TABLE 2.

Quantification of substrates consumed and products formed during growth of strain EbS7 with ethylbenzene^a

Expt	Amt of ethylbenzene added (μmol)	Amt of ethylbenzene that disappeared (μmol)b	Amt of sulfate that disappeared (μmol)	Amt of 4-phenyl- pentanoate formed (μmol)	Amt of cell dry mass formed (mg)c	Amt of electrons available for sulfate reduction (μmol)d	Amt of electrons consumed by sulfate reduction (μmol)e	Electron balancef
Cells with limiting amount of ethylbenzene	44	44	223	1.5	1.4	1,628	1,520	1.07/1
Cells with excess ethylbenzene	244	168	683	27.4	3.8	5,042	5,200	0.97/1
Cells without ethylbenzene (control)	0	0	33	1.1	<0.2
Sterile medium without cells	242.6	0	0	0

^aIncubation experiments (separate from the growth experiment whose results are shown in Fig. 4) were carried out in anoxic flat bottles with a culture volume of 70 ml. The medium was overlaid with 2 ml of HMN as the carrier phase for ethylbenzene.

^bDifference between the amount of ethylbenzene added and the amount of ethylbenzene recovered at the end of incubation in the carrier phase and the aqueous phase.

^cThe amount of cell dry mass was determined by measuring the amount of protein, assuming that the protein accounted for 50% (wt/wt) of the dry mass. The amount of cell mass present at the beginning of the experiment was subtracted.

^dThe electrons available for sulfate reduction were the electrons derived from consumed ethylbenzene, corrected by subtraction of the electrons present in the 4-phenylpentanoate excreted and the cell mass formed. Stoichiometrically, 1 mol of ethylbenzene corresponds to 42 mol of electrons, whereas 1 mol of 4-phenylpentanoate corresponds to 54 mol of electrons. One milligram (dry weight) of cells (approximate net formula, C₄H₇O₃) contains 165 μmol of electrons. Before calculation of the electrons available for sulfate reduction, the values for 4-phenylpentanoate and cell dry mass were corrected by subtraction of the corresponding values obtained for the control without ethylbenzene.

^eStoichiometrically, 8 mol of electrons is required for reduction of 1 mol of SO₄²⁻ to H₂S. The correct amount of sulfate reduced was obtained by subtraction of the amount consumed in the control without ethylbenzene.

^fRatio of the amount of electrons from dissimilated ethylbenzene to the amount of electrons consumed by sulfate reduction.