Establishment and impact of insect agents deployed for the biological control of invasive Asteraceae: prospects for the control of <Emphasis Type="Italic">Senecio madagascariensis</Emphasis>

Several invasive Asteraceae have been targeted for biological control worldwide, with variable success. Senecio madagascariensis Poiret, which invades agricultural lands in Australia and Hawaii, is a recent target. Since several potential insect agents were recorded in the plant’s native range in South Africa, we assessed biocontrol efforts against asteraceous weeds to determine those most likely to deliver success. Some 108 insect species, from five orders and 23 families, were deployed against 38 weed taxa, mostly in the mainland USA, Canada, Australia and New Zealand. Coleoptera (mainly Curculionidae and Chrysomelidae), Diptera (Tephritidae) and Lepidoptera (Tortricidae) featured the most. Despite high establishment success (73% of releases across countries), only 37% of successful releases achieved meaningful impact. Although root-feeding and stem-feeding insects appeared to be the best candidates, neither insect family nor feeding guild significantly influenced the probability of success. This synthesis of the global contribution of different guilds of specialist herbivores to the management of invasive Asteraceae is guiding the selection of candidate agents for the biocontrol of S. madagascariensis in Australia.     

Community Analysis of Ammonia and Nitrite Oxidizers during Start-Up of Nitritation Reactors

Partial nitrification of ammonium to nitrite under oxic conditions (nitritation) is a critical process for the effective use of alternative nitrogen removal technologies from wastewater. Here we investigated the conditions which promote establishment of a suitable microbial community for performing nitritation when starting from regular sewage sludge. Reactors were operated in duplicate under different conditions (pH, temperature, and dilution rate) and were fed with 50 mM ammonium either as synthetic medium or as sludge digester supernatant. In all cases, stable nitritation could be achieved within 10 to 20 days after inoculation. Quantitative in situ hybridization analysis with group-specific fluorescent rRNA-targeted oligonucleotides (FISH) in the different reactors showed that nitrite-oxidizing bacteria of the genus Nitrospira were only active directly after inoculation with sewage sludge (up to 4 days and detectable up to 10 days). As demonstrated by quantitative FISH and restriction fragment length polymorphism (RFLP) analyses of the amoA gene (encoding the active-site subunit of the ammonium monooxygenase), the community of ammonia-oxidizing bacteria changed within the first 15 to 20 days from a more diverse set of populations consisting of members of the Nitrosomonas communis and Nitrosomonas oligotropha sublineages and the Nitrosomonas europaea-Nitrosomonas eutropha subgroup in the inoculated sludge to a smaller subset in the reactors. Reactors operated at 30°C and pH 7.5 contained reproducibly homogeneous communities dominated by one amoA RFLP type from the N. europaea-N. eutropha group. Duplicate reactors at pH 7.0 developed into diverse communities and showed transient population changes even within the ammonia oxidizer community. Reactors at pH 7.5 and 25°C formed communities that were indistinguishable by the applied FISH probes but differing in amoA RFLP types. Communities in reactors fed with sludge digester supernatant exhibited a higher diversity and were constantly reinoculated with ammonium oxidizers from the supernatant. Therefore, such systems could be maintained at a higher dilution rate (0.75 day⁻¹ compared to 0.2 day⁻¹ for the synthetic wastewater reactors). Despite similar reactor performance with respect to chemical parameters, the underlying community structures were different, which may have an influence on stability during perturbations.     

Model-based inference of neutralizing antibody avidities against influenza virus

To assess the response to vaccination, quantity (concentration) and quality (avidity) of neutralizing antibodies are the most important parameters. Specifically, an increase in avidity indicates germinal center formation, which is required for establishing long-term protection. For influenza, the classical hemagglutination inhibition (HI) assay, however, quantifies a combination of both, and to separately determine avidity requires high experimental effort. We developed from first principles a biophysical model of hemagglutination inhibition to infer IgG antibody avidities from measured HI titers and IgG concentrations. The model accurately describes the relationship between neutralizing antibody concentration/avidity and HI titer, and explains quantitative aspects of the HI assay, such as robustness to pipetting errors and detection limit. We applied our model to infer avidities against the pandemic 2009 H1N1 influenza virus in vaccinated patients (n = 45) after hematopoietic stem cell transplantation (HSCT) and validated our results with independent avidity measurements using an enzyme-linked immunosorbent assay with urea elution. Avidities inferred by the model correlated with experimentally determined avidities (ρ = 0.54, 95% CI = [0.31, 0.70], P < 10⁻⁴). The model predicted that increases in IgG concentration mainly contribute to the observed HI titer increases in HSCT patients and that immunosuppressive treatment is associated with lower baseline avidities. Since our approach requires only easy-to-establish measurements as input, we anticipate that it will help to disentangle causes for poor vaccination outcomes also in larger patient populations. This study demonstrates that biophysical modelling can provide quantitative insights into agglutination assays and complement experimental measurements to refine antibody response analyses.     

Cryo neutron crystallography demonstrates influence of RNA 2′-OH orientation on conformation,sugar pucker and water structure

The ribose 2′-hydroxyl is the key chemical difference between RNA and DNA and primary source of their divergent structural and functional characteristics. Macromolecular X-ray diffraction experiments typically do not reveal the positions of hydrogen atoms. Thus, standard crystallography cannot determine 2′-OH orientation (H2′-C2′-O2′-HO2′ torsion angle) and its potential roles in sculpting the RNA backbone and the expansive fold space. Here, we report the first neutron crystal structure of an RNA, the Escherichia coli rRNA Sarcin-Ricin Loop (SRL). 2′-OD orientations were established for all 27 residues and revealed O-D bonds pointing toward backbone (O3′, 13 observations), nucleobase (11) or sugar (3). Most riboses in the SRL stem region show a 2′-OD backbone-orientation. GAGA-tetraloop riboses display a 2′-OD base-orientation. An atypical C2′-endo sugar pucker is strictly correlated with a 2′-OD sugar-orientation. Neutrons reveal the strong preference of the 2′-OH to donate in H-bonds and that 2′-OH orientation affects both backbone geometry and ribose pucker. We discuss 2′-OH and water molecule orientations in the SRL neutron structure and compare with results from a solution phase 10 μs MD simulation. We demonstrate that joint cryo-neutron/X-ray crystallography offers an all-in-one approach to determine the complete structural properties of RNA, i.e. geometry, conformation, protonation state and hydration structure.     

Environmental fate and microbial degradation of aminopolycarboxylic acids

Aminopolycarboxylic acids (APCAs) have the ability to form stable, water-soluble complexes with di- and trivalent metal ions. For that reason, synthetic APCAs are used in a broad range of domestic products and industrial applications to control solubility and precipitation of metal ions. Because most of these applications are water-based, APCAs are disposed of in wastewater and reach thus sewage treatment plants and the environment, where they undergo abiotic and/or biotic degradation processes. Recently, also natural APCAs have been described which are produced by plants or micro-organisms and are involved in the metal uptake by these organisms. For the two most widely used APCAs, nitrilotriacetate (NTA) and ethylenediaminetetraacetate (EDTA), transformation and mineralisation processes have been studied rather well, while for other xenobiotic APCAs and for the naturally occurring APCAs little is known on their fate in the environment. Whereas NTA is mainly degraded by bacteria under both oxic and anoxic conditions, biodegradation is apparently of minor importance for the environmental fate of EDTA. Photodegradation of iron(III)-complexed EDTA is supposed to be mostly responsible for its elimination. Isolation of a number of NTA- and EDTA-utilising bacterial strains has been reported and the spectrum of APCAs utilised by the different isolates indicates that some of them are able to utilise a range of different APCAs whereas others seem to be restricted to one compound. The two best characterised obligately aerobic NTA-utilising genera (Chelatobacter and Chelatococcus) are members of the alpha-subgroup of Proteobacteria. There is good evidence that they are present in fairly high numbers in surface waters, soils and sewage treatment plants. The key enzymes involved in NTA degradation in Chelatobacter and Chelatococcus have been isolated and characterised. The two first catabolic steps are catalysed by a monooxygenase (NTA MO) and a membrane-bound iminodiacetate dehydrogenase. NTA MO has been cloned and sequenced and its regulation as a function of growth conditions has been studied. Under denitrifying conditions, NTA catabolism is catalysed by a NTA dehydrogenase. EDTA breakdown was found to be initiated by a MO also which shares many characteristics with NTA MO from strictly aerobic NTA-degrading bacteria. In contrast, degradation of [S,S]-ethylenediaminedisuccinate ([S,S]-EDDS), a structural isomer of EDTA, was shown to be catalysed by an EDDS lyase in both an EDTA degrader and in a NTA-utilising Chelatococcus strain. So far, transport of APCAs into cells has only been studied for EDTA and the results obtained give strong evidence for an energy-dependent carrier system and Ca(2+) seems to be co-transported with EDTA. Due to their metal-complexing capacities, APCAs occur in the environment mostly in the metal-complexed form. Hence, the influence of metal speciation on various degradation processes is of utmost importance to understand the environmental behaviour of these compounds. In case of biodegradation, the effect of metal speciation is rather difficult to assess at the whole cell level and therefore only limited good data are available. In contrast, the influence of metal speciation on the intracellular enzymatic breakdown of APCAs is rather well documented but no generalising pattern applicable to all enzymes was found.     

Control of soil pH on turnover of belowground organic matter in subalpine grassland

Grasslands store substantial amounts of carbon in the form of organic matter in soil and roots. At high latitudes and elevation, turnover of these materials is slow due to various interacting biotic and abiotic constraints. Reliable estimates on the future of belowground carbon storage in cold grassland soils thus require quantitative understanding of these factors. We studied carbon turnover of roots, labile coarse particulate organic matter (cPOM) and older non-cPOM along a natural pH gradient (3.9–5.9) in a subalpine grassland by utilizing soil fractionation and radiocarbon dating. Soil carbon stocks and root biomass, turnover, and decomposability did not scale with soil pH whereas mean residence times of both soil organic matter fractions significantly increased with declining pH. The effect was twice as strong for non-cPOM, which was also stronger enriched in ¹⁵N at low pH. Considering roots as important precursors for cPOM, the weaker soil pH effect on cPOM turnover may have been driven by comparably high root pH values. At pH < 5, long non-cPOM mean residence times were probably related to pH dependent changes in substrate availability. Differences in turnover along the pH gradient were not reflected in soil carbon stocks because aboveground productivity was lower under acidic conditions and, in turn, higher inputs from aboveground plant residues compensated for faster soil carbon turnover at less acidic pH. In summary, the study provides evidence for a strong and differential regulatory role of pH on the turnover of soil organic matter that needs consideration in studies aiming to quantify effects of changing environmental conditions on belowground carbon storage.     

Unraveling environmental drivers of a recent increase in Swiss fungi fruiting

Disentangling biotic and abiotic drivers of wild mushroom fruiting is fraught with difficulties because mycelial growth is hidden belowground, symbiotic and saprotrophic supply strategies may interact, and myco‐ecological observations are often either discontinuous or too short. Here, we compiled and analyzed 115 417 weekly fungal fruit body counts from permanent Swiss inventories between 1975 and 2006. Mushroom fruiting exhibited an average autumnal delay of 12 days after 1991 compared with before, the annual number of fruit bodies increased from 1801 to 5414 and the mean species richness doubled from 10 to 20. Intra‐ and interannual coherency of symbiotic and saprotrophic mushroom fruiting, together with little agreement between mycorrhizal yield and tree growth suggests direct climate controls on fruit body formation of both nutritional modes. Our results contradict a previously reported declining of mushroom harvests and propose rethinking the conceptual role of symbiotic pathways in fungi‐host interaction. Moreover, this conceptual advancement may foster new cross‐disciplinary research avenues, and stimulate questions about possible amplifications of the global carbon cycle, as enhanced fungal production in moist mid‐latitude forests rises carbon cycling and thus increases greenhouse gas exchanges between terrestrial ecosystems and the atmosphere.