3.2. Toxicity response against various metals
The variations in MIC values suggest that the resistance level against individual metals is different. This could be related to varied toxicity responses of A. lentulus to different metals. Metal specific changes in the growth pattern and morphology were clearly observed. Although all the metals caused the growth inhibition at respective concentrations, the response of the organism in terms of pellet morphology was quite different. While in presence of Cu(II), the diameter of the pellet increased from 0.5 mm (control) to 4–6 mm (800 mg L−1 Cu(II) concentration). Such an increment in the size was not observed in the presence of Ni and Cr(III). Earlier, our results have demonstrated that the enhancement in the pellet size due to mycelia aggregation is a typical response by the fungus to avoid metal toxicity against Cr(VI). The pellets those fail to aggregate are unable to bear the metal toxicity resulting in death ( Sharma et al., 2009). Thus, it seems that changed morphology supports higher MIC of toxic metals. On the other hand, in the presence of lead ions, mycelium became ruptured. It appeared like a ball with solid core and a few filaments protruding out from the outer shell. This was different from smooth surface of the pellets, as observed in the presence of other metals.
The SEM micrographs depicted a clear distinction between the control (Fig. 1A) and metal stressed mycelia (Fig. 1B–E). The long, ribbon like fungal hyphae in the control pellets were uniformly shaped and loosely packed, resulting in small pellets but with fluffy and porous structure (Fig. 1A). However, in the presence of metals, mycelia appeared short, dense and broken. In response to Ni(II), decreased mycelial length was very much evident (Fig. 1E). Twisting and looping of individual hyphae and the formation of tightly packed intertwined hyphal strands was observed in response to Cr(III) and Cu(II) stress (Fig. 1B–C). Further, the mycelia were more deformed and had a higher tendency to aggregate in the presence of Pb(II) ions (Fig. 1D). It seems to be a toxicity response of the organism that might reduce the surface area exposed to toxic metal. Lilly et al. (1992) also observed the twisting and looping of individual hyphae and the formation of intertwined hyphal strands in response to metal stress.
3.2. Toxicity response against various metalsThe variations in MIC values suggest that the resistance level against individual metals is different. This could be related to varied toxicity responses of A. lentulus to different metals. Metal specific changes in the growth pattern and morphology were clearly observed. Although all the metals caused the growth inhibition at respective concentrations, the response of the organism in terms of pellet morphology was quite different. While in presence of Cu(II), the diameter of the pellet increased from 0.5 mm (control) to 4–6 mm (800 mg L−1 Cu(II) concentration). Such an increment in the size was not observed in the presence of Ni and Cr(III). Earlier, our results have demonstrated that the enhancement in the pellet size due to mycelia aggregation is a typical response by the fungus to avoid metal toxicity against Cr(VI). The pellets those fail to aggregate are unable to bear the metal toxicity resulting in death ( Sharma et al., 2009). Thus, it seems that changed morphology supports higher MIC of toxic metals. On the other hand, in the presence of lead ions, mycelium became ruptured. It appeared like a ball with solid core and a few filaments protruding out from the outer shell. This was different from smooth surface of the pellets, as observed in the presence of other metals.The SEM micrographs depicted a clear distinction between the control (Fig. 1A) and metal stressed mycelia (Fig. 1B–E). The long, ribbon like fungal hyphae in the control pellets were uniformly shaped and loosely packed, resulting in small pellets but with fluffy and porous structure (Fig. 1A). However, in the presence of metals, mycelia appeared short, dense and broken. In response to Ni(II), decreased mycelial length was very much evident (Fig. 1E). Twisting and looping of individual hyphae and the formation of tightly packed intertwined hyphal strands was observed in response to Cr(III) and Cu(II) stress (Fig. 1B–C). Further, the mycelia were more deformed and had a higher tendency to aggregate in the presence of Pb(II) ions (Fig. 1D). It seems to be a toxicity response of the organism that might reduce the surface area exposed to toxic metal. Lilly et al. (1992) also observed the twisting and looping of individual hyphae and the formation of intertwined hyphal strands in response to metal stress.
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