Thiamethoxam soil contaminations reduce fertility of soil-dwelling beetles, Aethina tumida.

There in increasing evidence for recent global insect declines. This is of major concern as insects play a critical role in ecosystem functionality and human food security. Even though environmental pollutants are known to reduce insect fertility, their potential effects on insect fitness remain poorly understood - especially for soil-dwelling species. Here, we show that fertility of soil-dwelling beetles, Aethina tumida, is reduced, on average, by half due to field-realistic neonicotinoid soil contaminations. In the laboratory, pupating beetles were exposed via soil to concentrations of the neonicotinoid thiamethoxam that reflect global pollution of agricultural and natural habitats. Emerged adult phenotypes and reproduction were measured, and even the lowest concentration reported from natural habitats reduced subsequent reproduction by 50%. The data are most likely a conservative estimate as the beetles were only exposed during pupation. Since the tested concentrations reflect ubiquitous soil pollution, the data reveal a plausible mechanism for ongoing insect declines. An immediate reduction in environmental pollutants is urgently required if our aim is to mitigate the prevailing loss of species biodiversity.

Improved methods to assess the effect of bacteria on germination of fungal spores.

Bacterial-fungal interactions (BFI) play a major role on ecosystem functioning and might be particularly relevant at a specific development stage. For instance, in the case of biological control of fungal pathogens by bacteria, a highly relevant kind of BFI, in-vitro experiments often assess the impact of a bacterium on the inhibition of actively growing mycelia. However, this fails to consider other stages of plant infection such as the germination of a spore or a sclerotium. This study aims to present novel experimental platforms for in-vitro experiments with fungal spores, in order to assess the effect of bacteria on germination and fungal growth control, to recover the metabolites produced in the interaction, and to enhance direct visualisation of BFI. Botrytis cinerea, a phytopathogenic fungus producing oxalic acid (OA) as pathogenicity factor, was used as model. Given that oxalotrophic bacteria have been shown previously to control the growth of B. cinerea, the oxalotrophic bacteria Cupriavidus necator and Cupriavidus oxalaticus were used as models. The experiments performed demonstrated the suitability of the methods and confirmed that both bacteria were able to control the growth of B. cinerea, but only in media in which soluble OA was detected by the fungus. The methods presented here can be easily performed in any microbiology laboratory and are not only applicable to screen for potential biocontrol agents, but also to better understand BFI.

Regulatory and Functional Aspects of Indolic Metabolism in Plant Systemic Acquired Resistance.

Tryptophan-derived, indolic metabolites possess diverse functions in Arabidopsis innate immunity to microbial pathogen infection. Here, we investigate the functional role and regulatory characteristics of indolic metabolism in Arabidopsis systemic acquired resistance (SAR) triggered by the bacterial pathogen Pseudomonas syringae. Indolic metabolism is broadly activated in both P. syringae-inoculated and distant, non-inoculated leaves. At inoculation sites, camalexin, indol-3-ylmethylamine (I3A), and indole-3-carboxylic acid (ICA) are the major accumulating compounds. Camalexin accumulation is positively affected by MYB122, and the cytochrome P450 genes CYP81F1 and CYP81F2. Local I3A production, by contrast, occurs via indole glucosinolate breakdown by PEN2- dependent and independent pathways. Moreover, exogenous application of the defense hormone salicylic acid stimulates I3A generation at the expense of its precursor indol-3-ylmethylglucosinolate (I3M), and the SAR regulator pipecolic acid primes plants for enhanced P. syringae-induced activation of distinct branches of indolic metabolism. In uninfected systemic tissue, the metabolic response is more specific and associated with enhanced levels of the indolics I3A, ICA, and indole-3-carbaldehyde (ICC). Systemic indole accumulation fully depends on functional CYP79B2/3, PEN2, and MYB34/51/122, and requires functional SAR signaling. Genetic analyses suggest that systemically elevated indoles are dispensable for SAR and associated systemic increases of salicylic acid. However, soil-grown but not hydroponically -cultivated cyp79b2/3 and pen2 plants, both defective in indolic secondary metabolism, exhibit pre-induced immunity, which abrogates their intrinsic ability to induce SAR.