Study of the bioremediatory capacity of wild yeasts

Microbial detoxification has been proposed as a new alternative for removing toxins and pollutants. In this study, the biodetoxification activities of yeasts against aflatoxin B1 and zinc were evaluated by HPLC and voltammetric techniques. The strains with the best activity were also subjected to complementary assays, namely biocontrol capability and heavy-metal resistance. The results indicate that the detoxification capability is toxin- and strain-dependent and is not directly related to cell growth. Therefore, we can assume that there are some other mechanisms involved in the process, which must be studied in the future. Only 33 of the 213 strains studied were capable of removing over 50% of aflatoxin B1, Rhodotrorula mucilaginosa being the best-performing species detected. As for zinc, there were 39 strains that eliminated over 50% of the heavy metal, with Diutina rugosa showing the best results. Complementary experiments were carried out on the strains with the best detoxification activity. Biocontrol tests against mycotoxigenic moulds showed that almost 50% of strains had an inhibitory effect on growth. Additionally, 53% of the strains grew in the presence of 100 mg/L of zinc. It has been proven that yeasts can be useful tools for biodetoxification, although further experiments must be carried out in order to ascertain the mechanisms involved.

www.nature.com/scientificreports/ is especially problematic in tropical and subtropical areas, although the Mediterranean area has become prone to aflatoxin contamination due to a shift in traditional occurrence areas caused by climate change 12 . Mycotoxins can be controlled not only directly on the substrate but also through biological control against mycotoxigenic moulds.
In the latter case, biological material, such as microorganisms, is used to inhibit the growth of organisms 13 . Numerous strategies have been developed for solving the environmental and security problems posed by the toxic components outlined above. The main advantage of using yeasts in biodetoxification techniques is that most of the species are safe for living organisms. These yeasts grow on a wide range of substrates and have an ample metabolic diversity.
Studies carried out on the biodetoxification capability of yeast have revealed that some Saccharomyces and non-Saccharomyces strains are easily able to eliminate heavy metals found in wastewater from the food industry [14][15][16] . It is also known that yeast cell walls are capable of adsorbing certain mycotoxins during fermentation processes and in final food products 14,[17][18][19] .
Given the background provided above, the purpose of this article is to establish a protocol that would allow an assessment of the detoxification capability of yeast strains isolated from natural ecosystems and to use this approach for selecting the most promising yeasts. Zn, which is especially present in urban wastewaters and has an impact on both aquatic environments and human health, and AFB 1 , a dangerous toxin often leading to food loss and food safety problems worldwide, were selected for this study and their elimination by this technique will be examined.

Materials and methods
Yeast strains. A total of 213 yeast strains isolated from different elements, such as flowers, animals, water, and soil, and also from the food industry environment, were studied [unpublished data]. All the isolates were identified at species and strain level in a previous study (Table 1), with a total of 20 different species. The majority of the isolates were from the genera Diutina, Saccharomyces, Candida, and Rhodotorula. All yeasts were grown in YPD broth (yeast extract 10 g/L; glucose 20 g/L; peptone 20 g/L), incubated at 30 °C for 24 h, and gently stirred to obtain young cultures. Chemicals and media. AFB 1 (≥ 98.0% purity) and zinc nitrate (99.0% purity) were purchased from Sigma-Aldrich (U.S.) and Merck (Germany), respectively.
A minimal salts medium (MSM) containing K 2 HPO 4 0.4 g, KH 2 PO 4 0.2 g, NaCl 0.1 g, MgSO 4 .7H 2 O 0.5 g, MnCl 2 0.01 g, Fe(SO 4 ) 3 0.01 g, and Na 2 MoO 4 0.01 g per litre was used for the detoxification assay and the pH was adjusted to 7 as proposed by Abigail and Das 20 . The sterilized medium was supplied with AFB 1 from a 400 mg/L stock solution in methanol (99.9% purity) or with Zn (Zn(NO 3 ) 2 ) from a 100 mg/L stock solution in demineralized water. All solutions were pasteurised (75 °C/5 min) or filtered through a cellulose acetate membrane (0.22 µm/diameter) before being added to the MSM. The final concentrations were 0.04 mg/L for AFB 1 MSM and 1 mg/L for Zn MSM. www.nature.com/scientificreports/ Setting up the detoxification method. Saccharomyces cerevisiae (EB62 and EB83) and Pichia krudiavzevii (AK8) were the three representative strains chosen in order to identify the best conditions for a reliable and reproducible detoxification protocol. The following parameters were studied: Temperature and contact time. The three strains were inoculated in 25 mL of the defined medium (MSM + toxin) at different temperatures (25 and 30 °C) and for different times (3 and 5 days). The temperature conditions were assayed by establishing a standard time of 5 days for each experiment. The results obtained in this step allowed the temperature to be adjusted and an assessment of the effect of time on cell viability to be made. In total, 12 yeast counts, including duplicates, were carried out for each MSM plus toxin assay.
Standardisation of the method used for toxin analysis. Zinc. Voltammetric measurements were performed with a Metrohm Computrace voltammetric analyser potentiostat (model 757 VA, Eco-Chemie, Utrecht, The Netherlands). A conventional three-electrode system-consisting of an Ag/AgCl/KCl reference electrode, a hanging mercury drop electrode (HMDE) as the working electrode, and a platinum rod as the auxiliary electrode-was used. All measurements were automated and controlled through the programming capacity of the apparatus. The data were treated with a Computrace 757 VA electrochemical analyser. In order to ascertain whether the yeasts interacted with the electrode, thus causing a lack of sensitivity in the measurements, a comparison between the medium with and without cells was carried out in duplicate. One S. cerevisiae strain was grown in MSM + Zn, and the supernatant was obtained by centrifugation (4,500 rpm, 4 min, 10 °C) or filtration through 0.2 µm cellulose acetate membrane (VWR Int., U.S.) for quantification of Zn. These samples were analysed along with those with cells and the results were compared.
To determine whether pH influenced the results, both the direct supernatant (pH 7) and a sample adjusted to normal Zn analysis conditions (pH 2) were measured, with a variation in the ionic forces ranging from 10 to 50 mM. Moreover, different accumulation times (0, 15, and 30 s) and accumulation potentials (from − 1.1 to − 1.5 V) were checked for MSM + Zn, with and without grown strains, to observe where the most sensitive voltammetric signal was obtained. For the adjustment, the tested sample was compared with a standard solution as positive control (1 mg/L Zn solution).
Aflatoxin B 1 . For AFB 1 , a 1,260 Infinity HPLC system, coupled to a 6,545 Quadrupole-Time-of-Flight (QToF) spectrometer, was used for the analysis, in conjunction with a mass detector (Agilent, Waldbronn, Germany) and control software (Mass Hunter Workstation; version B.06.11). The analysis parameters and conditions were as described by Iriondo-DeHond et al. 21 . In brief, samples were injected into a Zorbax Eclipse Plus C18 Rapid Resolution HD Column (2.1 × 50 mm, 1.8 μm, Agilent, Santa Clara, CA) with a 5 mm guard column. The temperature was set at 30 °C and the mobile phase was 5 mM ammonium formate + 0.1% formic acid and 5 mM ammonium formate + 0.1% formic acid in methanol. The gradient elution was chosen as indicated in the procedure. Finally, compounds were identified and quantified using the 'Find by Formula' algorithm.
Samples were directly centrifuged according to the protocol described by Joannis-Cassan et al. 22 . Different methodologies were proposed for the extraction of AFB 1 : extraction with organic solvents (ethyl acetate or methanol) or the use of a solid phase extraction column (ISOLUTE Myco, Biotage, Sweden). Quantification was achieved by injecting standard solutions from 0.005 to 0.04 mg/L at different sample volumes (10 µL and 30 µL).
Detoxification assay: determination of residual toxin concentration and cell viability. Residual toxin concentration. The best conditions described in the previous section were employed and all yeasts (213) were assayed to ascertain their potential binding capability. Batch experiments were carried out in 100 mL Erlenmeyer flasks containing 25 mL of MSM with each toxin (1 mg/L of Zn and 0.04 mg/L AFB 1 ) and then inoculated with 10 6 cells/mL from overnight cultures. Cell density was measured by microscope count using a Thoma chamber. The samples in the Erlenmeyer flasks were incubated with gentle stirring (150 rpm). Duplicate aliquots were taken at the beginning and at the end of the incubation period for toxin analysis. Two negative controls were also established: MSM without toxin supplied with cell suspension from each strain (NCY) and MSM with each toxin without yeast cells (NCT).
The toxin elimination capability of yeast was calculated using the following formula: C NCT refers to 'toxin concentration from NCT' and C S to 'toxin concentration from sample' .

Cell viability.
To determine whether the presence of toxins affected cellular viability as well as elucidate the possible mechanism of action (adsorption or metabolism), plate counts were carried out on YPD agar (yeast extract 10 g/L, glucose 20 g/L, peptone 20 g/L, agar 20 g/L) using a spiral plater (Eddy Jet 2, IUL Instruments, Barcelona, Spain). Plates were incubated at 30 °C for 2 days and colonies were counted with an automatic counter (Flash & Go, IUL Instruments, Barcelona, Spain). MSM without toxin was inoculated with the tested yeast and the sample was incubated for the same amount of time and at the same temperature to provide a negative control. www.nature.com/scientificreports/ were dropped (10 6 cells/mL) onto the same plate (three yeasts on each plate) and incubated at 30 °C for at least 5 days. Growth inhibition on the mould was observed by comparing the radium of the positive control (mould cultured alone on an agar plate) with the values for the samples with yeasts.
Tolerance to the presence of Zn in solid media. With the aim of selecting the strains with the best tolerance to Zn in the environment, cell suspensions of young cultures were centrifuged (4,500 rpm/5 min/25 °C) and the pellets were resuspended in YNB broth (Difco-BD, Madrid, Spain) and incubated for 6 h to deplete all sugar reserves. After this time, 10 6 cells/mL were dropped onto YM agar plates (yeast extract 3 g/L malt extract 3 g/L, peptone 5 g/L, glucose 10 g/L, agar 20 g/L) containing different Zn concentrations (1 mg/L, 25 mg/L, 50 mg/L, 75 mg/L, and 100 mg/L). Plates were incubated at 30 °C for 5 days and the adaptation capability with respect to Zn was observed by evaluating yeast growth.
Statistical analysis. Statistical

Results and discussion
Setting up the detoxification method. Temperature and contact time. Table 2 shows the best time and temperature conditions. The highest viabilities (log cells/ml) after 5 days were obtained at 30 °C for both MSM. Around 0.5 or 1 log unit was the difference between cells incubated at 25 °C and at 30 °C, as indicated by the Student's t-test (p < 0.005), and significant differences were observed between them in both media. When using 30 °C as the best temperature, counts were 0.5 log units higher at 5 days than at 3 days, with no significant differences (Student's t-test). Although the only significant differences were observed for temperature conditions, it was detected that incubation time had a less marked effect on the process than temperature. Therefore, the conditions selected were incubation at 30 °C for 5 days because, although counts at 3 days were similar, it appeared that more time was favourable for checking whether toxins were eliminated by secondary metabolism pathways 23,24 or were bioaccumulated 25 .
Standardisation of the method used for toxin analysis. Zinc. Yeasts incubated in MSM + Zn were treated at three different stages: (1) after a centrifugation step, (2) after a filtration step, or (3) with no treatment. The samples were then analysed by voltammetry with the mercury electrode (Table 3). It was evident that untreated aliquots presented lower sensitivity at the three accumulation times than centrifuged and filtered samples. This behaviour may have been due to the presence of cells interfering with the adequate accumulation and reduction of Zn ions at the mercury electrode. Similar values were obtained in the Zn voltammetry measurements on samples treated by the two methods mentioned above, with slightly higher values obtained for centrifuged samples when compared to filtered samples. Although both techniques showed the same sensitivity, centrifugation was selected as the cell removal treatment in order to standardise the method for both MSM supplied with toxins.
Regarding the adjustment of ionic strength in the potassium phosphate buffer used for the voltammetry measurements, different ionic buffer strengths were assessed (from 10 to 50 mM) at pH 7 in order to identify the Table 2. Conditions tested (temperature and time) in both contaminated medias (AFB1 and Zn) and counts (log) obtained (means ± SD). * and * 2 there are Significant differences between 2 group of samples obtained by Student's T-test.  These results indicate that an accumulation time of T0s showed a slight loss of sensitivity for Zn detection, while at T15s and T30s the measurements were very similar. The aforementioned loss was more acute for samples that contained higher Zn concentrations. All three tests showed optimal sensitivity, but, in order to save time, T15s accumulation was preferred, as it not only provides quick measurement but also does not present a loss of sensitivity. If necessary, in future studies, a second measurement at a higher accumulation time could be carried out for samples with lower Zn concentrations (e.g., 1 µg/L or 1 ng/L). The accumulation potentials for the Zn measurements were checked from -1.1 to -1.5 V and the calibration was based on the peak reduction signal, so a potential with less signal noise was chosen for the analysis. In this case, an accumulation potential of -1.2 V was selected. Based on the above results, the conditions selected for the quantification of residual Zn after the detoxification assay were as follows: centrifugation was chosen as the cell-removal technique, as it not only speeds up the process but also reduces the time and material consumed; 10 mM was selected as the ionic strength of the buffer; 15 s was selected as the accumulation time; and, finally, -1.2 V was employed as the accumulation potential.
Aflatoxin B1. From the three options tested for extraction, solid phase extraction columns constitute a good extraction method, but this method was impractical for a large number of samples, so it was ruled out for this experiment. Additionally, bibliographic research revealed that, although methanol is used for the extraction of other mycotoxins 17 , in aqueous samples ethyl acetate proved to have a higher extraction efficiency than methanol 26 . It is also a cheap low-toxicity solvent. Therefore, the same volume of supernatant and ethyl acetate (PanReac, Barcelona, Spain) were mixed for 1 min and the ethyl acetate phase was collected. AFB 1 suspensions were concentrated using a SpeedVac concentrator (Thermo Savant ISS110, New York, U.S.) and resuspended in a 20% Methanol/80% MilliQ water (v/v) solution. The six-point calibration curve allowed the high sensitivity and reproducibility of the method to be confirmed. All points were detected at both sample volume injections (10 µL and 30 µL), but 30 µL was selected as the injection volume based on previous studies on AFB 1

quantification 21 .
Detoxification assay: determination of residual toxin concentration and cell viability. Residual toxin concentration. The yeast strains (213) were inoculated in both MSM + Zn and MSM + AFB 1 to evaluate detoxification capability. The yeasts were grouped into three different sets according to toxin elimination percentage: (1) 0-25% elimination, (2) 25-50% elimination, and (3) over 50% elimination (Fig. 1). Detoxification behaviour was observed to be different between AFB 1 and Zn. Over 50% of the yeasts were able to eliminate AFB 1 . A large number of strains (102) detoxified AFB 1 by 25% to 50%, and 33 strains were able to remove over 50%. Regarding Zn, although 106 of the tested strains were not capable of eliminating more than 25%, 39 strains eliminated over 50% of the Zn. The 66 strains that eliminated over 50% of the toxins are listed in Table 5. Rh. mucilaginosa was the species with the most strains (22) with a high capability for AFB 1 elimination (around 65%), although it did not present the same efficiency against Zn, as only two strains were able to remove over 70% of the Zn.
Aureobasidium pullulans (H1) presented good behaviour with both toxins (almost 70% of AFB 1 and over 90% of Zn). Nevertheless, some species can eliminate over 90% of Zn but not AFB 1 , e.g., S. cerevisiae (EB21). The opposite behaviour was observed for EB16 (Rh. mucilaginosa), which was able to absorb 70% of the AFB 1 but eliminated less than 20% (data not shown). This would mean that the detoxification ability of strains is different depending on the toxin. Moreover, strain FP5 (D. rugosa) showed strong activity against Zn (nearly 100% removal), but it did not show any detoxification activity against the mycotoxin. The three K. pastoris (EW1, EW3, and EW6) strains exhibited good capability against the two toxins, with high percentages of elimination. Overall, strains from different species showed different behaviours against the two toxins, so this activity is clearly strain-dependent.
The use of yeast for mycotoxin detoxification has been reported previously by other authors 22,27 . It was shown that the percentage of mycotoxins adsorbed by yeast varied depending on the strain, with Rh. mucilaginosa strains removing higher percentages of other mycotoxins. In contrast, heavy metal detoxification by yeast has rarely been reported and most studies have been carried out with S. cerevisiae species or Candida sp. McCormick 28 showed that removal percentage is associated with the strain. Statistical analysis was focused on the strains that could remove over 50% of AFB 1 or Zn, showing that capability is also toxin-dependent (Fig. 2). The low linear regression rate (0.431) indicates that strains that can remove certain compounds are not necessarily capable of www.nature.com/scientificreports/ removing other toxins in the same way. However, the toxins tested in this experiment are chemically different, so this behaviour would vary depending on biochemical structure. Moreover, as can be seen from the results in Table 5, the percentage of AFB 1 bound by strains did not exceed 71.5%, whereas for Zn it was almost 99%. In addition, of all the strains tested, 39 were able to eliminate over 50% of the Zn present in the media, but fewer strains (33) were able to achieve the same level of decontamination with the AFB 1 -contaminated media. Based on these two findings, ANOVA analysis (p < 0.005) indicated that the number of groups with significant differences in the Zn detoxification test is greater than in the AFB 1 test.
Cell viability. All the strains tested were able to grow in contaminated MSM after 5 days at 30 °C. Generally, yeast counts indicated a concentration increase of 0.5-1 log unit at the end of the assay, i.e., showing the same amount of growth as the negative controls. However, certain strains, mostly from D. rugosa, were found to have a lower growth rate (0.1-0.2 log units) compared to the negative control (1 log unit; data not shown). The relationship between biomass growth and toxin elimination, as evaluated by linear regression analysis (0.003; 0.057), showed that toxin binding by yeast is not related to log unit increase (Fig. 3). Therefore, in general, the strains tested were not able to use the contaminated media for their development, which probably indicates www.nature.com/scientificreports/ that yeasts eliminate toxins by cellular adsorption. Aflatoxins are known to be diminished by physical binding rather than degradation in some microorganisms 29 and heavy metal bioremediation is normally carried out in yeast by bioaccumulation in the vacuoles 29 or by biosorption in cell walls 29,30 . In any case, the elimination mechanism of these strains should be studied thoroughly in future projects.
Biocontrol capability against mycotoxigenic moulds. The yeast strains that eliminated over 50% of the toxins, either AFB 1 or Zn, were grown on the same plate as a mycotoxigenic mould (A. parasiticus, F. graminearum, and P. crustrosum). Of all the strains (66) tested in this assay, 48.5% had varying intensities of biocontrol activity and were effective against at least one of the moulds (Table 6). Twenty-three of the strains affected the growth of A. parasiticus and these were AK11 (C. tropicalis), EW1 (K. pastoris), H1 (A. pullulans), EB35 (Rh. mucilaginosa), and ECF42 (C. parapsilopsis) strains. All of these strains reduced the mycelium by 50 to 60% and they showed significant differences from other strains. The activity presented against F. graminearum was weaker. Although 18 strains showed activity, only three presented over 50% inhibition, namely AK11 (C. tropicalis), EW3 (K. pastoris), and AS6 (Rh. mucilaginosa). Of these, AK11 showed the best results, with a reduction of 64.3%, and was classified in Table 5. Classification of the strains with detoxification capability > 50% of toxin removed (A: AFB 1 ; B: Zn; means ± SD). The different letters of the superscript indicate significant differences (p ≤ 0.05 per column). www.nature.com/scientificreports/ the group with the largest significant difference with respect to the negative control. An example of the mycelium inhibition of this mould is shown in Fig. 4. Only 11 of the strains were able to inhibit P. crustrosum. The best examples (over 50% inhibition) were ECF59, FR19 (D. rugosa), EB83 (S. cerevisiae), AB7 (Rh. mucilaginosa), and ECF42 (C. parapsilopsis) ( Table 6). Finally, in all cases, yeasts with biocontrol capability showed significant differences with respect to the negative controls. Some of the yeasts (ECF42-C. parapsilopsis, EW3-K. pastoris, and EB83-S. cerevisiae) showed inhibitory activity against the three moulds, albeit with different intensities. Biocontrol activity was assessed as another strain-dependent capability. Strains from the same species exhibited different behaviours against the three moulds, in varying intensities. C. albicans strains showed the same behaviour against these moulds, but strains from other species, such as K. pastoris, D. rugosa, and Rh. mucilaginosa, presented different levels of action against the mycotoxigenic moulds (Table 6). Studies have indicated that biocontrol activity in some microorganisms against others can be caused by competition for media nutrients or due to the antifungal secretions they produce in the media 28 . Zymocines produced by some species, such as S. cerevisiae and D. hansenii, are a common mechanism of action. These toxins provide a new tool that may be an alternative for synthetic fungicides 31−33 . The production of extracellular enzymes (β-glucanases and chitinases) by A. pullulans has proven to be an effective pathway against moulds 34 and this could be the reason why strain H1 showed this ability. A. pullulans has previously been used as a biocontrol agent for postharvest crop diseases  www.nature.com/scientificreports/ caused by Botrytis cinerea 35 . Furthermore, Sperandio et al. 36 found that an A. pullulans strain isolated from plants was capable of reducing the mycelium growth by 30-41.2%, a range of action similar to that observed in this article, although the mechanism of action could not be determined. Likewise, it has been reported that Rh. mucilaginosa strains isolated from peach blossoms reduce blue and grey mould decay on treated fruits, with an almost complete inhibition (97.2 and 97.1%) achieved when higher yeast cell concentrations (10 9 cells/mL) are used 37 . However, in this study, the Rh. mucilaginosa strain that showed the best biocontrol activity was adjusted to 10 6 cells/mL, and better results may be expected if a higher concentration is used. Other pieces of research have identified some species of Candida and Pichia sp, which, isolated from natural sources, presented biocontrol activity in vivo in fruit 33,34,38,39 .
In the study reported here, the AK11 (C. tropicalis) strain proved to have the best biocontrol activity against both A. parasiticus (57.4%) and F. graminearum (64.3%), although it did not have any effect on P. crustrosum growth. ECF59 (D. rugosa) showed the best mycelium reduction of P. crustrosum (68.3%) and it also reduced the growth of A. parasiticus by 44%, although it did not affect the Fusarium fungi.
Tolerance to the presence of Zn in solid media. In order to evaluate tolerance to Zn, the 66 strains that showed the best biodetoxification capability against both toxins were cultured in YM agar supplemented with different concentrations of Zn. After the incubation time, the samples were visually assessed and their growth identified as weak or strong. The results are provided in Fig. 5. Microbial growth occurred with up to 50 mg/L of Zn salt in 75% of the cases, and 53% of the yeasts tolerated the highest concentration (100 mg/L). As expected, all strains resisted the lower concentrations as they did in the detoxification assay. www.nature.com/scientificreports/ The results of these experiments are shown in Fig. 6. Strains with weak growth at 75 mg/L showed the same behaviour or zero growth at 100 mg/L, e.g., Rh. mucilaginosa. In contrast, strains with good growth at 75 mg/L were capable of resisting concentrations of 100 mg/L and showed a different development. The yeasts with the best behaviour (strong growth at 100 mg/L) were C. albicans, D. rugosa, K pastoris, P. kudriavzevii, and S. cerevisiae.
Muñoz et al. 40 published similar results for Rh. mucilaginosa, which could be the reason why its strains presented low biodetoxification activity against this heavy metal. Furthermore, some strains of D. rugosa such as FP5, which showed strong growth at 100 mg/L Zn, was able to almost completely eliminate (98.4%) the Zn present in the minimum salt medium, thus showing that tolerance to the ion is a key factor for biosorption. The only A. pullulans strain (H1) tested tolerated the highest Zn concentration, as documented previously 41 . Yeasts from the Pichia and Candida genus were also described as Zn-resistant and were able to tolerate up to 1.3 mg/L   44 reported that all tested yeast strains isolated from a coal mine were able to resist different concentrations of Zn. Although microorganisms isolated from contaminated environments tend to be more tolerant to these pollutants, other studies have indicated that there is very little difference in metal tolerance between strains from polluted and unpolluted sites 45 . Thus, the strains used in this experiment proved to have a good Zn tolerance, similar to those reported in other studies. Resistance to Zn by yeasts with good bioremediation capacity is important since this metal can be found in a wide range of concentrations in contaminated environments. Once again, the heterogeneity of the results showed that the response of the isolates to heavy metals essentially depended on the strain and the heavy metal concentration, as previously indicated by Muñoz et al. 40 .
In conclusion, the results reported here offer a protocol to ascertain the capability of wild yeasts for removing mycotoxins and heavy metals. It has been confirmed once again that microbial detoxification is strain-and toxin-dependent. The best performing species in regard to AFB 1 detoxification also showed biocontrol activity against A. parasiticus (H1-A. pullulans and EW1-K. pastoris). This finding, along with tolerance to Zn and its biodetoxification, could mean that some of the studied yeast strains will be of great interest for the treatment of contaminated environments, e.g. AK11 (C. pastoris), H1, EB39 (Rh. mucilaginosa), and EB83 (S. cerevisiae) among others. Finally, results obtained from the cell viability test supported the idea that other pathways, such as bioaccumulation or biosorption, may be used by yeast for eliminating contaminant compounds. Consequently, future studies will be carried out in this regard.