During the study on effect of enzyme dose concentration, on decolorization of malachite green (100mg/L), decolorization rate increases gradually from 10 – 30U/ml, with almost compete decolorization within 8h of incubation.
On increasing the dye dose to 40 U/ml decolourization rate doesn’t increased. Sharma et al. 2014 also reported similar results with respect to enzyme dose. Comparable to our results Murugsen et al. 2007 also reported complete decolorization of malachite green (100mg/L) with 30U/ml of dye dose within 16h.Effect of dye concentration on decolorization of malachite green by laccaseWhile studying the effects of dye concentrations (100 – 500 m/L) on decolorization of malachite green with 30U/ml, it was found that on increasing the dye concentrations, decolorization rate as slow in the beginning, but increases gradually with incubation time and at a certain point reaches to a constant stage, 100 and 200mg/L of malachite green completely decolorized within 12h and 28h respectively, while higher enzyme concentration of 300, 400 and 500mg/l were decolorized to 73, 64 and 57% in 24,28 and 32 h respectively. Our results are comparable with the results of Sharma et al 2014.
From the result it was found that at higher dye concentration efficiency of the enzyme get reduced (Satishkumar et al., 2010). Evaluation of malachite green toxicity towards fungiAmong the six fungal cultures tested for evaluating the toxicity of malachite green, Lepiota sp turns to be more sensitive to malachite green with no growth at any of the dye concentrations (Table) Toxicity of malachite green toward many fungi have been shown by many other workers namely (Maalej et al. 2009, Papinutti et al. 2006; Satishkumar et al 2010) species namely, P.
chrysosporium and Trametes sp.Fungal viabilityThe radial growth of the fungal mycelium of Ganooderma gibbosum and Lentinus sajor – caju supplemented with laccase pretreated dye was more on MEA supplemented with laccase treated dye compared to untreated, but less when compared with controls (Table). From the data it can be concluded that media supplemented with laccase treated dye of both fungi, making it amenable for the growth of fungi.
It was observed that growth of all the isolates was found to be more on MEA supplement with laccase treated dye. However Peniophora, Lepiota sp and Pleurotus sp were found to be more sensitive to malachite green at higher dose in both laccase treated MEA and untreated. The laccase pretreated dyes from Ganoderma gibbosum and Lentinus sajor – caju at all the concentrations gets nearly completely decolorized, while at dye concentration of more than 200mg/l growth was inhibited supplemented with pretreated dyes compared to control, but more than media with untreated dye (Table). Like our results Parshetti et al.
, 2006 also reported that rate of decolorization was decreased with increasing the dye concentration of MG. Only about 13% and 6% decolorization was observed from Kocuria rosea laccase at 70 and 100mg/l dye concentration respectively. These results indicate toxicity of malachite green at higher dose concentrations.
Results about biodegradation of malachite green by Sphingomonas paucimobilis decolorization decreased on increasing the dye concentration. In our research work we also found that efficiency of decolorization of malachite green by G. gibbosum and L.
sajor- caju was reduced by increasing the concentration of dye (Fig). Ganoderma gibbosum showed 73, 64 and 57% of 300,400 and 500 mg/L of malachite green that may be due to the fact that on increasing the dye concentration efficiency of the enzyme get reduced (Satishkumar et al., 2010). Maalej – Kammoun et al (2009), Sharma et al.
, 2014 also showed removal of malachite green toxicity after laccase treatment while Satish Kumar et al.,2010 reported reduced phytotoxicity of malachite green after laccase treatment.Evaluation of malachite green toxicityAmong the six fungal isolates tested, Lepiota sp, Peniophora sp, and Pleurotus sp turns to be more sensitive to malachite green. Malachite green is one of the most abundantly available dye that is most commonly used for coloring materials such as cotton, wood silk, leather, jute etc (Murugesan et al., 2009; Srivastava et al., 2004), also used in aqua culture and fisheries as antiparasitic and antifungal, antibacterial agents (Daneshwar et al., 2007; Srivastava et al.
, 2004). Due to toxic effect on wide range of aquatic and terrestrial animals even also on human health, even at very low concentration (1mg/l) (Helme et al.,2007) that can lead to malignant cell formation (Azmi et al., 1998) also promote hepatic tumor formation in rodents and also causes reproductive abnormalities in rabbits (Fernandes et al 1991; Rao 1995). As a consequence, extensive research in this field is carried out in order to remove the MG from aqueous solution as well its degradation from the environment because it is environment persistant dye. In the present study six fungal isolates have been investigated for their capability to remove MG. The two most interesting strains, identified by molecular technique were used for further study focused on decolorization. To overcome the toxic effect the use of MG in several countries have band by the govt of world, but it is still used in many countries due to its low cost and readily availability especially in aquacultures industries for controlling fungal infections and ectoparasites.
Variety of white rot fungi (Phanerochaete chrysosporium, Coriolus versicolor, Fomes sclerodermeus) (Levin et al, 2004; Papinutti and Forchiassin 2004); Ganoderma sp. rckk-02 (Sharma et al. 2013), P. cinnabarinus (Eggert et al.
1997) and P. chrysosporium (Srinivasan et al. 1995), are known producers of laccase that are studied with the view of dye decolorization as they are known laccase producers and they are more efficient in dye decolorization.