M. Cristina Romero

Cadmium removal capacities of filamentous soil fungi isolated from industrially polluted sediments, in La Plata (Argentina)

Aspergillus terreus, Cladosporium cladosporioides, Fusariumoxysporum, Gliocladium roseum, Penicillium spp., Talaromyces helicus and Trichodermakoningii were isolated from heavily polluted streams near an industrial area in La Plata, Argentina. The fungi were obtained from sediments with 0.25–0.50 mg Cd/l and they were isolated in cadmium-basal medium. They were then cultivated to evaluate their Cd detoxification abilities. The biomass developed in static assays represented 5–53% of the yield of stirred cultures, for the different fungal species, although the cadmium absorption were similar in both cases. These soil fungi represented 50% of the total isolates and their mycelial growth was conspicuous in these polluted sediments. Although bacteria have been mentioned as active microorganisms against heavy metals, the mycelial fungi were able to develop a significantly higher mass to sequestrate more metals. Thus, they could be used in remediation biotechnology to improve the Cd detoxification of chronically contaminated habitats.

Pyrene degradation by yeasts and filamentous fungi

The saprotrophic soil fungi Fusarium solani (Mart.) Sacc., Cylindrocarpon didymum (Hartig) Wollenw, Penicillium variabile Sopp. and the yeasts Rhodotorula glutinis (Fresenius) Harrison and Rhodotorula minuta (Saito) Harrison were cultured in mineral medium with pyrene. The remaining pyrene concentrations were periodically determined during 20 incubation days, using HPLC. To assess the metabolism of pyrene degradation we added 0.1 microCi of [4,5,9,10] 14C-pyrene to each fungi culture and measured the radioactivity in the volatile organic substances, extractable, aqueous phase, biomass and 14CO2 fractions. The assays demonstrated that F. solani and R. glutinis metabolized pyrene as a sole source of carbon. Differences in their activities at the beginning of the cultures disappeared by the end of the experiment, when 32 and 37% of the original pyrene concentration was detected, for the soil fungi and yeasts, respectively. Among the filamentous fungi, F. solani was highly active and oxidized pyrene; moreover, small but significant degradation rates were observed in C. didymum and P. variahile cultures. An increase in the 14CO2 evolution was observed at the 17th day with cosubstrate. R. glutinis and R. minuta cultures showed similar ability to biotransform pyrene, and that 35% of the initial concentration was consumed at the end of the assay. The same results were obtained in the experiments with or without glucose as cosubstrate.

Selection of autochthonous yeast strains able to degrade biphenyl

In order to assess the role of yeasts in the natural detoxification process of sediments polluted with biaryl compounds, indigenous yeast species able to degrade biphenyl (BP) were isolated and identified. The degradation ability of 24 strains of the genera Candida spp., Cryptococcus spp., Pichia spp., Rhodotorula spp., Trichosporon spp. and Yarrowia spp. was evaluated by the identification of the BP-metabolites, by HPLC analysis. 4-Hydroxybiphenyl was the main derivative in the Candida krusei, C. tenuis, C. tropicalis, Pichia haplophila, Rhodotorula glutinis, Trichosporon pullulans and Yarrowia lipolytica cultures. 3-Hydroxybiphenyl was detected in minor amounts in the culture supernatant of C. tropicalis, C. krusei strains and R. glutinis. Further hydroxylation led to 3,4-dihydroxy and 2,3-dihydroxybiphenyl; the former in C. tropicalis, C. krusei and R. glutinis cultures, and the latter only in the R. glutinis assays. The cleavage product 4-phenyl-2-pyrone-6-carboxylic acid, was observed in R. glutinis and Y. lipolytica cultures. The degradation ability of the R. glutinis isolates was noteworthy; as four hydrolxylated intermediates and a ring-cleavage product were obtained in both strain cultures. The species studied in this report were dominant in polluted sediments; furthermore, R. glutinis had been mentioned as able to degrade other aromatic hydrocarbons and had high relevance in bioremediation experiments.

Effects of heavy metals on microbial activity of water and sediment communities

The effects of Cd2+, Cr3+ and Zn2+ on the microbial activity of water and sediment samples from a contaminated stream were studied. The maximum [14C]glucose uptake (Vmax) and the mineralization (14CO2) rates were determined. A 10% reduction in Vmax was obtained at lower metal concentrations in water samples than in sediment ones. Moreover, a 10% decrease in 14CO2 was observed at significantly minor metal levels, so 14CO2 was more sensitive to evaluated heavy metal pollution. On the basis of MICs obtained for both communities, they were more sensitive to Cd2+ than to Cr3+ and Zn2+. Zinc was less inhibitory to Vmax and 14CO2 rates; Cr3+ showed an intermediate toxicity, and Cd2+ was 10–100 times more inhibitory than the other metals.

Biosorption of heavy metals by Talaromyces helicus: a trained fungus for copper and biphenyl detoxification

At present, it is common to observe environments with organic and inorganic pollution, defined as co-contamination. Most industrial and urban effluents releases both pollutant types, leading to a complex environmental problem, as the biota must be tolerant to both xenobiotics. T. helicus , an efficient strain to degrade biphenyl, was trained with high copper levels, and became co tolerant to cobalt, lead and cadmium when was cultured in their presence. The copper adaptation was the result of physiological mechanisms, and the activated biochemical processes conferred resistance to Cu 2+ as well as to other heavy metals. Furthermore, the Cu 2+ adaptation of the mycelium was also transferred to the spores, that removed twice as much copper from solution than those of the no trained parentals. Interestingly, metals combinations were less toxic than single ones, and co tolerance development indicated that the cellular mechanisms that conferred resistance were non-specific, so the micobiota isolated from co contaminated environments often exhibited resistance to more than one ions. These results emphasized the detoxification abilities of T. helicus and the adaptation to heavy metals and biarylic compounds. This data is significant for the environmental biotechnology, suggesting that such tolerance and co tolerance could be acquired in natural environments. So a simple bioremediation strategy could enhance the detoxification of these polluted areas, as the degrader organisms could be present.

Physiological and morphological characteristics of yeasts isolated from waste oil effluents

Pichia membranaefaciens, Cryptococcus laurentii, Rhodotorula glutinis and Candida krusei were isolated from contaminated sites. A significant variability in cell forms and in assimilation profiles was observed in the C. krusei strains. The chitin synthase activity and chitin content allowed us to differentiate three strain types. The variability of the phenotypic traits was higher in C. krusei strains isolated from heavily polluted sites.

Sorbed Anthracene Degradation by Sophorolipid Producing Yeasts

The organic pollutan adsorption/desorption process by microbial degradation had been less studied than metal ones. The sorption assays alone did not predict desorption, due to hysteresis, irreversibility, fixed compounds in different sites, with diverse desorption rates. Most of the studies dealt with bacteria rather than filamentous fungi and yeasts. So, our aims were to isolate yeasts from polluted sediments, to quantify its potential to uptake anthracene (An) and to evaluate the bioavailability by a desorption model. Yeasts were isolated from hydrocarbon-polluted samples, 40-isolates grew in anthracene-plates. Molecular characterization was achieved by sequence analysis of the ITS1-5.8S rRNA-ITS4 and 26S rRNA regions; morphological and physiological determination were also done. Candida parasilopsis , Pichia anomala and Rhodothorula mucilaginosa were the prevalent yeasts. An-degradation was assessed in soil-systems with 0, 50, 100, 150, 200 and 250 I¼g An/l, 3 differentes sorbens types, organic carbon, organic nitrogen, PAHs, sand:silt:clay, pH and cation exchange capacity. Sophorolipids excretion were confirmed by HPLC, UV-detector with active fraction at 9.669 min (RT 9.646 min = sophorolipid-standard). A desorption model with equilibrium, nonequilibrium and nondesorption areas, was applied to explain the experimental data, An-transformation was greater in the organic liquid-phase than in the soil-sorbed ones; the desorption-coefficients and soil components were negatively correlated with the kinetic parameters. The An-release depended on the sophorolipid excretion, soil matrix and particles sizes. Desorption parameters significantly fitted the yeast uptake, with R 2 = 0.97, R 2 = 0.90 and R 2 = 0.97 for C. parasilopsis , P. anomala and R. mucilaginosa, respectively.