731 Table 12- Initial pH of BR-Vogel’s medium plates, and estimated sodium chloride content (as halite). Sample Parameter Bauxite residue concentration 0 2 4 5 6 8 10 15 20 25 30 35 40 Control pH 5.7 NaCl % - BR-A pH 7.4 7.6 7.7 7.8 8.3 8.4 8.5 8.6 NaCl % 0.09 0.18 0.27 0.36 0.45 0.54 0.63 0.72 BR-B pH 7.7 8.0 8.4 8.6 8.8 NaCl % - - - - - BR-C pH 7.7 7.9 8.2 8.4 8.6 8.7 8.7 8.9 NaCl % 0.59 1.18 1.78 2.37 2.96 3.55 4.14 4.74 2.5 Inoculation And Growth Measurement Solid cultures were inoculated with 1 × 10⁵ spores from spore suspensions of A. niger and P. oxalicum by placing them on a sterile inoculation disk positioned at the center of the plate. Plates were incubated in the dark at 30 °C. Linear growth was evaluated by measuring colony diameter daily. A. niger cultures were monitored for 11 days to assess pH, salinity, and BR tolerance, whereas P. oxalicum cultures were evaluated for 18 days for BR tolerance and 11 days for pH and salinity tests. The tolerance index (TI) was calculated by dividing the diameter of fungal growth under the tested condition by the diameter of growth on the control plate, following previously described methodology (Table 13) (Rose & Devi, 2018). Mean growth diameters across conditions within each Vogel’s minimal agar treatment were compared using one-way ANOVA, with post-hoc significance assessed by Tukey’s HSD test (a = 0.05). Table 13- Tolerance index ranges and definition. Tolerance Index Definition TI > 1 Overtolerance or stimulation TI = 1 Neutral 0.8 < TI < 0.99 High tolerance 0.5 < TI < 0.79 Moderate inhibition TI < 0.5 Severe inhibition TI = 0 Complete inhibition 3. RESULTS AND DISCUSSION 3.1 Effect Of Ph And Salinity On The Growth Of The Selected Fungal Strains At pH 7, A. niger showed no inhibition, and its mean linear growth was statistically similar to the control ( Figure 47.A). A slight but significant inhibitory effect occurred at pH 8 and pH 9 compared to the control, with tolerance indices of 0.98, and 0.98, respectively. At pH 10, the tolerance index dropped to 0.89, indicating high tolerance but significantly reduced growth. However, growth was completely inhibited under more alkaline conditions. These findings align with previous reports showing that this strain can grow within a pH range of 1.4-9.8 (Upton, McQueen-Mason, & Wood, 2017). P. oxalicum maintained high tolerance from pH 7 to 10, with tolerance indices ranging from 0.99 to 0.88, and optimal growth at pH 7 (
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