Biodegradation capability of Absidia fusca Linnemann towards environmental pollutants

Response of Poplar and Associated Fungal Endophytic Communities to a PAH Contamination Gradient

Microbial populations associated to poplar are well described in non-contaminated and metal-contaminated environments but more poorly in the context of polycyclic aromatic hydrocarbon (PAH) contamination. This study aimed to understand how a gradient of phenanthrene (PHE) contamination affects poplar growth and the fungal microbiome in both soil and plant endosphere (roots, stems and leaves). Plant growth and fitness parameters indicated that the growth of Populus canadensis was impaired when PHE concentration increased above 400 mg kg^-1. Values of alpha-diversity indicators of fungal diversity and richness were not affected by the PHE gradient. The PHE contamination had a stronger impact on the fungal community composition in the soil and root compartments compared to that of the aboveground organs. Most of the indicator species whose relative abundance was correlated with PHE contamination decreased along the gradient indicating a toxic effect of PHE on these fungal OTUs (Operational Taxonomic Units). However, the relative abundance of some OTUs such as Cadophora, Alternaria and Aspergillus, potentially linked to PHE degradation or being plant-beneficial taxa, increased along the gradient. Finally, this study allowed a deeper understanding of the dual response of plant and fungal communities in the case of a soil PAH contamination gradient leading to new perspectives on fungal assisted phytoremediation.

Degradation pathway of pentachlorophenol by Mucor plumbeus involves phase II conjugation and oxidation-reduction reactions

Environmental pollution by pentachlorophenol (PCP) is a critical concern worldwide and fungal bioremediation constitutes an elegant and environment-friendly solution. Mucorales from the Zygomycota phylum are often observed to be competitive in field conditions and Mucor plumbeus, in particular, can efficiently deplete PCP from media. The pathway for PCP degradation used by this fungus has not been investigated. In this study, PCP-derived metabolites were identified by liquid chromatography coupled with quadrupole time-of-flight mass spectrometry, including tetra- and tri-chlorohydroquinones and phase II-conjugated metabolites. Amongst the latter are the previously reported glucose, sulfate and ribose conjugates, and identified for the first time in fungi sulfate-glucose conjugates. A PCP transformation pathway for M. plumbeus is proposed, which excludes the involvement of cytochrome P-450 and extracellular ligninolytic enzymes.

Photolysis of the herbicide sulcotrione: formation of a major photoproduct and its toxicity evaluation

BACKGROUND

Sulcotrione is a selective herbicide marketed for use in maize since 1993, but its environmental fate is not yet fully elucidated. A major metabolite resulting from cleavage between the two ring moieties, leading to 2-chloro-4-mesylbenzoic acid (CMBA), has been identified; it presents a rather low toxicity. In photochemical studies this compound has also been claimed to be formed in high proportions. The present authors recently found that, under irradiation, sulcotrione mainly yields a cyclization product (CP). Thus, Sulcotrione photochemistry is still a matter of debate. The aim of the present work was to give an unequivocal answer to this issue. The potential toxicity of CP, CMBA and sulcotrione towards three organisms considered as representative of aquatic ecosystems was also evaluated.

RESULTS

The main transformation product of sulcotrione is the cyclization product (CP), and CMBA is formed in smaller amounts. For the toxicological approach, the tested organisms were a bacterium, Vibrio fischeri (Bejerinck) Lehmann & Neumann, an alga, Pseudokirchneriella subcapitata (Korshikov) Hindak, and a protozoan, Tetrahymena pyriformis (Ehrenberg) Lwoff. Sulcotrione is more harmful towards the alga, but CP is more toxic to the bacterium and the protozoan. It must be noted that the measured toxicities are nonetheless rather low.

CONCLUSION

On irradiation, sulcotrione mainly gives the photocyclization product, which presents a higher toxicity than sulcotrione and CMBA. This cyclization product should thus be considered in sulcotrione environmental risk assessment.

Involvement of Tetrahymena pyriformis and selected fungi in the elimination of anthracene, and toxicity assessment of the biotransformation products

Anthracene (AC) is a non-mutagenic and non-carcinogenic, low-molecular-weight polycyclic aromatic hydrocarbon present in the environment. Its toxicity can be dramatically increased after solar-light exposure. Biotransformation capacities of AC by Tetrahymena pyriformis and a selection of eight micromycetes were studied, and the ability of these microorganisms to detoxify the polluted ecosystems was assessed. We showed that T. pyriformis was able to accumulate high amounts of AC without any transformation. In contrast, the fungi Cunninghamella elegans, Absidia fusca, Absidia cylindrospora, Rhodotorula glutinis, and Aspergillus terreus were able to transform AC with a high efficiency. Cytotoxicity assays conducted on HeLa cells and T. pyriformis showed that crude extract from A. fusca culture medium obtained after AC biotransformation was not toxic. For A. fusca and A. cylindrospora, 1-4 dihydroxyanthraquinone was shown to be the major product during the biotransformation process. This compound seemed to be a dead-end metabolite at least for the Absidia strains. The cytotoxicity of 1-4 dihydroxyanthraquinone was higher than that of AC to T. pyriformis but lower to HeLa cells. On the whole our results showed that the microorganisms studied were all able to decontaminate an AC-polluted ecosystem, either by accumulating or transforming the compound. A possible detoxification process resulting from AC biotransformation can be considered only using the human cell model.

Pentachlorophenol inhibits micronuclei induction by 2-acetylaminofluorene but not by thioacetamide

Our study examined the capacity of pentachlorophenol (PCP) to inhibit the ability of 2-acetylaminofluorene (2-AAF) and thioacetamide (TAA) to induce micronuclei in mouse bone marrow cells in vivo. 2-AAF (5.6mg/kg) and TAA (60mg/kg) were administered intra-peritoneally (i.p.) to Mus musculus males (BALB/c), and the frequencies of polychromatic erythrocytes with micronuclei (PCE-MN) 24h after injection were analyzed. Treatment with 2-AAF or TAA resulted in high PCE-MN frequencies in comparison with untreated and negative controls (19.9 and 21.6‰, respectively, versus ≈3‰). Pretreatment with a single PCP dose (44mg/kg) 24h prior to the 2-AAF administration virtually eliminated micronuclei formation by 2-AAF, although it had no inhibitory effect on TAA-induced micronuclei. Animals receiving cyclophosphamide (CP) served as positive control. Since PCP is known to inhibit arylsulfotransferase (AST) activity, which is involved in 2-AAF activation, this mechanism most likely produced the results with PCP and 2-AAF. Our results also are consistent with a different pathway involved in TAA induction of micronuclei, one that is not inhibited by PCP.

Assessment of anthracene toxicity toward environmental eukaryotic microorganisms: Tetrahymena pyriformis and selected micromycetes

The toxicity of anthracene, a nonmutagenic, noncarcinogenic, low-molecular-weight polycyclic aromatic hydrocarbon present in the environment, was assessed using a ciliated protozoan, Tetrahymena pyriformis, and a selection of 10 micromycetes from different taxonomic groups living in two environmental compartments, namely aquatic and soil ecosystems. With T. pyriformis, a concentration-dependent inhibitory effect was shown on the cell proliferation rate, IC(50) = 33.40+/-4.84 mg/L (kinetic method). Phagocytosis of nonsoluble anthracene was confirmed by the presence of digestive vacuoles with photon microscopy. In fungi, anthracene did not exhibit a fungicide effect but showed a fungistatic action. Except for Absidia fusca and Cladosporium herbarum, the micromycetes showed a concentration-dependent decrease in growth. From IC(50) values determined by endpoint or kinetic methods, Rhodotorula glutinis and all of the Ascomycotina (except for Penicillium chrysogenum) were the most sensitive species, while Phanerochaete chrysosporium, P. chrysogenum, and the two Deuteromycotina were more resistant to anthracene. Our discussion focuses on the evaluation of toxicity by the two methods used for the calculation of the IC(50) values (endpoint and kinetic), the advantages of studying growth by a kinetic method (the dynamic aspect), and a comparison of toxicity to T. pyriformis and the different micromycetes.

Degradation of phenol and cresols at low temperatures using a suspended-carrier biofilm process

Degradation of phenol and o-, m- and p-cresol at a concentration of 150 mg l(-1) of each compound was studied in a suspended-carrier biofilm process consisting of two aerobic stages. The fungus Mortierella sarnyensis Mil'ko dominated the microflora in the first reactor, while bacteria dominated in the second reactor. The process was studied at 4, 7, 11 and 15 degrees C. The results from the experiments showed the process to be relatively efficient even at 4 degrees C. The degradation rate was 33% of that at 15 degrees C for o-cresol. Both phenol and the cresols were degraded in the first reactor and a new peak appeared in the HPLC-chromatograms indicating the formation of one or more intermediate compounds in the first stage. These compounds were however degraded to below the detection limit in the second reactor. Small new peaks appeared in the chromatograms of the outlet from the second reactor at the maximum loading rates.