New Antibody Weapons against an Old Foe

Antibodies have been used in a diagnostic capacity for many diseases and for identifying serotypes within single species of pathogens, notably between the multiple capsular polysaccharide serotypes of Streptococcus pneumoniae. For many years, the functions of antibodies in infection were thought to be limited to the opsonization of microorganisms followed by phagocytosis and to the fixing of complement. The thought that antibodies could have other functions has emerged only recently. The study by Yano and coworkers from the laboratory of Liise-anne Pirofski published in mBio [M. Yano, S. Gohil, J. R. Coleman, C. Manix, and L.-A. Pirofski, mBio 2(5):e00176-11, 2011] identifies one mechanism whereby nonopsonic antibodies enhance the transformation competence of two S. pneumoniae serotypes, which leads to an increase in genetic exchange and bacterial variability with a resulting population reduction through fratricide. These new and revealing antibody functions will add another chapter to the burgeoning story of the diversity and versatility of the immune response to bacteria

Production et validation d'un vaccin à agent inactivé contre la néphrite hémorragique entérite de l'oie (NHEO)

L'agent de la Néphrite Hémorragique Entérite de l'Oie (NHEO) est un polyomavirus, le GHPV (Goose hemorrhagic polymavirus), qui sévit de manière épizootique dans les élevages d'oies. Nous avons préparé un vaccin inactivé contre la NHEO pour vacciner les oies reproductrices - afin de transmettre aux oisons une protection basée sur les anticorps d'origine maternelle - et les oisons en croissance, pour les protéger pendant leur période de sensibilité à élevages d'oies. Nous avons préparé un vaccin la maladie. Le virus a été adapté à la culture sur cellules épithéliales de rein d'oison et les conditions de culture virale et de récupération du virus ont été optimisées. Afin de quantifier l'antigène viral, le virus a été titré avant inactivation par PCR quantitative. Nous avons par la suite défini un protocole d'inactivation du GHPV, basé sur l'incubation avec 0,3 % final de b-propiolactone. Après inactivation, l'antigène a été adjuvé avec de l'hydroxyde d'aluminium ou du Carbopolä. Un test sérologique ELISA a également été développé pour évaluer la réponse sérologique à la vaccination. Le vaccin et le test ELISA ont été validés à l'occasion d'essais sur des oies reproductrices et des oisons en croissance

Role of the Single-Stranded DNA–Binding Protein SsbB in Pneumococcal Transformation: Maintenance of a Reservoir for Genetic Plasticity

Bacteria encode a single-stranded DNA (ssDNA) binding protein (SSB) crucial for genome maintenance. In Bacillus subtilis and Streptococcus pneumoniae, an alternative SSB, SsbB, is expressed uniquely during competence for genetic transformation, but its precise role has been disappointingly obscure. Here, we report our investigations involving comparison of a null mutant (ssbB−) and a C-ter truncation (ssbBΔ7) of SsbB of S. pneumoniae, the latter constructed because SSBs' acidic tail has emerged as a key site for interactions with partner proteins. We provide evidence that SsbB directly protects internalized ssDNA. We show that SsbB is highly abundant, potentially allowing the binding of ∼1.15 Mb ssDNA (half a genome equivalent); that it participates in the processing of ssDNA into recombinants; and that, at high DNA concentration, it is of crucial importance for chromosomal transformation whilst antagonizing plasmid transformation. While the latter observation explains a long-standing observation that plasmid transformation is very inefficient in S. pneumoniae (compared to chromosomal transformation), the former supports our previous suggestion that SsbB creates a reservoir of ssDNA, allowing successive recombination cycles. SsbBΔ7 fulfils the reservoir function, suggesting that SsbB C-ter is not necessary for processing protein(s) to access stored ssDNA. We propose that the evolutionary raison d'être of SsbB and its abundance is maintenance of this reservoir, which contributes to the genetic plasticity of S. pneumoniae by increasing the likelihood of multiple transformation events in the same cell

Between-Strain Competition in Acquisition and Clearance of Pneumococcal Carriage—Epidemiologic Evidence From a Longitudinal Study of Day-Care Children

The state of pneumococcal carriage—that is, pneumococcal colonization in the nasopharynx of healthy persons—represents a reservoir for the spread of pneumococci among individuals. In light of the introduction of new pneumococcal conjugate vaccines, further knowledge on the dynamics of pneumococcal carriage is important. Different serotypes (strains) of pneumococcus are known to compete with each other in colonizing human hosts. Understanding the strength and mode of between-serotype competition is important because of its implications for vaccine-induced changes in the ecology of pneumococcal carriage. Competition may work through reduced acquisition of new serotypes, due to concurrent carriage in the individual, or through enhanced clearance of serotypes in carriers who harbor more than 1 serotype simultaneously. The authors employed longitudinal data (1999–2001) on pneumococcal carriage in Danish day-care children to analyze between-serotype competition. The data included observations of carriage in children who had not been vaccinated against pneumococcus, and the level of pneumococcal antibiotic resistance and antibiotic usage in the community was very low. Clearance of any single serotype was not affected by simultaneous carriage of other serotypes. In contrast, acquisition of other serotypes in already-colonized hosts was weak (relative rate of acquisition = 0.09, 95% credible interval: 0.05, 0.15)

A High-Resolution View of Genome-Wide Pneumococcal Transformation

Transformation is an important mechanism of microbial evolution through which bacteria have been observed to rapidly adapt in response to clinical interventions; examples include facilitating vaccine evasion and the development of penicillin resistance in the major respiratory pathogen Streptococcus pneumoniae. To characterise the process in detail, the genomes of 124 S. pneumoniae isolates produced through in vitro transformation were sequenced and recombination events detected. Those recombinations importing the selected marker were independent of unselected events elsewhere in the genome, the positions of which were not significantly affected by local sequence similarity between donor and recipient or mismatch repair processes. However, both types of recombinations were sometimes mosaic, with multiple non-contiguous segments originating from the same molecule of donor DNA. The lengths of the unselected events were exponentially distributed with a mean of 2.3 kb, implying that recombinations are stochastically resolved with a fixed per base probability of 4.4×10−4 bp−1. This distribution of recombination sizes, coupled with an observed under representation of large insertions within transferred sequence, suggests transformation has the potential to reduce the size of bacterial genomes, and is unlikely to act as an efficient mechanism for the uptake of accessory genomic loci

A new polyomavirus isolated in goose: from the identification of the virus toward the development of a vaccine

Hemorrhagic nephritis enteritis of geese (HNEG) is a major disease affecting goose. We have isolated its agent and shown that it is a novel member of Polyomavirus genus. The biology of this viral infection has been studied, at the level of both animal and flocks, on breeders and fattening goslings. An inactivated and adjuvanted vaccine has also been prepared and assayed on breeders and goslings. This program should result in the control of the disease on the field. It also addresses the question of the impact of polyomaviruses in animal and public health.La Néphrite hémorragique entérite de l'oie (NHEO) constitue une maladie majeure de l'oie. Nous avons récemment isolé son agent et montré qu'il s'agit d'une nouvelle espèce virale du genre Polyomavirus. La biologie de cette infection virale a été étudiée, à l'échelle de l'animal infecté et des populations d'oies, chez les reproducteurs et les oisons destinés au gavage. Un candidat vaccin, inactivé et adjuvé, a été préparé et testé chez les oies reproductrices et les oisons en croissance. Ce programme de recherche devrait permettre à terme le contrôle de l'affection sur le terrain. Il pose aussi la question de l'impact en santé animale, voire en santé publique, des polyomavirus

Competence in Streptococcus pneumoniae Is Regulated by the Rate of Ribosomal Decoding Errors

Competence for genetic transformation in Streptococcus pneumoniae develops in response to accumulation of a secreted peptide pheromone and was one of the initial examples of bacterial quorum sensing. Activation of this signaling system induces not only expression of the proteins required for transformation but also the production of cellular chaperones and proteases. We have shown here that activity of this pathway is sensitively responsive to changes in the accuracy of protein synthesis that are triggered by either mutations in ribosomal proteins or exposure to antibiotics. Increasing the error rate during ribosomal decoding promoted competence, while reducing the error rate below the baseline level repressed the development of both spontaneous and antibiotic-induced competence. This pattern of regulation was promoted by the bacterial HtrA serine protease. Analysis of strains with the htrA (S234A) catalytic site mutation showed that the proteolytic activity of HtrA selectively repressed competence when translational fidelity was high but not when accuracy was low. These findings redefine the pneumococcal competence pathway as a response to errors during protein synthesis. This response has the capacity to address the immediate challenge of misfolded proteins through production of chaperones and proteases and may also be able to address, through genetic exchange, upstream coding errors that cause intrinsic protein folding defects. The competence pathway may thereby represent a strategy for dealing with lesions that impair proper protein coding and for maintaining the coding integrity of the genome

Surviving Bacterial Sibling Rivalry: Inducible and Reversible Phenotypic Switching in Paenibacillus dendritiformis

Natural habitats vary in available nutrients and room for bacteria to grow, but successful colonization can lead to overcrowding and stress. Here we show that competing sibling colonies of Paenibacillus dendritiformis bacteria survive overcrowding by switching between two distinct vegetative phenotypes, motile rods and immotile cocci. Growing colonies of the rod-shaped bacteria produce a toxic protein, Slf, which kills cells of encroaching sibling colonies. However, sublethal concentrations of Slf induce some of the rods to switch to Slf-resistant cocci, which have distinct metabolic and resistance profiles, including resistance to cell wall antibiotics. Unlike dormant spores of P. dendritiformis, the cocci replicate. If cocci encounter conditions that favor rods, they secrete a signaling molecule that induces a switch to rods. Thus, in contrast to persister cells, P. dendritiformis bacteria adapt to changing environmental conditions by inducible and reversible phenotypic switching

Horizontal DNA transfer mechanisms of bacteria as weapons of intragenomic conflict

Horizontal DNA transfer (HDT) is a pervasive mechanism of diversification in many microbial species, but its primary evolutionary role remains controversial. Much recent research has emphasised the adaptive benefit of acquiring novel DNA, but here we argue instead that intragenomic conflict provides a coherent framework for understanding the evolutionary origins of HDT. To test this hypothesis, we developed a mathematical model of a clonally descended bacterial population undergoing HDT through transmission of mobile genetic elements (MGEs) and genetic transformation. Including the known bias of transformation toward the acquisition of shorter alleles into the model suggested it could be an effective means of counteracting the spread of MGEs. Both constitutive and transient competence for transformation were found to provide an effective defence against parasitic MGEs; transient competence could also be effective at permitting the selective spread of MGEs conferring a benefit on their host bacterium. The coordination of transient competence with cell-cell killing, observed in multiple species, was found to result in synergistic blocking of MGE transmission through releasing genomic DNA for homologous recombination while simultaneously reducing horizontal MGE spread by lowering the local cell density. To evaluate the feasibility of the functions suggested by the modelling analysis, we analysed genomic data from longitudinal sampling of individuals carrying Streptococcus pneumoniae. This revealed the frequent within-host coexistence of clonally descended cells that differed in their MGE infection status, a necessary condition for the proposed mechanism to operate. Additionally, we found multiple examples of MGEs inhibiting transformation through integrative disruption of genes encoding the competence machinery across many species, providing evidence of an ongoing "arms race." Reduced rates of transformation have also been observed in cells infected by MGEs that reduce the concentration of extracellular DNA through secretion of DNases. Simulations predicted that either mechanism of limiting transformation would benefit individual MGEs, but also that this tactic's effectiveness was limited by competition with other MGEs coinfecting the same cell. A further observed behaviour we hypothesised to reduce elimination by transformation was MGE activation when cells become competent. Our model predicted that this response was effective at counteracting transformation independently of competing MGEs. Therefore, this framework is able to explain both common properties of MGEs, and the seemingly paradoxical bacterial behaviours of transformation and cell-cell killing within clonally related populations, as the consequences of intragenomic conflict between self-replicating chromosomes and parasitic MGEs. The antagonistic nature of the different mechanisms of HDT over short timescales means their contribution to bacterial evolution is likely to be substantially greater than previously appreciated