origin virulence genes. None of the isolates was resistant to ciprofloxacin, gentamicin, tetracycline, cotrimoxazole, and chloramphenicol, whereas 90% of the Y. enterocolitica and 62.5% of the Yersinia spp. strains were resistant to ampicillin. PFGE genotyping showed a heterogeneous population of highly susceptible Yersinia spp. in both clinical and environmental samples, putting forward a good prognosis in the treatment of patients with yersiniosis. The occurrence of biotype 1A with inv⁺ystA⁺ystB⁺ genotype in clinical strains implies the significance of inv, ystA, and ystB gene products in turning of naturally nonpathogenic biotype 1A strains into clinically important pathogens.

Mechanisms of resistance to commercially relevant entomopathogenic bacteria

Bacteria represent the most commercially successful entomopathogenic microbial group, with most commercialized insecticides containing gram-positive bacteria in the Bacillaceae family. Resistance to entomopathogenic bacteria threatens sustainable agriculture, and information on the mechanisms and genes involved is vital to develop management practices aimed at reducing this risk. We provide an integrative summary on mechanisms responsible for resistance to commercialized entomopathogenic bacteria, including information on resistance to transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt crops). The available experimental evidence identifies alterations in binding of insecticidal proteins to receptors in the host as the main mechanism for high levels of resistance to entomopathogenic bacteria.

Yersinia kristensenii subsp. rochesterensis subsp. nov., isolated from human feces

A single bacterial isolate, EPLC-04^T, was isolated from human feces and identified as representing a member of the genus Yersinia on the basis of phenotypic characteristics, matrix assisted laser desorption ionization time-of-flight mass spectrometry and partial 16S rRNA gene sequencing. The isolate's phenotypic profile differed from that described for the most closely related species, Yersinia kristensenii, by exhibiting lipase production and lacking pyrazinamidase activity. Multiple genetic targets, including the complete (1465 bp) 16S rRNA gene sequence and partial sequences of groEL (539 bp), gyrB (935 bp), glnA (525 bp) and recA (535 bp) indicated that the isolate exhibited 98.91, 92.16, 90.81, 92.78 and 89.01 % identity with Yersinia aldovae, 98.98, 91.99, 90.17, 89.77 and 89.55 % identity with Yersinia intermedia, and 99.66, 98.11, 98.50, 98.49 and 98.51 % identity with Y. kristensenii, respectively. Phylogenetic reconstructions based on the combination of the four housekeeping genes indicated that the isolate formed a unique branch, supported by a bootstrap value of 100 %. Digital DNA-DNA homology and 16S rRNA gene sequencing identified EPLC-04^T as representing Y. kristensenii. However, the unique phenotypic traits and results of phylogenetic analysis indicate that it represents a novel subspecies of Y. kristensenii. The name Yersinia kristenseniisubsp. rochesterensis subsp. nov. is proposed for this novel taxon (type strain EPLC-04^T=ATCC BAA-2637^T, DSMZ 28595^T).

Cryo-EM structures of the pore-forming A subunit from the Yersinia entomophaga ABC toxin

ABC toxins are pore-forming virulence factors produced by pathogenic bacteria. YenTcA is the pore-forming and membrane binding A subunit of the ABC toxin YenTc, produced by the insect pathogen Yersinia entomophaga. Here we present cryo-EM structures of YenTcA, purified from the native source. The soluble pre-pore structure, determined at an average resolution of 4.4 Å, reveals a pentameric assembly that in contrast to other characterised ABC toxins is formed by two TcA-like proteins (YenA1 and YenA2) and decorated by two endochitinases (Chi1 and Chi2). We also identify conformational changes that accompany membrane pore formation by visualising YenTcA inserted into liposomes. A clear outward rotation of the Chi1 subunits allows for access of the protruding translocation pore to the membrane. Our results highlight structural and functional diversity within the ABC toxin subfamily, explaining how different ABC toxins are capable of recognising diverse hosts.

Assessment of Yersinia entomophaga as a control agent of the diamondback moth Plutella xylostella

The application of the biocontrol bacterium Yersinia entomophaga as a foliar spray was assessed for its efficacy against larvae of the diamondback moth, Plutella xylostella. The bacterium was applied as either a broth suspension, or as a biopolymer-based gel foliar spray and compared with commercial insecticides Dipel (Bacillus thuringiensis) and Spinosad. The performance of Y. entomophaga was comparable with that of Dipel. The gel-based formulation extended leaf persistence over that of the basic broth culture spray, while also providing higher initial foliar deposition rates. The bacterium was found to multiply within the P. xylostella larvae to 5.8 × 10⁵ cells per larva, while the median lethal dose (LD₅₀) was determined to be 2.69 × 10³ cells per larva. Importantly, B. thuringiensis Cry1A-resistant, Cry1C-resistant, indoxacarb/pyrethroid-resistant, and Spinosad-resistant P. xylostella larvae were susceptible to Y. entomophaga.

Insecticidal Toxicity of Yersinia frederiksenii Involves the Novel Enterotoxin YacT

The genus Yersinia comprises 19 species of which three are known as human and animal pathogens. Some species display toxicity toward invertebrates using the so-called toxin complex (TC) and/or determinants that are not yet known. Recent studies showed a remarkable variability of insecticidal activities when representatives of different Yersinia species (spp.) were subcutaneously injected into the greater wax moth, Galleria mellonella. Here, we demonstrate that Y. intermedia and Y. frederiksenii are highly toxic to this insect. A member of Y. Enterocolitica phylogroup 1B killed G. mellonella larvae with injection doses of approximately 38 cells only, thus resembling the insecticidal activity of Photorhabdus luminescens. The pathogenicity Yersinia spp. displays toward the larvae was higher at 15°C than at 30°C and independent of the TC. However, upon subtraction of all genes of the low-pathogenic Y. enterocolitica strain W22703 from the genomes of Y. intermedia and Y. frederiksenii, we identified a set of genes that may be responsible for the toxicity of these two species. Indeed, a mutant of Y. frederiksenii lacking yacT, a gene that encodes a protein similar to the heat-stable cytotonic enterotoxin (Ast) of Aeromonas hydrophila, exhibited a reduced pathogenicity toward G. mellonella larvae and altered the morphology of hemocytes. The data suggests that the repertoire of virulence determinants present in environmental Yersinia species remains to be elucidated.

First isolation of Yersinia entomophaga in human urinary tract

Yersinia entomophaga is an insect pathogen first isolated from larvae of Coleoptera in New Zealand in 2011. We report here the first isolation of Y. entomophaga from human urine. Using whole-genome sequencing, we confirmed the presence of specific chromosomal virulence genes and identified a plasmid harbouring a quinolone resistance gene.

Serratia proteamaculans Strain AGR96X Encodes an Antifeeding Prophage (Tailocin) with Activity against Grass Grub (Costelytra giveni) and Manuka Beetle (Pyronota Species) Larvae

A highly virulent Serratia proteamaculans strain, AGR96X, exhibiting specific pathogenicity against larvae of the New Zealand grass grub (Costelytra giveni; Coleoptera: Scarabaeidae) and the New Zealand manuka beetle (Pyronota festiva and P. setosa; Coleoptera: Scarabaeidae), was isolated from a diseased grass grub larva. A 12-day median lethal dose of 4.89 × 10³ ± 0.92 × 10³ cells per grass grub larva was defined for AGR96X, and death occurred within 5 to 12 days following the ingestion of a high bacterial dose. During the infection period, the bacterium rapidly multiplied within the insect host and invaded the hemocoel, leading to a mean bacterial load of 8.2 × 10⁹ cells per larva at 6 days postingestion. Genome sequencing of strain AGR96X revealed the presence of a variant of the Serratia entomophila antifeeding prophage (Afp), a tailocin designated AfpX. Unlike Afp, AfpX contains two Afp16 tail-length termination protein orthologs and two putative toxin components. A 37-kb DNA fragment encoding the AfpX-associated region was cloned, transformed into Escherichia coli, and fed to C. giveni and Pyronota larvae, causing mortality. In addition, the deletion of the afpX15 putative chaperone component abolished the virulence of AGR96X. Unlike S. entomophila Afp, the AfpX tailocin could be induced by mitomycin C. Transmission electron microscopy analysis revealed the presence of Afp-like particles of various lengths, and when the purified AfpX tailocin was fed to grass grub or manuka beetle larvae, they underwent phenotypic changes similar to those of larvae fed AGR96X.IMPORTANCESerratia proteamaculans strain AGR96X shows dual activity against larvae of endemic New Zealand pasture pests, the grass grub (Costelytra giveni) and the manuka beetle (Pyronota spp.). Unlike Serratia entomophila, the causal agent of amber disease, which takes 3 to 4 months to kill grass grub larvae, AGR96X causes mortality within 5 to 12 days of ingestion and invades the insect hemocoel. AGR96X produces a unique variant of the S. entomophila antifeeding prophage (Afp), a cell-free phage-like entity that is proposed to deliver protein toxins to the grass grub target site, causing a cessation of feeding activity. Unlike other Afp variants, AGR96X Afp, named AfpX, contains two tail-length termination proteins, resulting in greater variability in the AfpX length. AfpX shows dual activity against both grass grub and manuka beetle larvae. AGR96X is a viable alternative to S. entomophila for pest control in New Zealand pasture systems.

Main Groups of Microorganisms of Relevance for Food Safety and Stability

Microbiology is important to food safety, production, processing, preservation, and storage. Microbes such as bacteria, molds, and yeasts are employed for the foods production and food ingredients such as production of wine, beer, bakery, and dairy products. On the other hand, the growth and contamination of spoilage and pathogenic microorganisms is considered as one of the main causes to loss of foodstuff nowadays. Although technology, hygienic strategies, and traceability are important factors to prevent and delay microbial growth and contamination, food remains susceptible to spoilage and activity of pathogen microorganisms. Food loss by either spoilage or contaminated food affects food industry and consumers leading to economic losses and increased hospitalization costs. This chapter focuses on general aspects, characteristics, and importance of main microorganisms (bacteria, yeasts, molds, virus, and parasites) involved in food spoilage or contamination: known and recently discovered species; defects and alterations in foodstuff; most common food associated with each foodborne disease; resistance to thermal processing; occurrence in different countries; outbreaks; and associated symptoms.

Structure and gene cluster of a tyvelose-containing O-polysaccharide of an entomopathogenic bacterium Yersinia entomophaga MH96T related to Yersinia pseudotuberculosis

An O-polysaccharide was isolated from the lipopolysaccharide of an entomopathogenic bacterium Yersinia entomophaga MH96^T by mild acid hydrolysis and studied by 2D NMR spectroscopy. The following structure of the branched tetrasaccharide repeating unit of the polysaccharide was established: where Tyv indicates 3,6-dideoxy-d-arabino-hexose (tyvelose). The structure established is consistent with the gene content of the O-antigen gene cluster. The O-polysaccharide structure and gene cluster of Y. entomophaga are related to those of some Y. pseudotuberculosis serotypes.

Dispersal of the Invasive Pasture Pest Heteronychus arator into Areas of Low Population Density: Effects of Sex and Season, and Implications for Pest Management

African black beetle, Heteronychus arator (Scarabaeidae), is an exotic pest of pastures in northern New Zealand. Both adults and larvae feed on pasture grasses. Adults disperse by walking (short range) or flying (long range). Dispersal flights are triggered by warm night temperatures in spring and autumn. Short range adult dispersal in search of mates, food or oviposition sites is poorly understood. This study investigated walking activity of H. arator adults over three seasons in New Zealand pastures. Adult walking activity was monitored using pitfall traps along fence lines and in pasture plots on a dairy farm in Waikato, New Zealand, in spring 2013, spring 2014, and autumn 2015. Beetle populations were reduced by application of a biopesticide bait to compare walking activity between treated and control plots for up to 26 days post-treatment. Marked beetles were released into the pasture plots to measure the distance traveled by recaptured individuals. Trap catches along the fence lines were correlated with air temperatures in 2013. Trap catches were male biased in spring 2014 compared with autumn 2015. Trap numbers in the control plots were nearly double that of treated plots in both seasons. More beetles were caught in the pitfall traps at the edges of the treated plots than in the center. Trap catches were consistent throughout the control plot in spring 2014, but in autumn 2015 more beetles were caught in the center of the control plot than at the edges. Few marked beetles were recaptured with dispersal rates estimated as <0.5 m per day. Warmer temperatures encouraged short range dispersal in H. arator. Males were more active than females during the spring mating season. Edge effects were strong and should be considered in the design of field experiments.

'Add, stir and reduce': Yersinia spp. as model bacteria for pathogen evolution

Pathogenic species in the Yersinia genus have historically been targets for research aimed at understanding how bacteria evolve into mammalian pathogens. The advent of large-scale population genomic studies has greatly accelerated the progress in this field, and Yersinia pestis, Yersinia pseudotuberculosis and Yersinia enterocolitica have once again acted as model organisms to help shape our understanding of the evolutionary processes involved in pathogenesis. In this Review, we highlight the gene gain, gene loss and genome rearrangement events that have been identified by genomic studies in pathogenic Yersinia species, and we discuss how these findings are changing our understanding of pathogen evolution. Finally, as these traits are also found in the genomes of other species in the Enterobacteriaceae, we suggest that they provide a blueprint for the evolution of enteropathogenic bacteria.

The Draft Genome Sequence of the Yersinia entomophaga Entomopathogenic Type Strain MH96T

Here we report the draft genome of Yersinia entomophaga type strain MH96T. The genome shows 93.8% nucleotide sequence identity to that of Yersinia nurmii type strain APN3a-cT, and comprises a single chromosome of approximately 4,275,531 bp. In silico analysis identified that, in addition to the previously documented Y. entomophaga Yen-TC gene cluster, the genome encodes a diverse array of toxins, including two type III secretion systems, and five rhs-associated gene clusters. As well as these multicomponent systems, several orthologs of known insect toxins, such as VIP2 toxin and the binary toxin PirAB, and distant orthologs of some mammalian toxins, including repeats-in-toxin, a cytolethal distending toxin, hemolysin-like genes and an adenylate cyclase were identified. The genome also contains a large number of hypothetical proteins and orthologs of known effector proteins, such as LopT, as well as genes encoding a wide range of proteolytic determinants, including metalloproteases and pathogen fitness determinants, such as genes involved in iron metabolism. The bioinformatic data derived from the current in silico analysis, along with previous information on the pathobiology of Y. entomophaga against its insect hosts, suggests that a number of these virulence systems are required for survival in the hemocoel and incapacitation of the insect host.

Complete genome sequence and comparative genome analysis of a new special Yersinia enterocolitica

Yersinia enterocolitica is the most diverse species among the Yersinia genera and shows more polymorphism, especially for the non-pathogenic strains. Individual non-pathogenic Y. enterocolitica strains are wrongly identified because of atypical phenotypes. In this study, we isolated an unusual Y. enterocolitica strain LC20 from Rattus norvegicus. The strain did not utilize urea and could not be classified as the biotype. API 20E identified Escherichia coli; however, it grew well at 25 °C, but E. coli grew well at 37 °C. We analyzed the genome of LC20 and found the whole chromosome of LC20 was collinear with Y. enterocolitica 8081, and the urease gene did not exist on the genome which is consistent with the result of API 20E. Also, the 16 S and 23 SrRNA gene of LC20 lay on a branch of Y. enterocolitica. Furthermore, the core-based and pan-based phylogenetic trees showed that LC20 was classified into the Y. enterocolitica cluster. Two plasmids (80 and 50 k) from LC20 shared low genetic homology with pYV from the Yersinia genus, one was an ancestral Yersinia plasmid and the other was novel encoding a number of transposases. Some pathogenic and non-pathogenic Y. enterocolitica-specific genes coexisted in LC20. Thus, although it could not be classified into any Y. enterocolitica biotype due to its special biochemical metabolism, we concluded the LC20 was a Y. enterocolitica strain because its genome was similar to other Y. enterocolitica and it might be a strain with many mutations and combinations emerging in the processes of its evolution.

Purification of the Yersinia entomophaga Yen-TC Toxin Complex Using Size Exclusion Chromatography

The Yersinia entomophaga toxin complex (Yen-TC) is the bacterium's main virulence determinant. Because of its high insect activity, methods were developed to allow the routine isolation and purification of Yen-TC from an overnight bacterial culture using size exclusion chromatography. Here we outline an overnight purification procedure using a 100-ml culture volume, where approximately 2 mg of Yen-TC, with an approximate purity of 95-98 %, can be routinely obtained.

Taxonomy of Yersinia pestis

This chapter summarized the taxonomy and typing works of Yersinia pestis since it's firstly identified in Hong Kong in 1894. Phenotyping methods that based on phenotypic characteristics, including biotyping, serotyping, antibiogram analysis, bacteriocin typing, phage typing, and plasmid typing, were firstly applied in classification of Y. pestis in subspecies level. And then, with the advancement of molecular biological technology, the methods based on outer membrane protein profiles, fatty acid composition, and bacterial mass fingerprinting were also used to identify the populations within Y. pestis. However, Y. pestis is a highly homogenous species; therefore, the above typing methods could only provide low resolution, e.g., only one serotype and one phage type were observed for the whole species. Since the 1990s, molecular typing based on DNA variations, including single-nucleotide polymorphism, gene gain/loss, variable-number tandem repeats, clustered regularly interspaced short palindromic repeat, etc., was introduced and improved the resolution and robust of typing result. Especially in recent years, genotyping-based whole-genome-wide variations were successfully employed in Y. pestis, which built the "gold standard" of typing scheme of the species and could distinguish the samples under the strain level. The taxonomy and typing works leaved us enormous polymorphism data; therefore, a comprehensive fingerprint database of Y. pestis was needed to collect and standardize these data, for facilitating future works on evolution, plague surveillance and control, anti-bioterrorism, and microbial forensic researches.

Temperature-Dependent Galleria mellonella Mortality as a Result of Yersinia entomophaga Infection

The bacterium Yersinia entomophaga is pathogenic to a range of insect species, with death typically occurring within 2 to 5 days of ingestion. Per os challenge of larvae of the greater wax moth (Galleria mellonella) confirmed that Y. entomophaga was virulent when fed to larvae held at 25°C but was avirulent when fed to larvae maintained at 37°C. At 25°C, a dose of ~4 × 10(7) CFU per larva of a Y. entomophaga toxin complex (Yen-TC) deletion derivative, the Y. entomophaga ΔTC variant, resulted in 27% mortality. This low level of activity was restored to near-wild-type levels by augmentation of the diet with a sublethal dose of purified Yen-TC. Intrahemocoelic injection of ~3 Y. entomophaga or Y. entomophaga ΔTC cells per larva gave a 4-day median lethal dose, with similar levels of mortality observed at both 25 and 37°C. Following intrahemocoelic injection of a Yen-TC YenA1 green fluorescent protein fusion strain into larvae maintained at 25°C, the bacteria did not fluoresce until the population density reached 2 × 10(7) CFU ml(-1) of hemolymph. The observed cells also took an irregular form. When the larvae were maintained at 37°C, the cells were small and the observed fluorescence was sporadic and weak, being more consistent at a population density of ~3 × 10(9) CFU ml(-1) of hemolymph. These findings provide further understanding of the pathobiology of Y. entomophaga in insects, showing that the bacterium gains direct access to the hemocoelic cavity, from where it rapidly multiplies to cause disease.

Pulsed-field gel electrophoresis and multi locus sequence typing for characterizing genotype variability of Yersinia ruckeri isolated from farmed fish in France

Yersinia ruckeri is a pathogen that has an impact on aquaculture worldwide. The disease caused by this bacterial species, yersiniosis or redmouth disease, generates substantial economic losses due to the associated mortality and veterinary costs. For predicting outbreaks and improving control strategies, it is important to characterize the population structure of the bacteria. The phenotypic and genetic homogeneities described previously indicate a clonal population structure as observed in other fish bacteria. In this study, the pulsed-field gel electrophoresis (PFGE) and multi locus sequence typing (MLST) methods were used to describe a population of isolates from outbreaks on French fish farms. For the PFGE analysis, two enzymes (NotI and AscI) were used separately and together. Results from combining the enzymes showed the great homogeneity of the outbreak population with a similarity > 80.0% but a high variability within the cluster (cut-off value = 80.0%) with a total of 43 pulsotypes described and an index of diversity = 0.93. The dominant pulsotypes described with NotI (PtN4 and PtN7) have already been described in other European countries (Finland, Germany, Denmark, Spain and Italy). The MLST approach showed two dominant sequence types (ST31 and ST36), an epidemic structure of the French Y. ruckeri population and a preferentially clonal evolution for rainbow trout isolates. Our results point to multiple types of selection pressure on the Y. ruckeri population attributable to geographical origin, ecological niche specialization and movements of farmed fish.

The Yersinia pseudotuberculosis complex: characterization and delineation of a new species, Yersinia wautersii

The genus Yersinia contains three species pathogenic for humans, one of which is the enteropathogen Yersinia pseudotuberculosis. A recent analysis by Multi Locus Sequence Typing (MLST) of the 'Y. pseudotuberculosis complex' revealed that this complex comprises three distinct populations: the Y. pestis/Y. pseudotuberculosis group, the recently described species Yersinia similis, and a third not yet characterized population designated 'Korean Group', because most strains were isolated in Korea. The aim of this study was to perform an in depth phenotypic and genetic characterization of the three populations composing the Y. pseudotuberculosis complex (excluding Y. pestis, which belonged to the Y. pseudotuberculosis cluster in the MLST analysis). Using a set of strains representative of each group, we found that the three populations had close metabolic properties, but were nonetheless distinguishable based on D-raffinose and D-melibiose fermentation, and on pyrazinamidase activity. Moreover, high-resolution electrospray mass spectrometry highlighted protein peaks characteristic of each population. Their 16S rRNA gene sequences shared high identity (≥99.5%), but specific nucleotide signatures for each group were identified. Multi-Locus Sequence Analysis also identified three genetically closely related but distinct populations. Finally, an Average Nucleotide Identity (ANI) analysis performed after sequencing the genomes of a subset of strains of each group also showed that intragroup identity (average for each group ≥99%) was higher than intergroup diversity (94.6-97.4%). Therefore, all phenotypic and genotypic traits studied concurred with the initial MLST data indicating that the Y. pseudotuberculosis complex comprises a third and clearly distinct population of strains forming a novel Yersinia species that we propose to designate Yersinia wautersii sp. nov. The isolation of some strains from humans, the detection of virulence genes (on the pYV and pVM82 plasmids, or encoding the superantigen ypmA) in some isolates, and the absence of pyrazinamidase activity (a hallmark of pathogenicity in the genus Yersinia) argue for the pathogenic potential of Y. wautersii.

Homology analysis of pathogenic Yersinia species Yersinia enterocolitica, Yersinia pseudotuberculosis, and Yersinia pestis based on multilocus sequence typing

We developed a multilocus sequence typing (MLST) scheme and used it to study the population structure and evolutionary relationships of three pathogenic Yersinia species. MLST of these three Yersinia species showed a complex of two clusters, one composed of Yersinia pseudotuberculosis and Yersinia pestis and the other composed of Yersinia enterocolitica. Within the first cluster, the predominant Y. pestis sequence type 90 (ST90) was linked to Y. pseudotuberculosis ST43 by one locus difference, and 81.25% of the ST43 strains were from serotype O:1b, supporting the hypothesis that Y. pestis descended from the O:1b serotype of Y. pseudotuberculosis. We also found that the worldwide-prevalent serotypes O:1a, O:1b, and O:3 were predominated by specific STs. The second cluster consisted of pathogenic and nonpathogenic Y. enterocolitica strains, two of which may not have identical STs. The pathogenic Y. enterocolitica strains formed a relatively conserved group; most strains clustered within ST186 and ST187. Serotypes O:3, O:8, and O:9 were separated into three distinct blocks. Nonpathogenic Y. enterocolitica STs were more heterogeneous, reflecting genetic diversity through evolution. By providing a better and effective MLST procedure for use with the Yersinia community, valuable information and insights into the genetic evolutionary differences of these pathogens were obtained.

Role of Yersinia pestis toxin complex family proteins in resistance to phagocytosis by polymorphonuclear leukocytes

Yersinia pestis carries homologues of the toxin complex (Tc) family proteins, which were first identified in other Gram-negative bacteria as having potent insecticidal activity. The Y. pestis Tc proteins are neither toxic to fleas nor essential for survival of the bacterium in the flea, even though tc gene expression is highly upregulated and much more of the Tc proteins YitA and YipA are produced in the flea than when Y. pestis is grown in vitro. We show that Tc(+) and Tc(-) Y. pestis strains are transmitted equivalently from coinfected fleas, further demonstrating that the Tc proteins have no discernible role, either positive or negative, in transmission by the flea vector. Tc proteins did, however, confer Y. pestis with increased resistance to killing by polymorphonuclear leukocytes (PMNs). Resistance to killing was not the result of decreased PMN viability or increased intracellular survival but instead correlated with a Tc protein-dependent resistance to phagocytosis that was independent of the type III secretion system (T3SS). Correspondingly, we did not detect T3SS-dependent secretion of the native Tc proteins YitA and YipA or the translocation of YitA- or YipA-β-lactamase fusion proteins into CHO-K1 (CHO) cells or human PMNs. Thus, although highly produced by Y. pestis within the flea and related to insecticidal toxins, the Tc proteins do not affect interaction with the flea or transmission. Rather, the Y. pestis Tc proteins inhibit phagocytosis by mouse PMNs, independent of the T3SS, and may be important for subverting the mammalian innate immune response immediately following transmission from the flea.

Yersinia enterocolitica and Photorhabdus asymbiotica β-lactamases BlaA are exported by the twin-arginine translocation pathway

In general, β-lactamases of medically important Gram-negative bacteria are Sec-dependently translocated into the periplasm. In contrast, β-lactamases of Mycobacteria spp. (BlaC, BlaS) and the Gram-negative environmental bacteria Stenotrophomonas maltophilia (L2) and Xanthomonas campestris (Bla(XCC-1)) have been reported to be secreted by the twin-arginine translocation (Tat) system. Yersinia enterocolitica carries 2 distinct β-lactamase genes (blaA and blaB) encoding BlaA(Ye) and the AmpC-like β-lactamase BlaB, respectively. By using the software PRED-TAT for prediction and discrimination of Sec from Tat signal peptides, we identified a functional Tat signal sequence for Yersinia BlaA(Ye). The Tat-dependent translocation of BlaA(Ye) could be clearly demonstrated by using a Y. enterocolitica tatC-mutant and cell fractionation. Moreover, we could demonstrate a unique unusual temperature-dependent activity profile of BlaA(Ye) ranging from 15 to 60 °C and a high 'melting temperature' (T(M)=44.3°) in comparison to the related Sec-dependent β-lactamase TEM-1 (20-50°C, T(M)=34.9 °C). Strikingly, the blaA gene of Y. enterocolitica is present in diverse environmental Yersinia spp. and a blaA homolog gene could be identified in the closely related Photorhabdus asymbiotica (BlaA(Pa); 69% identity to BlaA(Ye)). For BlaA(Pa) of P. asymbiotica, we could also demonstrate Tat-dependent secretion. These results suggest that Yersinia BlaA-related β-lactamases may be the prototype of a large Tat-dependent β-lactamase family, which originated from environmental bacteria.

Type II secretion in Yersinia-a secretion system for pathogenicity and environmental fitness

In Yersinia species, type III secretion (T3S) is the most prominent and best studied secretion system and a hallmark for the infection process of pathogenic Yersinia species. Type II secretion (T2S), on the other hand, is less well-characterized, although all Yersinia species, pathogenic as well as non-pathogenic, possess one or even two T2S systems. The only Yersinia strain in which T2S has so far been studied is the human pathogenic strain Y. enterocolitica 1b. Mouse infection experiments showed that at least one of the two T2S systems of Y. enterocolitica 1b, termed Yts1, is involved in dissemination and colonization of deeper tissues like liver and spleen. Interestingly, in vitro studies revealed a complex regulation of the Yts1 system, which is mainly active at low temperatures and high Mg²⁺-levels. Furthermore, the functional characterization of the proteins secreted in vitro indicates a role of the Yts1 machinery in survival of the bacteria in an environmental habitat. In silico analyses identified Yts1 homologous systems in bacteria that are known as plant symbionts or plant pathogens. Thus, the recent studies point to a dual function of the Yts1 T2S systems, playing a role in virulence of humans and animals, as well as in the survival of the bacteria outside of the mammalian host. In contrast, the role of the second T2S system, Yts2, remains ill defined. Whereas the T3S system and its virulence-mediating role has been intensively studied, it might now be time to also focus on the T2S system and its role in the Yersinia lifestyle, especially considering that most of the Yersinia isolates are not found in infected humans but have been gathered from various environmental samples.