Congo Red Decolorizing Bacteria from Paper Factory Effluent - Microbial Degradation of Synthetic Dyes in Wastewaters - page 139

the highest point or apex of the plant shoot. Dry weights, were determined by
drying whole plants in an oven at 50 C until constant weight was obtained.

The growth of bacteria and yeast was not inhibited by both the consortium-
decolorized medium and monoculture decolorized medium as shown by the
absence of zones of inhibition on 24

°

48 h-old lawn of microorganisms. This
indicates that bacterial decolorization of Congo red did not result in metabolic
products which were more toxic than the dye. The undegraded Congo red (positive
control) also did not affect the growth of the microbes. Thus, these microbes have
an inherent resistance to the toxic effects of the undegraded Congo red. This
inherent resistance to diazo dye may not hold true for all microbes since some might
be sensitive to this toxic dye.
However, the effects of undegraded Congo red and the decolorized culture
medium on the plants were different from that on bacteria and yeast. Figure 6 shows
that rice seedlings, soaked in denitrifying consortium-decolorized medium obtained
on the 14th day of incubation (T2), have higher plant shoots as compared to
seedlings exposed to decolorized

-

ltrate on the 7th day of incubation (T1), in
Fahreus medium (T3), and 1 % Congo red solution (T4). Therefore, higher dry
weight of rice seedlings was obtained.
Overnight soaking of selected rice seedlings in nitrate reducing monoculture
decolorized medium obtained on the 7th day of incubation, resulted in the highest
plant shoots as compared to seedlings soaked in decolorized medium derived on the
14th day of incubation, Fahreus medium and 1 % Congo red solution. Rice seed-
lings soaked in 1 % Congo red solution resulted in the lowest shoot heights (Fig. 7 )

Fig. 6 Effect of denitrifying consortium-decolorized medium on growth of rice shoots. The bars
are the averages of three replicates from each treatment, and error bars indicate ± standard
deviations from the means. Treatments used were T1 Denitrifying consortium-decolorized medium
on 7th day of incubation, T2 Denitrifying consortium decolorized medium on 14th day of
incubation, T3 Fahreus medium (negative control) and T4 1 % Congo red solution (positive control)