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สารฮิ วมิ กช่วยเพิ่ มความสามารถการลดสี ... 216 The Journal of the Royal Institute of Thailand Vol. 37 No. 1 Jan.-Mar. 2012 ployed to demonstrate that, though the use of redox mediator such as AQDS, direct con- tact between azo dye and microbial cells is not required, which allows microbial activity to decoupled in space and time from azo dyes reduction process. For example, a sys- tem of two separated columns which one used for redox mediator reduction and the an- other one use for azo dye reduction has been set up for stimulation of azo dye reduction by Burkholderia cepacia (30). Alternatively, the laboratory-scale upflow anaerobic sludge bed (UASB) containing activated carbon as an immobilized quinoid redox mediator in the sludge bed has been tested for its accelerating effect on anaerobic reduction of a recalcitrant azo dye (54). The fact that exogenous extracellular molecules (such as humic substances) can participate in electron transfer to extracellular environmental contaminants indicates that they may make a significant contribution to biotransformation of such xenobiotics in many environments (7, 10, 11). Whether microbially produced extracellular molecules have a similar role remains an important question. Another possibility for the reduction of extracellular quinoide redox mediator such AQDS, which does not require the transport of both redox mediators and azo dyes though the cell membrane, has been suggested for humate-respiring bacterium, Shewanella putrefaciens (34). Non-proteinaceous small compound that has characteristics similar to a quinone and can be excreted into the medium is involved in electron transfer to AQDS and humic acid by this strain (34). More- over, a derivative of 1,4-dihydroxy-2-naphthoate (DHNA), precursor of menaquinone, is responsible for the carbon tetrachloride transformation activity observed in Shewanella oneidensis MR-1 after aerobic growth (55). Menaquinone (MK) is the only common link for the different electron transfer routes in B. subtilis, and it is tempting to propose that MK itself can be the component whose reduction-oxidation is controlled by energization (34). Because the rather high reduction rate of sulfonated azo dyes in the absence of any exogenous redox mediators found in whole cells experiment (Fig. 2 and Table 3), we cannot eliminate the possibility that some unknown enzymatic activities are involved in the anaerobic reduction of sulfonated azo dyes by whole cells of strain A5. We are currently attempting to explore the other extracellular electron transferring mechanisms of strain A5 which are involved for the reduction of the AQDS to clarify this mechanism.