สำนักราชบัณฑิตยสภา

203 สมศั กดิ์ ด� ำรงค์เลิ ศ และคณะ วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๑ ม.ค.-มี.ค. ๒๕๕๕ methanol, 0.3 % H3PO4, and 49.7% water was used with the flow rate of 0.5 ml min -1 . The eluates were monitored by UV absorption at 275 nm. Concentration of AH2QDS were determined spectrophotometrically by monitoring the absorbance at 450 nm by using a molar extinction coefficient of 2.7 mM -1 cm -1 obtained from a calibration curve of AQDS chemically reduced by dithionite as previously described (10). Chemicals Remazol Brilliant Orange 3R, Remazol Black B, and Remazol Brilliant Violet 5R were kindly supplied by Dystar, Thailand, Ltd. NADH, FAD, ubiquinone (Q1), and menaquinone (MK) were purchased formSigma Chemical Co., St. Louis, Mo. AQDS, riboflavin, and humic acid were purchased from Aldrich Chemical (Milwaukee, Wis.). All other chemicals used for minimum medium and buffer solutions were obtained from E. Merck AG. (Darmstadt, Germany) and Aldrich Chemical (Milwaukee, Wis). RESULTS AQDS stimulation of different sulfonated azo dyes reduction by whole cells of strain A5 To determine whether AQDS stimulated bacterial azo dyes reduction, cell suspensions of azo dyes-reducing bacterium Paenibacillus sp. strain A5 were added to phosphate buffer containing glucose as the electron donor and various sulfonated azo dyes (for structural formulas see Fig. 1) and were incubated under anaerobic condi- tion. Cell suspensions of strain A5 only slowly reduced azo dyes in the absence of addi- tional redox mediator, but when the AQDS was also added to the buffer, azo dyes reduc- tion was greatly stimulated (Fig. 2). The observed variations in the relative increase of the azo dye reduction rates for different dyes were presumably due to differences in the redox potentials of the individual azo compounds. The lesser but significant stimulation was observed in this study with the commercially available Aldrich humic acids that was previously found to stimulate the dissimilatory reduction of ferric iron (31). Abiotic reduction of sulfonated azo dyes did not occur in controls without cells or added electron donor (Fig. 2).