Coexistence Of Strains Research Articles

Complete genome analysis of porcine kobuviruses from the feces of pigs in Japan.

Porcine kobuviruses (PoKoVs) are ubiquitously distributed in pig populations worldwide and are thought to be enteric viruses in swine. Although PoKoVs have been detected in pigs in Japan, no complete genome data for Japanese PoKoVs are available. In the present study, 24 nearly complete or complete sequences of the PoKoV genome obtained from 10 diarrheic feces and 14 non-diarrheic feces of Japanese pigs were analyzed using a metagenomics approach. Japanese PoKoVs shared 85.2-100% identity with the complete coding nucleotide (nt) sequences and the closest relationship of 85.1-98.3% with PoKoVs from other countries. Twenty of 24 Japanese PoKoVs carried a deletion of 90 nt in the 2B coding region. Phylogenetic tree analyses revealed that PoKoVs were not grouped according to their geographical region of origin and the phylogenetic trees of the L, P1, P2, and P3 genetic regions showed topologies different from each other. Similarity plot analysis using strains from a single farm revealed partially different similarity patterns among strains from identical farm origins, suggesting that recombination events had occurred. These results indicate that various PoKoV strains are prevalent and not restricted geographically on pig farms worldwide and the coexistence of multiple strains leads to recombination events of PoKoVs and contributes to the genetic diversity and evolution of PoKoVs.

Interstrain Cooperation in Meningococcal Biofilms: Role of Autotransporters NalP and AutA.

Neisseria meningitidis (Nm) and Neisseria lactamica (Nl) are commensal bacteria that live in the human nasopharynx, where they form microcolonies. In contrast to Nl, Nm occasionally causes blood and/or meningitis infection with often fatal consequences. Here, we studied interactions between neisserial strains during biofilm formation. Fluorescent strains were engineered and analyzed for growth in single- and dual-strain biofilms with confocal laser-scanning microscopy. Different strains of diverse Neisseria species formed microcolonies of different sizes and morphologies. Pair-wise combinations of two invasive Nm strains and one Nm carrier isolate showed that these strains can coexist in spite of the fact that they produce toxins to combat congeners. This lack of competition was even observed when the biofilms were formed under nutrient limitation and can be explained by the observation that the separate microcolonies within mixed biofilms are mostly lineage specific. However, these microcolonies showed different levels of interaction. The coexistence of two strains was also observed in mixed biofilms of Nm and Nl strains. Inactivation of the autotransporter NalP, which prevents the release of the heparin-binding antigen NHBA and the α-peptide of IgA protease from the cell surface, and/or the production of autotransporter AutA increased interactions between microcolonies, as evidenced by close contacts between microcolonies on the substratum. Qualitative and quantitative analysis revealed an altered spatial distribution of each strain in mixed biofilms with consequences for the biomass, biofilm architecture and bacterial viability depending on the synthesis of NalP and AutA, the expression of which is prone to phase variation. Being in a consortium resulted in some cases in commensalism and cooperative behavior, which promoted attachment to the substratum or increased survival, possibly as result of the shared use of the biofilm matrix. We hypothesize that Nm strains can cooperate during host colonization, but, possibly, the different capacities of the microcolonies of each strain to resist the host's defenses limits the long-term coexistence of strains in the host.

Evolution of antibiotic resistance is linked to any genetic mechanism affecting bacterial duration of carriage

Understanding how changes in antibiotic consumption affect the prevalence of antibiotic resistance in bacterial pathogens is important for public health. In a number of bacterial species, including Streptococcus pneumoniae, the prevalence of resistance has remained relatively stable despite prolonged selection pressure from antibiotics. The evolutionary processes allowing the robust coexistence of antibiotic sensitive and resistant strains are not fully understood. While allelic diversity can be maintained at a locus by direct balancing selection, there is no evidence for such selection acting in the case of resistance. In this work, we propose a mechanism for maintaining coexistence at the resistance locus: linkage to a second locus that is under balancing selection and that modulates the fitness effect of resistance. We show that duration of carriage plays such a role, with long duration of carriage increasing the fitness advantage gained from resistance. We therefore predict that resistance will be more common in strains with a long duration of carriage and that mechanisms maintaining diversity in duration of carriage will also maintain diversity in antibiotic resistance. We test these predictions in S. pneumoniae and find that the duration of carriage of a serotype is indeed positively correlated with the prevalence of resistance in that serotype. These findings suggest heterogeneity in duration of carriage is a partial explanation for the coexistence of sensitive and resistant strains and that factors determining bacterial duration of carriage will also affect the prevalence of resistance.

Co-feeding transmission facilitates strain coexistence in Borrelia burgdorferi, the Lyme disease agent

Coexistence of multiple tick-borne pathogens or strains is common in natural hosts and can be facilitated by resource partitioning of the host species, within-host localization, or by different transmission pathways. Most vector-borne pathogens are transmitted horizontally via systemic host infection, but transmission may occur in the absence of systemic infection between two vectors feeding in close proximity, enabling pathogens to minimize competition and escape the host immune response. In a laboratory study, we demonstrated that co-feeding transmission can occur for a rapidly-cleared strain of Borrelia burgdorferi, the Lyme disease agent, between two stages of the tick vector Ixodes scapularis while feeding on their dominant host, Peromyscus leucopus. In contrast, infections rapidly became systemic for the persistently infecting strain. In a field study, we assessed opportunities for co-feeding transmission by measuring co-occurrence of two tick stages on ears of small mammals over two years at multiple sites. Finally, in a modeling study, we assessed the importance of co-feeding on R0, the basic reproductive number. The model indicated that co-feeding increases the fitness of rapidly-cleared strains in regions with synchronous immature tick feeding. Our results are consistent with increased diversity of B. burgdorferi in areas of higher synchrony in immature feeding – such as the midwestern United States. A higher relative proportion of rapidly-cleared strains, which are less human pathogenic, would also explain lower Lyme disease incidence in this region. Finally, if co-feeding transmission also occurs on refractory hosts, it may facilitate the emergence and persistence of new pathogens with a more limited host range.

Dynamical properties and thresholds of an HIV model with super-infection.

Super-infection by multiple HIV-1 subtypes, previously thought restricted to high risk groups, has now been reported in the general heterosexual populations at relatively the same incidence rate as in high risk groups. We present a simple deterministic HIV model with super-infection by two HIV-1 subtypes. Mathematical characteristics including the basic reproductive number $(\mathcal{R}_0)$, invasion threshold $(\mathcal{R}_{21},\mathcal{R}_{12})$ and conditions for asymptotic stability are derived. In the absence of super-infection the model exhibits competitive exclusion, and all equilibria are globally attracting if they exist except for the disease free which is a saddle for $\mathcal{R}_0>1.$ The results show that the subtype with the dominant reproductive number exceeding unity dominates the weaker subtype forcing it to extinction regardless of the size of the reproductive number. On the other end, super-infection may promote subtype co-existence whenever the minimum of the subtype specific reproductive numbers $(\mathcal{R}_1,\mathcal{R}_2)$ and the invasion reproductive numbers $(\mathcal{R}_{12},\mathcal{R}_{21})$ exceed unity. Our results demonstrate that if the partial reproductive numbers $(\mathcal{R}_1~\mbox{and}~\mathcal{R}_2 )$ and the invasion reproductive number for the weaker subtype $(\mathcal{R}_{21})$ satisfy $\mathcal{R}_2<1,~\mathcal{R}_1>1~\mbox{and}~\mathcal{R}_{21}>1,$ then primary infection by subtype $1$ may stay the extinction of subtype $2$ despite its relatively low reproductive fitness. For certain parameter ranges, hysteresis (including backward bifurcation) occurs with possible differences in the asymptotic level of disease prevalence. Super-infection may thus facilitate the continued re-generation of reproductively noncompetent subtypes whose subtype specific reproductive numbers will be less than unity while at the same time allowing for the mutual coexistence and persistence of multiple strains. Persistence and co-existence of multiple strains has detrimental effect on vaccine design and development and administration of ART where one or more of the strains are drug resistant.

Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut.

With the increasing amount of evidence linking certain disorders of the human body to a disturbed gut microbiota, there is a growing interest for compounds that positively influence its composition and activity through diet. Besides the consumption of probiotics to stimulate favorable bacterial communities in the human gastrointestinal tract, prebiotics such as inulin-type fructans (ITF) and arabinoxylan-oligosaccharides (AXOS) can be consumed to increase the number of bifidobacteria in the colon. Several functions have been attributed to bifidobacteria, encompassing degradation of non-digestible carbohydrates, protection against pathogens, production of vitamin B, antioxidants, and conjugated linoleic acids, and stimulation of the immune system. During life, the numbers of bifidobacteria decrease from up to 90% of the total colon microbiota in vaginally delivered breast-fed infants to <5% in the colon of adults and they decrease even more in that of elderly as well as in patients with certain disorders such as antibiotic-associated diarrhea, inflammatory bowel disease, irritable bowel syndrome, obesity, allergies, and regressive autism. It has been suggested that the bifidogenic effects of ITF and AXOS are the result of strain-specific yet complementary carbohydrate degradation mechanisms within cooperating bifidobacterial consortia. Except for a bifidogenic effect, ITF and AXOS also have shown to cause a butyrogenic effect in the human colon, i.e., an enhancement of colon butyrate production. Butyrate is an essential metabolite in the human colon, as it is the preferred energy source for the colon epithelial cells, contributes to the maintenance of the gut barrier functions, and has immunomodulatory and anti-inflammatory properties. It has been shown that the butyrogenic effects of ITF and AXOS are the result of cross-feeding interactions between bifidobacteria and butyrate-producing colon bacteria, such as Faecalibacterium prausnitzii (clostridial cluster IV) and Anaerostipes, Eubacterium, and Roseburia species (clostridial cluster XIVa). These kinds of interactions possibly favor the co-existence of bifidobacterial strains with other bifidobacteria and with butyrate-producing colon bacteria in the human colon.

Peri-implant and periodontal microbiome diversity in aggressive periodontitis patients: a pilot study.

To investigate the bacterial microbiome in periodontal and peri-implant biofilms deriving from aggressive periodontitis patients (AgP) in conditions of health and disease. Ninety-one plaque samples were collected from 18 patients previously diagnosed and treated for AgP. The samples were taken from (i) 24 residual periodontal pockets (TD) (n=6 patients), (ii) 24 healthy periodontal sites (TH) (n=6 patients), (iii) 24 dental sites from the same implant patients (TM) (n=6 patients), (iv) 5 peri-implantitis sites (II) (n=2 patients), (v) 6 peri-mucositis sites (IM) (n=2 patients) and (vi) 8 healthy implant sites (IH) (n=2 patients). All subjects underwent periodontal clinical and radiographic assessments. Bacterial DNA was extracted, PCR amplified using 16S rRNA gene V5-V7 primers (barcoded amplicons 785F;1175R), purified, pooled at equimolar concentrations and sequenced (MiSeq, Illumina) yielding 250bp paired-end reads. The 16S rRNA reads were filtered, assembled and analysed. The genera Propionibacterium, Paludibacter, Staphylococcus, Filifactor, Mogibacterium, Bradyrhizobium and Acinetobacter were unique to peri-implant sites (P=0.05). In TM samples, different proportions and bacterial spp. were found when compared with the same patients' samples at implant sites. Specifically, Actinomyces (P=0.013) and Corynebacterium (P=0.030) genera showed to be significantly more abundant in the TM group when compared to the II. The highest phylogenetic diversity was observed in residual periodontal pocket sites (TD). Increased annual tooth loss rate and residual pocketing was related to high proportions of the genera Actinomyces, Porphyromonas, Prevotella, Streptococcus, Actinomycetaceae, TM7-3, Selenomonas, and Dialister, Treponema, Parvimonas and Peptostreptococcus in the TD group. Within the limitations of this pilot study, the periodontal and peri-implant microbiome presents a dissimilar taxonomic composition across different niches within AgP patients. The host response, the habitat structure and the vast coexistence of strains and species surrounding implants and teeth in health and disease are likely to be shaping the heterogeneous composition of the subgingival biofilms. The TM7 phylum was found only in TD cases. The investigation of the impact of periodontal and peri-implant keystone species on these complex ecosystems in states of health and disease seems to be essential.

Pathogen Propagation Model with Superinfection in Vegetatively Propagated Plants on Lattice Space.

Many clonal plants have two reproductive patterns, seed propagation and vegetative propagation. By vegetative propagation, plants reproduce the genetically identical offspring with a low mortality, because resources are supplied from the other individuals through interconnected ramets at vegetative-propagated offspring. However, the ramets transport not only resources but also systemic pathogen. Pathogens evolve to establish and spread widely within the plant population. The superinfection, which is defined as the ability that an established pathogen spreads widely by infecting to already-infected individuals with other strains of a pathogen, is important to the evolution of pathogens. We examine the dynamics of plant reproduction and pathogen propagation considering spatial structure and the effect of superinfection on genetic diversity of pathogen by analysis of several models, 1-strain and multiple-strain models, on two-dimensional square lattice. In the analysis of 1-strain model, we derive equilibrium value by mean-field approximation and pair approximation, and its local stability by Routh-Hurwitz stability criterion. In the multiple-strain models, we analyze the dynamics by numerical simulation of mean-field approximation, pair approximation and Monte Carlo simulation. Through the analyses, we show the effect of parameter values to dynamics of models, such as transition of dominant strain of pathogen, competition between plants and pathogens and density of individuals. As a result, (i) The strain with intermediate cost becomes dominant when both superinfection rate and growth rate are low. (ii) The competition between plants and pathogens occurs in the phase of coexistence of various strains by pair approximation and Monte Carlo simulation. (iii) Too high growth rate leads to the decrease of plant population in all models. (iv) Pathogens are easy to maintain their genetic diversity with low superinfection rate. However, if they do not superinfect, the maintenance becomes difficult. (v) When growth rate of plant is low, individuals are very influenced by distant individuals.

Durable coexistence of donor and recipient strains after fecal microbiota transplantation.

Fecal microbiota transplantation (FMT) has shown efficacy in treating recurrent Clostridium difficile infection and is increasingly being applied to other gastrointestinal disorders, yet the fate of native and introduced microbial strains remains largely unknown. To quantify the extent of donor microbiota colonization, we monitored strain populations in fecal samples from a recent FMT study on metabolic syndrome patients using single-nucleotide variants in metagenomes. We found extensive coexistence of donor and recipient strains, persisting 3 months after treatment. Colonization success was greater for conspecific strains than for new species, the latter falling within fluctuation levels observed in healthy individuals over a similar time frame. Furthermore, same-donor recipients displayed varying degrees of microbiota transfer, indicating individual patterns of microbiome resistance and donor-recipient compatibilities.

A Novel HIV-1 Second-Generation Recombinant Form (CRF01_AE/07_BC) Among Heterosexuals in Nei Monggoi Autonomous Region in China.

Increasing second-generation recombinant forms (CRF01_AE/07_BC) have been detected in China recently. Here, we isolated a novel CRF01_AE/07_BC second-generation recombinant form in HIV-1-positive Nei Monggoi's heterosexuals with one CRF07_BC inserted into the CRF01_AE backbone. Polygenetic analyses showed that the CRF01_AE region was grouped with the previously reported cluster 5 lineage, which spreads among the sexual population in north of China, inferring that this recombinant event occurred through heterosexual contact in the north of China possibly. The growing emergence of recombinant forms means coexistence of multiple strains and complexity of the HIV-1 epidemic, which reminds us of the urgent necessity to focus the HIV surveillance among the high-risk populations nationwide in China, particularly to enhance preventive measures in HIV-1 low-prevalence areas.

The evolution of plant virus transmission pathways

The evolution of plant virus transmission pathways is studied through transmission via seed, pollen, or a vector. We address the questions: under what circumstances does vector transmission make pollen transmission redundant? Can evolution lead to the coexistence of multiple virus transmission pathways? We restrict the analysis to an annual plant population in which reproduction through seed is obligatory. A semi-discrete model with pollen, seed, and vector transmission is formulated to investigate these questions. We assume vector and pollen transmission rates are frequency-dependent and density-dependent, respectively. An ecological stability analysis is performed for the semi-discrete model and used to inform an evolutionary study of trade-offs between pollen and seed versus vector transmission. Evolutionary dynamics critically depend on the shape of the trade-off functions. Assuming a trade-off between pollen and vector transmission, evolution either leads to an evolutionarily stable mix of pollen and vector transmission (concave trade-off) or there is evolutionary bi-stability (convex trade-off); the presence of pollen transmission may prevent evolution of vector transmission. Considering a trade-off between seed and vector transmission, evolutionary branching and the subsequent coexistence of pollen-borne and vector-borne strains is possible. This study contributes to the theory behind the diversity of plant–virus transmission patterns observed in nature.

Glycan cross-feeding activities between bifidobacteria under in vitro conditions.

Bifidobacteria colonize the gut of various mammals, including humans, where they may metabolize complex, diet-, and host-derived carbohydrates. The glycan-associated metabolic features encoded by bifidobacteria are believed to be strongly influenced by cross-feeding activities due to the co-existence of strains with different glycan-degrading properties. In this study, we observed an enhanced growth yield of Bifidobacterium bifidum PRL2010 when co-cultivated with Bifidobacterium breve 12L, Bifidobacterium adolescentis 22L, or Bifidobacterium thermophilum JCM1207. This enhanced growth phenomenon was confirmed by whole genome transcriptome analyses, which revealed co-cultivation-associated transcriptional induction of PRL2010 genes involved in carbohydrate metabolism, such as those encoding for carbohydrate transporters and associated energy production, and genes required for translation, ribosomal structure, and biogenesis, thus supporting the idea that co-cultivation of certain bifidobacterial strains with B. bifidum PRL2010 causes enhanced metabolic activity, and consequently increased lactate and/or acetate production. Overall, these data suggest that PRL2010 cells benefit from the presence of other bifidobacterial strains.

Mutual Cross-Feeding Interactions between Bifidobacterium longum subsp. longum NCC2705 and Eubacterium rectale ATCC 33656 Explain the Bifidogenic and Butyrogenic Effects of Arabinoxylan Oligosaccharides.

Arabinoxylan oligosaccharides (AXOS) are a promising class of prebiotics that have the potential to stimulate the growth of bifidobacteria and the production of butyrate in the human colon, known as the bifidogenic and butyrogenic effects, respectively. Although these dual effects of AXOS are considered beneficial for human health, their underlying mechanisms are still far from being understood. Therefore, this study investigated the metabolic interactions between Bifidobacterium longum subsp. longum NCC2705 (B. longum NCC2705), an acetate producer and arabinose substituent degrader of AXOS, and Eubacterium rectale ATCC 33656, an acetate-converting butyrate producer. Both strains belong to prevalent species of the human colon microbiota. The strains were grown on AXOS during mono- and coculture fermentations, and their growth, AXOS consumption, metabolite production, and expression of key genes were monitored. The results showed that the growth of both strains and gene expression in both strains were affected by cocultivation and that these effects could be linked to changes in carbohydrate consumption and concomitant metabolite production. The consumption of the arabinose substituents of AXOS by B. longum NCC2705 with the concomitant production of acetate allowed E. rectale ATCC 33656 to produce butyrate (by means of a butyryl coenzyme A [CoA]:acetate CoA-transferase), explaining the butyrogenic effect of AXOS. Eubacterium rectale ATCC 33656 released xylose from the AXOS substrate, which favored the B. longum NCC2705 production of acetate, explaining the bifidogenic effect of AXOS. Hence, those interactions represent mutual cross-feeding mechanisms that favor the coexistence of bifidobacterial strains and butyrate producers in the same ecological niche. In conclusion, this study provides new insights into the bifidogenic and butyrogenic effects of AXOS.

Host switching vs. host sharing in overlapping sylvatic Trypanosoma cruzi transmission cycles

ABSTRACTThe principle of competitive exclusion is well established for multiple populations competing for the same resource, and simple models for multistrain infection exhibit it as well when cross-immunity precludes coinfections. However, multiple hosts provide niches for different pathogens to occupy simultaneously. This is the case for the vector-borne parasite Trypanosoma cruzi in overlapping sylvatic transmission cycles in the Americas, where it is enzootic. This study uses cycles in the USA involving two different hosts but the same vector species as a context for the study of the mechanisms behind the communication between the two cycles. Vectors dispersing in search of new hosts may be considered to move between the two cycles (host switching) or, more simply, to divide their time between the two host types (host sharing). Analysis considers host switching as an intermediate case between isolated cycles and intermingled cycles (host sharing) in order to examine the role played by the host-switching rate in permitting coexistence of multiple strains in a single-host population. Results show that although the population dynamics (demographic equilibria) in host-switching models align well with those in the limiting models (host sharing or isolated cycles), infection dynamics differ significantly, in ways that sometimes illuminate the underlying epidemiology (such as differing host susceptibilities to infection) and sometimes reveal model limitations (such as host switching dominating the infection dynamics). Numerical work suggests that the model explains the trace presence of TcI in raccoons but not the more significant co-persistence observed in woodrats.

Host-plant dependent population genetics of the invading weevil Hypera postica.

Population genetics of invading pests can be informative for understanding their ecology. In this study, we investigated population genetics of the invasive alfalfa weevil Hypera postica in Fukuoka Prefecture, Japan. We analyzed mitochondrial tRNALeu-COII, nuclear EF-1α gene fragments, and Wolbachia infection in relation to three leguminous host plants: Vicia angustifolia, Vicia villosa, and a new host Astragalus sinicus cultivated as a honey source and green manure crop. A parsimony network generated from mitochondrial gene sequences uncovered two major haplotypic groups, Western and Egyptian. In contrast to reported Wolbachia infection of the Western strain in the United States, none of our analyzed individuals were infected. The absence of Wolbachia may contribute to the stable coexistence of mitochondrial strains through inter-strain reproductive compatibility. Hypera postica genetic variants for the mitochondrial and nuclear genes were associated neither with host plant species nor with two geographic regions (Hisayama and Kama) within Fukuoka. Mitochondrial haplogroups were incongruent with nuclear genetic variants. Genetic diversity at the nuclear locus was the highest for the populations feeding on V. angustifolia. The nuclear data for A. sinicus-feeding populations indicated past sudden population growth and extended Bayesian skyline plot analysis based on the mitochondrial and nuclear data showed that the growth of A. sinicus-feeding population took place within the past 1000 years. These results suggest a shorter history of A. sinicus as a host plant compared with V. angustifolia and a recent rapid growth of H. postica population using the new host A. sinicus.

Trade-offs between and within scales: environmental persistence and within-host fitness of avian influenza viruses.

Trade-offs between different components of a pathogen's replication and transmission cycle are thought to be common. A number of studies have identified trade-offs that emerge across scales, reflecting the tension between strategies that optimize within-host proliferation and large-scale population spread. Most of these studies are theoretical in nature, with direct experimental tests of such cross-scale trade-offs still rare. Here, we report an analysis of avian influenza A viruses across scales, focusing on the phenotype of temperature-dependent viral persistence. Taking advantage of a unique dataset that reports both environmental virus decay rates and strain-specific viral kinetics from duck challenge experiments, we show that the temperature-dependent environmental decay rate of a strain does not impact within-host virus load. Hence, for this phenotype, the scales of within-host infection dynamics and between-host environmental persistence do not seem to interact: viral fitness may be optimized on each scale without cross-scale trade-offs. Instead, we confirm the existence of a temperature-dependent persistence trade-off on a single scale, with some strains favouring environmental persistence in water at low temperatures while others reduce sensitivity to increasing temperatures. We show that this temperature-dependent trade-off is a robust phenomenon and does not depend on the details of data analysis. Our findings suggest that viruses might employ different environmental persistence strategies, which facilitates the coexistence of diverse strains in ecological niches. We conclude that a better understanding of the transmission and evolutionary dynamics of influenza A viruses probably requires empirical information regarding both within-host dynamics and environmental traits, integrated within a combined ecological and within-host framework.

Quantifying the effects of the division of labor in metabolic pathways

Division of labor is commonly observed in nature. There are several theories that suggest diversification in a microbial community may enhance stability and robustness, decrease concentration of inhibitory intermediates, and increase efficiency. Theoretical studies to date have focused on proving when the stable co-existence of multiple strains occurs, but have not investigated the productivity or biomass production of these systems when compared to a single ‘super microbe’ which has the same metabolic capacity. In this work we prove that if there is no change in the growth kinetics or yield of the metabolic pathways when the metabolism is specialized into two separate microbes, the biomass (and productivity) of a binary consortia system is always less than that of the equivalent monoculture. Using a specific example of Escherichia coli growing on a glucose substrate, we find that increasing the growth rates or substrate affinities of the pathways is not sufficient to explain the experimentally observed productivity increase in a community. An increase in pathway efficiency (yield) in specialized organisms provides the best explanation of the observed increase in productivity.

Coexistence of multiple strains of porcine parvovirus 2 in pig farms.

The porcine parvovirus 2 (PPV2) genome was first identified in 2001 in Myanmar. Recently, the PPV2 genome has been found in several other countries. In this study, the prevalence of PPV2 in Japanese domestic pigs was investigated and found to be 58% (69/120) in healthy domestic pigs and 100% (69/69) in sick domestic pigs. Sequencing and phylogenetic analysis of the PCR products of the VP1 gene and an almost full length PPV2 clone indicated that diverged PPV2 strains exist in Japan. Clearly distinct strains of PPV2 were detected in 7 of the 10 pig farms.

Population interaction structure and the coexistence of bacterial strains playing ‘rock–paper–scissors’

The simplest example of non‐transitive competition is the game rock–paper–scissors (RPS), which exhibits characteristic cyclic strategy replacement: paper beats rock, which in turn beats scissors, which in turn beats paper. In addition to its familiar use in understanding human decision‐making, rock–paper–scissors is also played in many biological systems. Among other reasons, this is important because it potentially provides a mechanism whereby species‐ or strain coexistence can occur in the face of intense competition. Kerr et al. (2002, Nature 418: 171–174) use complementary experiments and simulations to show that RPS‐playing toxic, resistant, and susceptible E. coli bacteria can coexist when interactions between the strains are spatially explicit. This raises the question of whether limited interactions associated with space are sufficient to allow strain coexistence, or whether space per se is crucial. I approach this question by extending the Kerr et al. model to include different (aspatial) population network structures with the same degree distributions as corresponding spatial lattice models. I show that the coexistence that occurs for some parameter combinations when simulated bacterial strains compete on lattices is absent when they compete on random regular graphs. Further, considering small‐world networks of intermediate ‘quenched randomness’ between lattices and random regular graphs, I show that only small deviations from pure spatial interactions are sufficient to prevent strain coexistence. These results emphasize the explicit role of space, rather than merely limited interactions, as being decisive in allowing the coexistence of toxic, resistant, and susceptible strains in this model system.

Morphological plasticity of Streptococcus oralis isolates for biofilm production, invasiveness, and architectural patterns

ObjectiveStreptococcus oralis is an early coloniser of the oral cavity that contributes to dental plaque formation. Many different genotypes can coexist in the same individual and cause opportunistic infections such as bacterial endocarditis. However, little is known about virulence factors involved in those processes. The aim was to analyze the evolving growth of S. oralis colony/biofilm to find out potentially pathogenic features. DesignThirty-three S. oralis isolates were analyzed for: (1) biofilm production, by spectrophotometric microtiter plate assay; (2) colonial internal architecture, by histological methods and light and electron microscopy; (3) agar invasion, by a new colony-biofilm assay. ResultsS. oralis colonies showed two different growth patterns: (1) fast growth rate without invasion or minimally invasive; (2) slow growth rate, but high invasion ability. 12.1% of strains were biofilm non-producers and 24.2% not invasive, compared to 51.5% biofilm high-producers and 39.4% very invasive. Both phenotypic characteristics tended to be mutually exclusive. However, a limited number of strains (15%) co-expressed these features at the highest level. ConclusionsMorphological plasticity of S. oralis highlighted in this study may have important ecological and clinical implications. Coexistence of strains with different growth patterns could produce a synergic effect in the formation and development of subgingival dental plaque. Moreover, invasiveness might regulate dissemination and colonisation mechanisms. Simultaneous co-expression of high-invasive and high-biofilm phenotypes gives a fitness advantage during colonisation and may confer higher pathogenic potential.