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The influence of obligatory factors under static conditions, during decolourisation of remazol golden yellow by M. endophyticus ES37, was analysed using PBD. There was a wide variation in efficiency of remazol golden yellow decolourisation, ranging from 0.63 to 22.57% (Table 5). The statistical analyses of regression coefficients and estimated effects of the factors are given in Table 6. The coefficient values of yeast extract, pH and incubation period indicates that the increase in their concentration has a positive influence on the decolourisation process. Conversely, lower temperature, lactose concentration, inocula size and dye concentration are required to assist maximum dye removal ratio. Du et al. (2012) reported that yeast extract and pH had a positive effect on decolourisation of malachite green by Micrococcus sp. strain BD15, whereas a higher concentration of dye and higher temperature had negative effects on decolourisation; this supports the present observation. Anjaneya et al. (2011) pointed out that higher temperature leads to the loss of microbial metabolic activities during dye decolourisation. The necessity of using a lower concentration of dye and lactose in the culture medium may be related to the toxic effect on the bacterial cells, inhibition of azo reductase active sites and other enzyme systems involved in decolourisation (Tony et al. 2009; Jadhav et al. 2010). In the present study, factors possessing confidence levels greater than 90% were considered significant. A large t-value coupled with a low P-value specifies high significance of factors and model term.

Table 5

PBD of experimental and predicted decolourisation (%)

RunLactose %Yeast extract %TemperatureInoculum size %Dye concentrationIncubationPercentage decolourisation
order(w/v)(w/v)pH(°C)(v/v)(mg/L)period (h)ExperimentalPredicted
1.0 0.1 30 100 72 6.91 7.023 
1.0 1.0 45 100 24 7.28 7.89 
0.1 1.0 30 10 100 24 21.55 18.08 
1.0 0.1 45 300 24 4.88 3.7083 
1.0 1.0 45 10 100 72 8.17 7.56 
1.0 1.0 30 10 300 24 7.65 11.11 
0.1 1.0 45 300 72 22.57 20.56 
0.1 0.1 45 10 100 72 7.38 10.34 
0.1 0.1 45 10 300 24 1.64 1.79 
10 1.0 0.1 30 10 300 72 0.63 −1.85 
11 0.1 1.0 30 300 72 13.34 15.32 
12 0.1 0.1 30 100 24 5.08 5.43 
RunLactose %Yeast extract %TemperatureInoculum size %Dye concentrationIncubationPercentage decolourisation
order(w/v)(w/v)pH(°C)(v/v)(mg/L)period (h)ExperimentalPredicted
1.0 0.1 30 100 72 6.91 7.023 
1.0 1.0 45 100 24 7.28 7.89 
0.1 1.0 30 10 100 24 21.55 18.08 
1.0 0.1 45 300 24 4.88 3.7083 
1.0 1.0 45 10 100 72 8.17 7.56 
1.0 1.0 30 10 300 24 7.65 11.11 
0.1 1.0 45 300 72 22.57 20.56 
0.1 0.1 45 10 100 72 7.38 10.34 
0.1 0.1 45 10 300 24 1.64 1.79 
10 1.0 0.1 30 10 300 72 0.63 −1.85 
11 0.1 1.0 30 300 72 13.34 15.32 
12 0.1 0.1 30 100 24 5.08 5.43 
Table 6

Estimated effects of PBD

S. no.VariableEffectCoef.SE coef.TP
Constant – 8.916 1.011 8.82 0.001* 
Lactose −6.018 −3.009 1.011 −2.98 0.041* 
Yeast extract 9.015 4.507 1.011 4.46 0.011* 
pH 5.782 2.891 1.011 2.86 0.046* 
Temperature −0.545 −0.272 1.011 −0.27 0.801 
Inoculum size −2.152 −1.076 1.011 −1.06 0.347 
Dye concentration −0.948 −0.474 1.011 −0.47 0.663 
Incubation period 1.822 0.911 1.011 0.90 0.418 
S. no.VariableEffectCoef.SE coef.TP
Constant – 8.916 1.011 8.82 0.001* 
Lactose −6.018 −3.009 1.011 −2.98 0.041* 
Yeast extract 9.015 4.507 1.011 4.46 0.011* 
pH 5.782 2.891 1.011 2.86 0.046* 
Temperature −0.545 −0.272 1.011 −0.27 0.801 
Inoculum size −2.152 −1.076 1.011 −1.06 0.347 
Dye concentration −0.948 −0.474 1.011 −0.47 0.663 
Incubation period 1.822 0.911 1.011 0.90 0.418 

*Significant.

R2 = 90.74% R2(adj) = 74.53%.

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