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Figure 1. 

Scheme and photo of the electrified Pioreactor® in a two-electrode one-chamber configuration with optional feed and bleed appliance.

Figure 2. 

Scheme and photo of the electrified Pioreactor® in a three-electrode two-chamber configuration.

Figure 3. 

Continuous cultivation in the two-electrode Pioreactor®. C. necator ΔPHB was cultivated in the electrified Pioreactor® under electro-autotrophic conditions in minimal medium at 30 °C and 500 r/min for 9 d. The reactors were supplied with a gas mixture of N₂ : CO₂ : O₂ (85:10:5) at a flow rate of 30 mL/min. A current of 3 mA was applied for the water splitting reaction; the resulting voltage (blue) lay around 2.7 V after inoculation. The reactors were inoculated at an OD₆₀₀ (red) of 0.2 and kept at 1 as soon as they reached it. The feed volume is shown as a black line (n = 2).

Figure 4. 

Characterization under heterotrophic conditions of the Pioreactor® adapted C. necator ΔPHB adePio compared to the wild-type strain. C. necator ΔPHB (black) and C. necator ΔPHB adePio (red) were cultivated in a 96-well plate in the Stratus Cerillo microplate reader in minimal medium with (a) 0, (b) 100, (c) 200, (d) 300, (e) 400, and (f) 500 mM sodium sulphate at 30 °C and 500 r/min for 48 h, n = 6.

Figure 5. 

Characterization under electro-autotrophic conditions of the Pioreactor® adapted C. necator ΔPHB adePio compared to the wild-type strain. C. necator ΔPHB (black) and C. necator ΔPHB adePio (red) were cultivated under electro-autotrophic conditions in minimal medium with 300 mM sodium sulphate at 30 °C and 300 r/min for 7.5 d. The reactors were supplied with a gas mixture of N₂ : CO₂ : O₂ (85:10:5) at a flow rate of 25 mL/min. A current of 15 mA was applied for the water splitting reaction. Shown are the (a) OD₆₀₀ and growth rate h⁻¹, as well as (b) the measured voltage (n = 3).

Figure 6. 

Batch cultivation in the three-electrode Pioreactor®. C. necator H16 was cultivated in the electrified Pioreactor® in minimal medium with 5 mM FEC at 30 °C and 500 r/min for 9 d. A voltage of 500 mV was applied; the resulting current per electrode surface (a) lay around 150 µA/cm² after recovery from a strong peak to 550 µA/cm² at inoculation, till it reduced after 80 h of cultivation. The reactors were inoculated at an OD₆₀₀ (b) of 1.75. An abiotic control is shown for the current density and optical density as a black graph (n = 1), the blue graphs show the inoculated experiments (n = 3).