fermentation. From these results, it was confirmed that the
coproduction of electricity did not affect the acetic acid yield. Acetic
acid productivity increased with the number of repeated batch
fermentations completed (Table S1). During the repeated batch
fermentation, an A. aceti biofilmwas formed on the anode electrode
surface. This biofilm might have enhanced the acetic acid productivity
by increasing the number of cells and the cell density around
the electrode, allowing easier access to the electrode. A smaller
acetic acid yield was observed in the third batch fermentation than
was observed in the second batch fermentation, which might have
resulted from activation of an A. aceti metabolic pathway following
the ethanol oxidation to acetic acid during the long fermentations.
The acetic acid productivities in all of the batches were over 20-fold
smaller than that observed in the aerated fermentation. Because
the first batch fermentation in the MFC and the aerated fermentation
contained the same concentration of A. aceti cells in the
fermentation suspension, this difference did not result from the
quantity of microbial cell catalyst available to convert ethanol to
acetic acid. The difference in the accessibility parameters and the
relative ease of accepting electrons from A. aceti cells between the
dissolved oxygen and the carbon anode electrode surface might
have caused this result. The Coulombic efficiencies obtained in this
study were small compared with that previously reported for an
MFC with A. aceti using ethanol as the substrate (14). The pyrroloquinoline
quinone (PQQ) located on the periplasmic membrane
of acetic acid bacteria acts as an electron transfer mediator (19).
Low Coulombic efficiencies might result from insufficient electron
transfer from PQQ to the anode. From investigations into the
improvement of MFC performance, it is well-known that several
fermentation. From these results, it was confirmed that thecoproduction of electricity did not affect the acetic acid yield. Aceticacid productivity increased with the number of repeated batchfermentations completed (Table S1). During the repeated batchfermentation, an A. aceti biofilmwas formed on the anode electrodesurface. This biofilm might have enhanced the acetic acid productivityby increasing the number of cells and the cell density aroundthe electrode, allowing easier access to the electrode. A smalleracetic acid yield was observed in the third batch fermentation thanwas observed in the second batch fermentation, which might haveresulted from activation of an A. aceti metabolic pathway followingthe ethanol oxidation to acetic acid during the long fermentations.The acetic acid productivities in all of the batches were over 20-foldsmaller than that observed in the aerated fermentation. Becausethe first batch fermentation in the MFC and the aerated fermentationcontained the same concentration of A. aceti cells in thefermentation suspension, this difference did not result from thequantity of microbial cell catalyst available to convert ethanol toacetic acid. The difference in the accessibility parameters and therelative ease of accepting electrons from A. aceti cells between thedissolved oxygen and the carbon anode electrode surface mighthave caused this result. The Coulombic efficiencies obtained in thisstudy were small compared with that previously reported for an
MFC with A. aceti using ethanol as the substrate (14). The pyrroloquinoline
quinone (PQQ) located on the periplasmic membrane
of acetic acid bacteria acts as an electron transfer mediator (19).
Low Coulombic efficiencies might result from insufficient electron
transfer from PQQ to the anode. From investigations into the
improvement of MFC performance, it is well-known that several
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