TABLE 2.

Effect of humic acids on the pattern of products of glucose fermentation by various bacteria^a

Species	Humic acidsb	Ferric ironc	Concn of substrate consumed (mM)	Concn of products formed (mM)							Electron recovery (%)d
				Lactate	Succinate	Acetate	Propionate	Ethanol	Formate	Fe2+
E. cecorum	−	−	5.0	8.2		0.6		2.7	2.8	NDe	117 ± 3.5
	+	−	5.0	6.2		1.5			3.0	ND	77 ± 11.3
L. lactis	−	−	5.0	11.0						ND	110 ± 1.4
	+	−	5.0	6.7		0.9				ND	73 ± 1.4
	+	+	3.0	3.6		0.9				6.3	79 ± 4.3
E. coli	−	−	3.0	2.4	0.8	1.0		1.1	0.1	ND	83 ± 5.5
	+	−	3.0	2.5	0.8	0.8		1.1	0.1	ND	84 ± 3.4

^aAll values are averages of values from two separate cultures, which were determined 7 days after inoculation. For reasons of clarity, standard deviations are reported only for electron recovery. The detection limit for fermentation products was 0.1 mM. 

^bHumic acids were obtained from Aldrich (concentration, 20 mg ml⁻¹). 

^cAmorphous ferric iron (concentration, 40 mM). 

^dThe amounts of electrons recovered in the products were compared to the amounts of electrons in the substrate consumed. 

^eND, not determined.