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สารฮิ วมิ กช่วยเพิ่ มความสามารถการลดสี ... 210 The Journal of the Royal Institute of Thailand Vol. 37 No. 1 Jan.-Mar. 2012 in 10-h incubation period (Fig. 4). At the end of anaerobic incubation, the buffer turned orange owing to the accumulation of AH 2 QDS. The fact that the introduction of oxygen at the end of the anaerobic incubation resulted in immediate loss of orange color and decreased absorbance confirmed that AQDS was enzymatically reduced during the anaerobic incubation with strain A5 (data not shown). To evaluate the second reaction in proposed mechanism, sulfonated azo dyes were added into cell-free culture filtrates containing of AH 2 QDS, it was found that the orange color of AH 2 QDS disappeared immediately. Furthermore, it is evident that the amounts of three sulfonated azo dyes reduced rapidly and Remazol Brilliant Orange 3R and Remazol Brilliant Violet 5R were completely removed within a few minutes after addition into filtrates of 10-h anaerobic incubated cell suspensions containing 0.25 mMAQDS. In the other hand, AQDS not incubated with Paenibacillus sp. strain A5 did not reduced all sulfonated azo dyes and filtrates of cell suspensions that did not contain AQDS did not reduced all azo dyes. The addition of fixed concentration of all sulfonated azo dyes (0.1 mM) into the FIG. 4 Enzymatic reduction of AQDS to AH2QDS by Paenibacillus sp. strainA5 and subsequent chemical reduction of sulfonated azo dyes by AH2QDS. Washed cells of Paenibacillus sp. strain A5 (0.09gof protein l-1)were suspended in10ml.Na-Kphosphatebuffer (50mM; pH 7.5) containing glucose (5 mM) as the electron donor and AQDS (250 μM) as electron acceptor. The concentration of reduced AQDS (AH2QDS) was de- termined spectrophotometrically at 450 nm. After 10 h of anaerobic incubation, cells were removed by filtration (0.2-μM-pore-diameter filter). The cell-free culture supernatant was then filled into gas-tight cuvettes (final volume = 1 ml.) under anaerobic condition and anaerobic stock of each sulfonated azo dyes was added to 100 µ M final concentration. The cuvettes were transferred to a spectrophotometer and the decoloriza - tion of sulfonated azo dyes was determined at λ max of each azo dye.