Biodegradation Of Azo Dyes By Fungi Other Than White Rot Fungi

In recent years there have been many reports regarding biodegradation of azo dyes by white rot fungi (Bumpus 1995; Stolz 2001; Yuzhu and Viraraghavan 2001; Knapp et al. 2001; Robinson et al. 2001; McMullan et al. 2001). In contrast, there have been only a few reports focusing on biodegradation and/or decolorization of azo dyes by fungi that are not white rot fungi. Some of these fungi are listed in Table 2.

Table 2 Manuscripts describing adsorption of or biodegradation of azo dyes by fungi other than white rot fungi

Fungus

Dye

Reference

N. crassa

Vermelho Reanil P8B

Corso et al. (1981)

A. sojae B-10

Amaranth, Sudan II, Congo Red

Behung-Ho and Weon (1992)

A. foetidus

Drimarene Red, Drimarene Blue

Sumanthi and Phatak (1999)

Drimarene Black

Sumanthi and Manju (2000)

C. inaequalis

Chicago Sky Blue 6B

ten Brink et al. (2000)

As noted by Chung and Stevens (1993) an early report by Riedel (1942) showed that azo dyes were reduced by yeasts but that pure culture isolations were not reported in this study. In a study focusing on the use of fungi to treat industrial effluents containing an azo dye it was shown by Corso et al. (1981) that the Ascomycete Neurospora crassa was able to decolorize water containing Vermelho Reanil P8B. In these studies 91.3-89.1% decolorization was achieved during a 24-hr incubation period in water in which the dye concentration was 16-32mg/L. These dye concentrations are typical of those that would be found in wastewater. Behung-ho and Weon (1992) reported that the Ascomycete Aspergillus sojae B-10 was able to mediate substantial decolorization of Amaranth, Sudan III, and Congo Red. The effect of several nutrient nitrogen sources on decolorization was assessed. Nitrogen containing salts (ammonium tartrate, sodium nitrate, ammonium nitrate, and ammonium sulfate) appeared to promote decolorization relative to biologically derived nitrogen sources (peptone, malt extract, and yeast extract). It was also shown that decolorization decreased as a function of sodium nitrate concentration for all three dyes that were studied. Adsorption contributed to the decolorization that was observed. However, the authors assert that biodegradation was also important in this process. If this decolorization is, indeed, due to biodegradation and not simple adsorption it will be interesting to determine the mechanisms by which biodegradation occurs as they will almost certainly be different than those which occur in white rot fungi.

Sumanthi and Phatak (1999) and Sumanthi and Manju (2000) showed that Aspergillus foetidus was able to decolorize in culture several azo dyes (Remazol Red, Remazol Dark Blue HR, Remazol Brown GK, Drimarene Red, Drimarene Blue, Drimarene Black, Procion Green, and Procion Turquoise). However, these investigators noted that decolorization was due primarily to biosorption and that little biotransformation occurred.

Curvularia spp. are members of the Ascomyctes and include animal and plant pathogens. Unlike the other fungi discussed in this review, Curvularia inaequalis produces a peroxidase that contains vanadate rather than heme (ten Brink et al. 2000). This vanadium containing peroxidase requires hydrogen peroxide as a cosubstrate and mediates oxidation of halides to hypohalous acid. It also mediates the sulfoxidation of organic sulfides to sulfoxides and the one-electron oxidation of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) to its free radical product (ten Brink et al. 2000). It has been shown that the vanadate-containing peroxidase from this fungus mediates oxidation of the azo dye Chicago Sky Blue 6B (ten Brink et al. 2000).

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