TABLE 2 

Conversion of substrates to biomass, CO2, organic acids, and H2 by R. palustris during exponential growtha

SubstrateDoubling time (h)Yield (mol/mol organic C consumed)b% C recoverye% electron recoverye
BiomasscCO2Organic acidsdH2
WTNifA*WTNifA*WTNifA*WTNifA*WTNifA*WTNifA*WTNifA*
Fumarate10.6 ± 1.0f13.2 ± 0.8f62 ± 347 ± 228 ± 129 ± 112 ± 230 ± 318 ± 3g101 ± 5106 ± 2104 ± 6109 ± 3
Succinate6.5 ± 0.48.2 ± 0.582 ± 367 ± 315 ± 127 ± 10.1 ± 0.00.1 ± 0.023 ± 197 ± 494 ± 3106 ± 499 ± 3
Acetateh8.4 ± 0.69.4 ± 0.688 ± 879 ± 46 ± 117 ± 20021 ± 393 ± 896 ± 598 ± 999 ± 5
Butyrate-HCO38.6 ± 0.410.7 ± 1.083 ± 684 ± 6−18 ± 4−11 ± 328 ± 323 ± 511 ± 394 ± 597 ± 597 ± 599 ± 8
ButyrateNo growth32.4 ± 7.667 ± 126 ± 124 ± 241 ± 1097 ± 1496 ± 15
  • a Unlabeled cultures were grown in minimal medium with NH4+ as the nitrogen source. Values are averages from 3 to 5 biological replicates ± SD based on samples taken during early exponential growth.

  • b  Values are normalized for organic C consumed to account for acetate having two carbon atoms, whereas the other substrates have four. Negative signs indicate that there was a net consumption of CO2, which was made possible by the NaHCO3 supplement.

  • c  Moles of biomass were determined from the R. palustris 42OL elemental composition (25): CH1.8N0.18O0.38 (mole weight, 22.426 g/mol).

  • d Malate was excreted during growth on fumarate, fumarate was excreted during growth on succinate, and acetate was excreted during growth on butyrate.

  • e  The percentage of organic carbon and electrons consumed that were observed in products. The sum of the values in biomass, CO2, and organic acids would equal 100 for full carbon recovery. Electron recovery was based on available hydrogen as described previously (7, 26).

  • f  Growth rates during the second growth phase on fumarate.

  • g  Calculated by grouping fumarate and malate as a single metabolite [i.e., dH2/d(fumarate + malate) × 100/4 carbon atoms]. The H2 yield from fumarate consumed alone would give a value of 12 ± 2.

  • h  The acetate data were previously published (7).