Chemical and biological recovery of soils contaminated with antimony using eco-friendly materials

Antimony (Sb), a non-essential plant element, can be present in soils and waters in very high concentrations often due to a variety of anthropogenic activities. Though antimony is classified as a pollutant of priority interest, very little is known about its environmental behaviour and soil speciation. In recent years, different sorbents for the in-situ remediation of metalloid-polluted soils were proposed and tested with variable success. In a search for alternative, low-cost and environmental friendly Sb sorbents, drinking water treatment residuals (WTRs), the waste material resulting from the treatment of surface or ground water, and municipal solid waste compost (MSWC) were identified as potential good candidates. In this PhD thesis we showed that the Sb mobility, and its impact on the microbial and biochemical features of two soils artificially contaminated, were highly influenced by selected soil properties such as pH and organic matter content. Both WTRs and MSWC were able to act as effective Sb(V)-immobilizing agents in aqueous solutions especially at acidic pH (i.e. 4.5). Moreover, when added to a contaminated mine soil, the combination of both sorbents significantly reduced the mobility of antimony, alleviated its impact on soil microbiota and promoted a recovery of soil biochemical functioning. Plant growth (Helichrysum italicum L.) in the amended soil was finally enhanced while the Sb uptake was definitively reduced

Novel bioactive metabolites from new or rare fimicolous fungi to be used against plant pathogenic fungi

Herbivores mammals dung allows the growth of a wide variety of fimicolous fungi. New molecular techniques together with the more classical morphological approach make possible the identification of new species of fimicolous fungi, whose number is steadily increasing. In order to grow on a complex ecosystem, such as herbivores dung, fimicolous fungi produce a wide variety of secondary metabolites, helping them to compete with other organisms. However, bioactive metabolites produced by fimicolous fungi, especially those with antifungal activity, have been mainly evaluated for a possible application in medical field but no information are available concerning a possible use against plant pathogenic fungi. The aim of this thesis is to investigate the possible use of these secondary metabolites in the agricultural sector, mainly against plant pathogenic fungi within a sustainable crop protection strategy. The present work has been performed on three quite recently described fimicolous isolates: Cleistothelebolus nipigonensis (DSM 26817), Neogymnomyces virgineus (MB561628), Rodentomyces reticulatus (MB516520) and on two new strains of Auxarthron spp. (10405 and 10406), these last isolated, identified and described within this work. All isolates used in this work derived from herbivorous dung. Auxarthron spp. 10405 and 10406 have been firstly identificated by morphological and molecular analysis and then assigned to Auxarthron umbrinum and Auxarthron concentricum species, respectively. Further, these two isolates have been submitted to cultural studies on different substrates and at different temperatures, resulting unable to grow at 37°C, then excluding a possible pathogenicity for humans. Finally, these two isolates, together with the other listed before, were evaluated for their antifungal activity against some important plant pathogenic fungi, showing encouraging results. In order to obtain diffusible secondary metabolites to be evaluated for their antifungal activity, a fermentation protocol of the five fungal isolates have been setted-up. Different substrates were evaluated, in order to select one which allowed to maximize the development of the fungal biomass. Solid State Fermentation (SSF) allowed an higher biomass production, than Liquid State Fermentation and rye flour was selected as substrate. The extraction and the purification - led by essays of antibiosis activity conducted in parallel - of metabolites from SSF substrate were carried out by Prof. Antonio Evidente from the Department of Chemical Sciences (University Federico II of Naples). From the first extraction, we obtained an aqueous phase and two organic phases (n-hexane and dichloromethane). Only organic extracts obtained from C. nipigonensis and N. virgineus showed strong antifungal activity against Alternaria brassicicola, Fusarium graminearum and Botrytis cinerea. The subsequent purification of the organic extracts resulted in the isolation of fractions and of two pure metabolites: Fusaproliferin and Terpestacin. These pure metabolites and their derivates (various compounds acetylated and methylated) were further tested against plant pathogenic fungi in order to confirm their activity. Finally, all metabolites showing antifungal activity were further used in a phytotoxicity test on tomato and cabbage plants, resulting not phytotoxic. Fimicolous fungi can be, then, considered a rich source of antifungal metabolites to be exploited both in medicine and in agriculture, this last replying to the increasing demand of an ecofriendly approach in crop protection

A polyphasic contribution to the knowledge of Auxarthron (Onygenaceae)

In a survey of coprophilous fungi in Italy, two intersting ascomycetes were recovered from hedgehog dung. These fungi showed a sexual morph characterized by gymnothecia, globose reticulate ascospores, a Malbranchea asexual state and a keratinolytic ability, and were identified morphologically and molecularly as Auxarthron umbrinum and A. concentricum of the Onygenaceae. The history, ecology, and morphology of the genus Auxarthron as a whole, and of A.umbrinum and A. concentricum in particular, are extensively covered. A preliminary evaluation of the antagonistic properties of Auxarthron umbrinum and A. concentricum against fungi of a phytopathogenic interest has been performed in dual cultures. Growth inhibition of some plant pathogenic fungi was recorded, and the effects were growth medium dependent. When Solid State Fermentation (SSF) substrate of both Auxarthron isolates has been submitted to extraction, both the organic extract residues (n-hexane and CH2Cl2) and the lyophilized aqueous phases were used for the antibiotic test against plant pathogenic fungi. Significant antifungal activity was obtained by organic fractions and aqueous residue of A. concentricum against A. brassicicola and B. cinerea whereas A. umbrinum appeared to be less effective. Finally, analysis of ITS nrDNA sequences suggests that an extensive phylogenetic revision of the genus Auxarthron is necessary

Fusaproliferin, Terpestacin and Their Derivatives Display Variable Allelopathic Activity Against Some Ascomycetous Fungi

Herbivorous mammal dung supports a large variety of fimicolous fungi able to produce different bioactive secondary metabolites to compete with other organisms. Recently, the organic extracts of the Solid State Fermentation (SSF) cultures of Cleistothelebolus nipigonensis and Neogymnomyces virgineus, showing strong antifungal activity, were preliminarily investigated. This manuscript reports the isolation of the main metabolites identified, using spectroscopic and optical methods, as fusaproliferin (1) and terpestacin (2). Furthermore, some key hemisynthetic derivatives were prepared and their antifungal activity was tested against the same fungi previously reported to be affected by the organic extracts obtained from SSF. These metabolites and their derivatives resulted able to reduce the growth of Alternaria brassicicola, Botrytis cinerea and Fusarium graminearum in a variable extent strongly dependent from chemical modifications and test fungi. The hydroxy enolic group at C(17) appeared to be a structural feature important to impart activity. This study represents the first report of these secondary metabolites produced by C. nipigonensis and N. virgineus

Insights into the fate of antimony (Sb) in contaminated soils: ageing influence on Sb mobility, bioavailability, bioaccessibility and speciation

The effect of long-term ageing (up to 700 days) on the mobility, potential bioavailability and bioaccessibility of antimony (Sb) was investigated in two soils (S1: pH 8.2; S2: pH 4.9) spiked with two Sb concentrations (100 and 1000 mg.kg(-1)). The Sbmobility decreased with ageing as highlighted by sequential extraction, while its residual fraction significantly increased. The concentration of Sb (CDGT), as determined by diffusive gradients in thin films (DGT), showed a reduction in potential contaminant bioavailability during ageing. The DGT analysis also showed that Sb-CDGT after 700 days ageing was significantly higher in S1-1000 compared to S2-1000, suggesting soil pH plays a key role in Sb potential bioavailability. In-vitro tests also revealed that Sb bioaccessibility (andHazard Quotient) decreased over time. Linear combination fitting of Sb K-edge XANES derivative spectra showed, as a general trend, an increase in Sb(V) sorption to inorganic oxides with ageing as well as Sb(V) bound to organic matter (e.g. up to 27 and 37% respectively for S2-100). The results indicated that ageing can alleviate Sb ecotoxicity in soil and that the effectiveness of such processes can be increased at acidic pH. However, substantial risks due to Sb mobility, potential bioavailability and bioaccessibility remained in contaminated soils even after 700 days ageing. (C) 2021 Elsevier B.V. All rights reserved

Bioactive metabolites from new or rare fimicolous fungi with antifungal activity against plant pathogenic fungi

Herbivorous mammals dung support a large variety of fimicolous fungi and the number of new genera and species is constantly increasing. Dung is a complex ecosystem and to win the struggle for life, these fungi produce a plethora of bioactive secondary metabolites to compete with other organisms. Fimicolous fungi and their bioactive metabolites are mostly evaluated for a possible use in medicine. Very few information are available about their possible exploitation in agriculture against plant pathogens. One isolate of each of the fimicolous fungi Cleistothelebolus nipigonensis, Neogymnomyces virgineus and Rodentomyces reticulatus, collected from dung of different herbivorous, were investigated. Only the organic extracts of Solid State Fermentation (SSF) cultures of C. nipigonensis and N. virgineus grown on rye flour showed strong antifungal activity against fungal pathogens of some important crops. The purification of the organic extracts allowed to obtain different fractions and the isolation of some pure metabolites and their preliminary chemical and biological characterization are reported in this manuscript

Long-term effect of municipal solid waste compost on the recovery of a potentially toxic element (PTE)-contaminated soil: PTE mobility, distribution and bioaccessibility

Compost from municipal solid waste (MSWC) can represent a resource for the environmental management of soils contaminated with potentially toxic elements (PTEs), since it can reduce their mobility and improve soil fertility. However, the long-term impact of compost on soil recovery has been poorly investigated. To this end, the influence of a MSWC added at different rates (i.e. 1.5, 3.0 and 4.5% w/w) to a multi-PTE-contaminated (e.g. Sb 412 mg kg-1, Pb 2664 mg kg-1 and Zn 7510 mg kg-1) sub-acidic soil (pH 6.4) was evaluated after 6 years since its addition. The MSWC significantly enhanced soil fertility parameters (i.e. total organic carbon, Olsen P and total N) and reduced the PTE labile fractions. The distribution maps of PTEs detected through μXRF analysis revealed the presence of Zn and Pb carbonates in the amended soils, or the formation of complexes between these PTEs and the functional groups of MSWC. A higher oral, inhalation and dermal bioaccessibility of each PTE was detected in the soil fine-grained fractions (< 2 and 2-10 μm) than in coarse particles (10-20 and 20-50 μm). The MSWC amendment generally did not modify the PTE bioaccessibility, while the relative bioaccessibility of cationic PTEs was greater than that of anionic ones (e.g. Cd > Zn > Pb > Sb > As). Pb and Sb showed the highest hazard quotients (e.g. 2.2 and 10 for Sb and Pb, respectively, in children). Overall, the results indicated that the MSWC used can be an effective option for the recovery of PTE-contaminated soils, even in the long term