Three live vaccine candidates of Salmonella enterica subspecies I serotype Abortusovis (aroA, cya crp cdt, and plasmid-cured strains) have been developed, and their efficacies in inducing humoral ...antibodies and protecting against abortion after challenge with wild-type strain SS44 were evaluated in sheep. Following estrus synchronization, animals were immunized 3 weeks after fertilization and boosted once 3 weeks later. Following challenge with wild-type SS44, pregnancy failure of vaccinated ewes was reduced compared to that of nonimmunized controls. Attenuation of each vaccine was also assessed in challenge experiments with nonimmunized pregnant ewes and in BALB/c mice. All three vaccine candidates appear to be safe for use in sheep and provide a model for the development of live vaccine candidates against naturally occurring ovine salmonellosis.
Bacterial flagella are potent immunogens and aromatic-dependent (aro) Salmonella as live vaccines evoke humoral and cellular immune responses. Such strains expressing epitopes of protective antigens ...as inserts in flagellin would provide a novel way to vaccinate against diseases caused by unrelated pathogens. A synthetic oligonucleotide specifying an epitope of cholera toxin subunit B was inserted in a Salmonella flagellin gene. The chimeric flagellin functioned normally and the epitope was expressed at the flagellar surface. Parenteral administration to mice of an aroA flagellin-negative strain of S. dublin expressing the chimeric flagellin gene evoked antibody to cholera toxin.
Land ecosystems sequester on average about a quarter of anthropogenic CO2 emissions. It has been proposed that nitrogen (N) availability will exert an increasingly limiting effect on plants’ ability ...to store additional carbon (C) under rising CO2, but these mechanisms are not well understood. Here, we review findings from elevated CO2 experiments using a plant economics framework, highlighting how ecosystem responses to elevated CO2 may depend on the costs and benefits of plant interactions with mycorrhizal fungi and symbiotic N-fixing microbes. We found that N-acquisition efficiency is positively correlated with leaf-level photosynthetic capacity and plant growth, and negatively with soil C storage. Plants that associate with ectomycorrhizal fungi and N-fixers may acquire N at a lower cost than plants associated with arbuscular mycorrhizal fungi. However, the additional growth in ectomycorrhizal plants is partly offset by decreases in soil C pools via priming. Collectively, our results indicate that predictive models aimed at quantifying C cycle feedbacks to global change may be improved by treating N as a resource that can be acquired by plants in exchange for energy, with different costs depending on plant interactions with microbial symbionts.
Terrestrial ecosystems remove about 30 per cent of the carbon dioxide (CO2) emitted by human activities each year1, yet the persistence ofthis carbon sink depends partly on how plant biomass and soil ...organic carbon (SOC) stocks respond to future increases in atmospheric CO2 (refs. 23). Although plant biomass often increases in elevated CO2 (eCO2) experiments4-6, SOC has been observed to increase, remain unchanged or even decline7. The mechanisms that drive this variation across experiments remain poorly understood, creating uncertainty in climate projections8,9. Here we synthesized data from 108 eCO2 experiments and found that the effect of eCO2 on SOC stocks is best explained by a negative relationship with plant biomass: when plant biomass is strongly stimulated by eCO2, SOC storage declines; conversely, when biomass is weakly stimulated, SOC storage increases. This trade-off appears to be related to plant nutrient acquisition, in which plants increase their biomass by mining the soil for nutrients, which decreases SOC storage. We found that, overall, SOC stocks increase with eCO2 in grasslands (8 ± 2 per cent) but not in forests (0 ± 2 per cent), even though plant biomass in grasslands increase less (9 ± 3 per cent) than in forests (23 ± 2 per cent). Ecosystem models do not reproduce this trade-off, which implies that projections of SOC may need to be revised.
Up to 80% of faecal Escherichia coli strains are able to produce type 1 pili. These filamentous bacterial surface organelles, which mediate mannose-sensitive attachment to mammalian epithelial cells, ...are also conserved throughout the Enterobacteriaceae. As a potential explanation for their prevalence among intestinal isolates of enteric bacteria, it has been widely speculated that type 1 pili are important for adherence to the host's intestinal mucosa. However, conclusive evidence for this idea is lacking, and there are reasonable grounds for doubting such an effect. Permanent interruption of type 1 piliation in previously pil+ E. coli (by directed mutagenesis of pilA, the gene coding for the major structural subunit of type 1 pili) does not diminish the density of intestinal colonization in individual animals. Rather, as we demonstrate here, this lesion results in a dramatic decrease in transmission of E. coli K1 from experimentally colonized neonatal rats to their littermates. The enhanced communicability associated with type 1 piliation suggests a heretofore unrecognized explanation for the prevalence of type 1 pili among intestinal E. coli; one that does not necessarily require the direct action of these organelles at the intestinal mucosa.
Contents Summary 507 I. Introduction 507 II. The return on investment approach 508 III. CO
response spectrum 510 IV. Discussion 516 Acknowledgements 518 References 518 SUMMARY: Land ecosystems ...sequester on average about a quarter of anthropogenic CO
emissions. It has been proposed that nitrogen (N) availability will exert an increasingly limiting effect on plants' ability to store additional carbon (C) under rising CO
, but these mechanisms are not well understood. Here, we review findings from elevated CO
experiments using a plant economics framework, highlighting how ecosystem responses to elevated CO
may depend on the costs and benefits of plant interactions with mycorrhizal fungi and symbiotic N-fixing microbes. We found that N-acquisition efficiency is positively correlated with leaf-level photosynthetic capacity and plant growth, and negatively with soil C storage. Plants that associate with ectomycorrhizal fungi and N-fixers may acquire N at a lower cost than plants associated with arbuscular mycorrhizal fungi. However, the additional growth in ectomycorrhizal plants is partly offset by decreases in soil C pools via priming. Collectively, our results indicate that predictive models aimed at quantifying C cycle feedbacks to global change may be improved by treating N as a resource that can be acquired by plants in exchange for energy, with different costs depending on plant interactions with microbial symbionts.
Norby et al center their critique on the design of the data set and the response variable used. We address these criticisms and reinforce the conclusion that plants that associate with ...ectomycorrhizal fungi exhibit larger biomass and growth responses to elevated CO
compared with plants that associate with arbuscular mycorrhizae.
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