The effects of CO2 and H2 on CO metabolism by pure and mixed microbial cultures

Table 2 Electron equivalents in substrates and products, along with ethanol-to-acetate ratios, in the fermentation of CO and CO with H₂ and/or CO₂ by the CO-consuming cultures

CO-consuming culture	Gas mixture	Initial P_CO, kPa	Initial P_CO2, kPa	Initial P_H2, kPa	Electrons in susbtrate^*, e⁻ meq.	Initial C:e⁻ ratio, mmol/e⁻ meq.	H₂, e⁻ meq.	Ethanol/acetate, e⁻ meq./e⁻ meq.	CO consumption rate^**, mmol CO L⁻¹ day⁻¹
CO-enriched mixed culture	CO	0^a	0	0	21.0^b	–	0.1	0.12 - 0.3	3.4
		0^a	0	0	48.2^c	–	0	–^d	7.1
		31.4	0	0	4.1 ± 0.1	0.5	0.04	0.14 ± 0.03	3.5
	CO: H₂	31.4	0	96.2	9.4 ± 0.3	0.2	0	0.03 ± 0.01	2.4
	CO: CO₂	32.4	32.4	0	4.1 ± 0.0	0.7	0.2 ± 0.1	0.03 ± 0.03	2.5
	CO: CO₂: H₂	32.4	15.2	16.2	6.7	0.5	0	0.06 ± 0.03	2.1
Acetobacterium-like isolate	CO	30.4	0	0	4.1 ± 0.1	0.5	1.8 ± 0.3	14.2 ± 5.2	1.4
	CO:YE	30.4	0	0	6.0 ± 0.0	0.3	1.0 ± 0.01	400 ± 133.3	1.8
	CO:H₂	30.4	0	92.2	9.4 ± 0.3	0.2	1.3 ± 0.1	11.2 ± 0.5	0.7
	CO:CO₂	30.4	31.4	0	4.1 ± 0.0	0.7	0.5 ± 0.3	0.86 ± 0.01	1.4
	CO:CO₂:H₂	31.4	15.2	17.2	5.8	0.5	2.5 ± 0.3	2.5 ± 0.25	5.0
Pleomorphomonas-like isolate	CO	31.4	0	0	4.1 ± 0.1	0.5	3.2 ± 0.2	–	1.0
	CO: YE	29.4	0	0	4.7 ± 0.1	0.3	3.8 ± 0.3	–	1.3
	CO: H₂	30.4	0	95.2	9.4 ± 0.3	0.2	7.1 ± 0.15	–	0.7
	CO: CO₂	28.4	30.4	0	4.1 ± 0.1	0.7	0.0	–	0.0
	CO: CO₂:H₂	30.4	15.2	18.2	3.4 ± 0.04	0.5	1.0 ± 0.3	–	1.1

* Electrons added as CO and/or H₂, and organic matter (i.e., fatty acids in inoculum)
** Maximum rates achieved during exponential CO consumption in serum bottles, and estimated rates in the batch reactor
^aInitial P_CO in batch reactor with continuous CO supply is 0 kPa, since CO gradually diffuses through the membranes, and only CO not consumed by the biofilm formed on the membranes ends in the headspace of the reactor
^bAfter 55 days of fermentation, at P_CO = 12.16 kPa
^cAfter 61 days of fermentation, at P_CO = 4.05 kPa
^dNo acetate detected, and 69.5 ± 3.1 mM (40.6 e⁻ meq.) of ethanol produced

ISSN: 2731-3654