Fig. 4.

Autotrophic growth of C. necator gene deletion strains under ambient CO₂. (A) Growth experiments were conducted in 700-mL bioreactor cultures on minimal medium (JMM) with a continuous sparging of gas (6.25 L/min) with ambient air + 4% hydrogen; control experiments were conducted at 10% CO₂ + 4% hydrogen (supplemented with air). Doubling times (hours) and SDs are shown in parentheses; NG corresponds to no growth. Growth experiments on ambient CO₂ were performed in biological duplicates and showed identical growth curves (±5%); hence, representative curves of a single experiment are shown. We performed control growth experiments on high CO₂ for two strains only once and only up to 50 h to limit extremely high CO₂ turnover in the (nonrecycling) bioreactor setup. (B) Phosphoglycolate salvage in C. necator proceeds mainly via glycolate dehydrogenase and the glycerate pathway to regenerate 3PG for the Calvin cycle. (C) In the absence of the glycerate pathway, glyoxylate is decarboxylated by the malate cycle to CO₂ and NADH, which can be reassimilated by the Calvin cycle. ΔC2, C₂ cycle knockout (ΔgcvTHP); ΔGDH, glycolate dehydrogenase knockout (ΔglcD-kch-glcE-glcF); ΔGP, glycerate pathway knockout (Δgcl-hyi-tsr); ΔMC, malate cycle knockout (ΔaceB); ΔOX, oxalate decarboxylation knockout (Δfrc-oxc); WT, wild type.