Browsing by Subject "Metabolite"

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Hydroxylated transformation products obtained after UV irradiation of the current-use brominated flame retardants hexabromobenzene, pentabromotoluene, and pentabromoethylbenzene
(2023) Klimm, Alexandra; Vetter, Walter
Hexabromobenzene (HBB), pentabromotoluene (PBT), and pentabromoethylbenzene (PBEB) are current-use brominated flame retardants (cuBFRs) which have been repeatedly detected in environmental samples. Since information on hydroxylated transformation products (OH-TPs) was scarcely available, the three polybrominated compounds were UV irradiated for 10 min in benzotrifluoride. Fractionation on silica gel enabled the separate collection and identification of OH-TPs. For more insights, aliquots of the separated OH-TPs were UV irradiated for another 50 min (60 min total UV irradiation time). The present investigation of polar UV irradiation products of HBB, PBT, and PBEB was successful in each case. Altogether, eight bromophenols were detected in the case of HBB (three Br3-, four Br4-, and one Br5-isomer), and nine OH-TPs were observed in the case of PBT/PBEB (six Br3- and three Br4-congeners). In either case, Br➔OH exchange was more relevant than H➔OH exchange. Also, such exchange was most relevant in meta- and ortho-positions. As a further point, and in agreement with other studies, the transformation rate decreased with decreasing degree of bromination. UV irradiation of HBB additionally resulted in the formation of tri- and tetrabrominated dihydroxylated compounds (brominated diphenols) that were subsequently identified. These dihydroxylated transformation products were found to be more stable than OH-TPs.
Unveiling the plant-associated microbiome responses and nitrification inhibition aspects of perennial intermediate wheatgrass (Thinopyrum intermedium)
(2025) Issifu, Sulemana; Rasche, Frank
Perennialization of agriculture has recently garnered attention as a nature-based solution (NBS) to complement predominantly annual cropping systems, offering a pathway toward sustainable agriculture and enhanced protection of agroecosystems. In this regard, the perennial intermediate wheatgrass, Thinopyrum intermedium, trade name Kernza®, has been proposed as a model plant for achieving perennialization of cereal cropping systems. Kernza® provides a broad range of ecosystem services, including enhanced carbon sequestration, enhanced biodiversity, and regulation of the nitrogen (N) cycle. Some studies reported regulated nitrification in Kernza® fields through reduced N2O emissions, low N leaching, and high legacy N. These traits indicate a plant-exerted control of nitrification through the secretion of bioactive metabolites, a concept known as biological nitrification inhibition (BNI). However, no study had investigated the mechanism behind these BNI traits of Kernza®. Relatedly, existing BNI studies have largely been confined to the identification and testing of single and novel metabolites. Moreover, while some studies have reported the ability of Kernza® to stimulate microbial activity and enhance microbial diversity, there is currently no study in a European context on the potential influence of Kernza® on the rhizosphere microbiome. Thus, this doctoral study aimed to fill these knowledge gaps. The first study used a metabolome fingerprinting approach to profile the metabolome of the Kernza® biomass collected from the field and root exudates collected under N sources (ammonium (NH4+) versus nitrate (NO3-)) in a hydroponic system. Multiple nitrification inhibitors, including several phenolic metabolites, were identified in higher quantities in the biomass of Kernza® than in annual wheat. These metabolites were also concurrently exuded in higher quantities by the roots of Kernza® under NH4+-N source than NO3--N source. Bioassays involving multiple ammonia-oxidising bacteria and archaea (AOB and AOA) confirmed the antimicrobial properties of crude root exudates of Kernza®, as well as individual metabolites such as caffeic acid, vanillic acid, vanillin, and phenylalanine. Soil incubation experiments further demonstrated the nitrification inhibition potential of all tested metabolites, except phenylalanine. This study presents the initial evidence elucidating the mechanisms by which Kernza® regulates nitrification and clarifies the function of Kernza’s® metabolome in mediating nitrification inhibition. In the second study, a pairwise combinatorial approach was employed to assess the interactions among biochemically distinct metabolites co-exuded by Kernza® – caffeic acid, vanillic acid, vanillin, and phenylalanine – against multiple ammonia-oxidisers and soil nitrification. It was found that the metabolites interacted both synergistically and antagonistically against the test strains and soil nitrification, with antagonism being the most predominant interaction among the metabolites. Caffeic acid exhibited single agent dominance (SAD), dominating all other metabolites in all combinations. Furthermore, nitrifiers responded differentially to the metabolites – affirming that nitrifiers are differentially sensitive to inhibitors. Both individual and paired metabolites inhibited the growth of multiple AOB and AOA, as well as soil nitrification – suggesting that both synergism and antagonism did not impair the inhibitory potentials of the metabolites. This evidence suggests that biochemically distinct metabolites exuded by Kernza® and other BNI-positive plants may be interacting in diverse ways in the rhizosphere to suppress nitrification. The third study assessed the impact of Kernza®-induced perennialization on rhizomicrobiome and root endophytes in comparison to annual wheat under an agroclimatic gradient (Sweden, France, and Belgium). The results suggest pronounced similarities in the rhizobacterial composition of Kernza® and annual wheat, with no significant difference in the alpha diversity of their rhizomicrobiome. Beta diversity analysis revealed that factors such as country (agroclimatic conditions), sampling depth (spatial), and year (temporal) rather exerted greater influence than crop type. Notwithstanding, Kernza® promoted the stability of the rhizomicrobiome than annual wheat based on year-on-year comparison – suggesting that perennialization has the ability to protect rhizomicrobiome from ecological perturbation. Moreover, Kernza® recruited and internalised a higher proportion of the rhizosphere microbiome into its root tissues compared to annual wheat, indicating a potential role of crop-associated microbiomes in the lifecycle of Kernza®. Furthermore, an environment-wide comparison with agroecologically relevant database revealed that Kernza®, compared to annual wheat, harboured a significant proportion of rhizobacterial taxa associated with the rhizosphere and grassland ecosystems – supporting the notion that Kernza® shares ecological characteristics with natural grasslands. This study adds to the growing body of knowledge on the rhizosphere ecology of Kernza® and provides further evidence for the ecosystem service potential of Kernza®.