Does wheat genetically modified for disease resistance affect root-colonizing pseudomonads and arbuscular mycorrhizal fungi?

This study aimed to evaluate the impact of genetically modified (GM) wheat with introduced pm3b mildew resistance transgene, on two types of root-colonizing microorganisms, namely pseudomonads and arbuscular mycorrhizal fungi (AMF). Our investigations were carried out in field trials over three field seasons and at two locations. Serial dilution in selective King's B medium and microscopy were used to assess the abundance of cultivable pseudomonads and AMF, respectively. We developed a denaturing gradient gel electrophoresis (DGGE) method to characterize the diversity of the pqqC gene, which is involved in Pseudomonas phosphate solubilization. A major result was that in the first field season Pseudomonas abundances and diversity on roots of GM pm3b lines, but also on non-GM sister lines were different from those of the parental lines and conventional wheat cultivars. This indicates a strong effect of the procedures by which these plants were created, as GM and sister lines were generated via tissue cultures and propagated in the greenhouse. Moreover, Pseudomonas population sizes and DGGE profiles varied considerably between individual GM lines with different genomic locations of the pm3b transgene. At individual time points, differences in Pseudomonas and AMF accumulation between GM and control lines were detected, but they were not consistent and much less pronounced than differences detected between young and old plants, different conventional wheat cultivars or at different locations and field seasons. Thus, we conclude that impacts of GM wheat on plant-beneficial root-colonizing microorganisms are minor and not of ecological importance. The cultivation-independent pqqC-DGGE approach proved to be a useful tool for monitoring the dynamics of Pseudomonas populations in a wheat field and even sensitive enough for detecting population responses to altered plant physiology.

Seasonality of Ixodes ricinus ticks on vegetation and on rodents and Borrelia burgdorferi sensu lato genospecies diversity in two Lyme borreliosis-endemic areas in Switzerland.

We compared Ixodes ricinus questing density, the infestation of rodents by immature stages, and the diversity of Borrelia burgdorferi sensu lato (sl) in questing ticks and ticks collected from rodents in two Lyme borreliosis (LB)-endemic areas in Switzerland (Portes-Rouges [PR] and Staatswald [SW]) from 2003 to 2005. There were variations in the seasonal pattern of questing tick densities among years. Questing nymphs were globally more abundant at PR than at SW, but the proportion of rodents infested by immature ticks was similar (59.4% and 61%, respectively). Questing tick activity lasted from February to November with a strong decline in June. The seasonal pattern of ticks infesting rodents was different. Ticks infested rodents without decline in summer, suggesting that the risk of being bitten by ticks remains high during the summer. Rodents from SW showed the highest infestation levels (10±21.6 for larvae and 0.54±1.65 for nymphs). The proportion of rodents infested simultaneously by larvae and nymphs (co-feeding ticks) was higher at SW (28%) than at PR (11%). Apodemus flavicollis was the species the most frequently infested by co-feeding ticks, and Myodes glareolus was the most infective rodent species as measured by xenodiagnosis. At PR, the prevalence of B. burgdorferi sl in questing ticks was higher (17.8% for nymphs and 32.4% for adults) than at SW (10.4% for nymphs and 24.8% for adults), with B. afzelii as the dominant species, but B. garinii, B. burgdorferi sensu stricto, and B. valaisiana were also detected. Rodents transmitted only B. afzelii (at PR and at SW) and B. bavariensis (at SW) to ticks, and no mixed infection by additional genospecies was observed in co-feeding ticks. This implies that co-feeding transmission does not contribute to genospecies diversity. However, persistent infections in rodents and co-feeding transmission contribute to the perpetuation of B. afzelii in nature.

Borrelia afzelii ospC genotype diversity in Ixodes ricinus questing ticks and ticks from rodents in two Lyme borreliosis endemic areas: contribution of co-feeding ticks.

In Europe, the Lyme borreliosis (LB) agents like Borrelia burgdorferi sensu stricto (ss), B. afzelii, and B. garinii are maintained in nature by enzoonotic transmission cycles between vertebrate hosts and Ixodes ricinus ticks. The outer surface protein C is a highly antigenic protein expressed by spirochaetes during transmission from ticks to mammals as well as during dissemination in the vertebrate hosts. Previous studies based on analysis of ospC gene sequences have led to the classification of ospC genotypes into ospC groups. The aim of this study was to analyse and compare ospC group distribution among isolates of the rodent-associated genospecies, B. afzelii, at 3 levels (questing ticks, ticks feeding on rodents, and xenodiagnostic ticks). Isolates were obtained during a study carried out in 2 LB endemic areas located on the Swiss Plateau [Portes-Rouges (PR) and Staatswald (SW)], where rodents were differently infested by co-feeding ticks (Pérez et al., unpublished data). Overall, we identified 10 different ospC groups with different distributions among isolates from questing ticks, ticks that detached from rodents, and xenodiagnostic ticks at the 2 sites. We observed a higher ospC diversity among isolates from ticks that fed on rodents at SW, and mixed infections with 2 ospC groups were also more frequent among isolates from ticks that fed on rodents at SW (n=18) than at PR (n=1). At both sites, B. afzelii isolates obtained from larvae that were feeding on the rodents simultaneously with nymphs displayed a higher diversity of ospC groups (mean number of ospC groups: 2.25 for PR and 1.75 for SW) than isolates from larvae feeding without nymphs (mean number of ospC groups: 1.17 for PR and 1 for SW). We suggest that co-feeding transmission of Borrelia, previously described in laboratory models, contributes in nature in promoting and maintaining ospC diversity within local tick populations.