Congo Red Decolorizing Bacteria from Paper Factory Effluent - Microbial Degradation of Synthetic Dyes in Wastewaters - page 137

0.3 ml phenylmethylsulfonyl uoride (PMSF) and then the cells were sonicated in

ice for 20 min at rest intervals of 1 min. The sonicated cells were centrifuged for
10 min at 10,000 rpm at 5

C and after which the supernatant or cell-free extract
(CFE) was collected (Barraquio 1992 ) and tested for decolorization. Qualitative
analysis of dye decolorization was done using the spectrophotometer and based on
the disappearance of the color.
It was observed that dye degradation occurred in the supernatant of the sonicated
cells of the monocultures incubated with Congo red. In the case of the

°

lter ster-
ilized culture broth with Congo red, no decolorization occurred even after several
months of incubation, indicating that the enzyme responsible for the reduction of
Congo red is located intracellularly. This could also explain why the number of
cells decreased as Congo red decolorization progressed over time (Fig. 5 ). Over
time, the cells become aged and lyze and the enzyme inside the cell goes out into
the medium which interacts with the dye to reduce it. This was found to be true for
all the four (4) Congo red decolorizing bacteria. The cell membrane of bacteria is
not permeable to sulfonated azo dyes, such as Congo red. This is why reduction of
highly polar dyes is usually postulated to take place outside the cell (Stolz 2001 ).
Most investigators, who studied the reduction of azo dyes by bacteria, observed
the extreme lack of speci city of the azo reductase system and showed that cell

extract or aged (damaged) cells reduced azo dyes more ef ciently and metabolized a

wider range of azo dyes than intact cells (Dickhues 1960 ; Wurhmann et al. 1980 ;
Mechsner and Wuhrmann 1982 ). The azo reductase from Clostridium perfringens

Fig. 5 Rate of Congo red decolorization and growth of cells over time