Figure 1.

Mass and electron balance batch tests, along with isotope labelling experiments, confirmed that anaerobic ethane/butane oxidation was coupled to nitrate reduction by the bioreactor enrichment cultures fed with C₂H₆/C₄H₁₀; (A, B) typical biochemical profiles of the ethane (A, started on Day 490) and butane (B, started on Day 1100) systems showing simultaneous nitrate and ethane/butane consumption with transitory formation of nitrite, and production of dinitrogen gas and ammonium; there were two distinct phases for NO₃⁻ reduction; in Phase 1, NO₃⁻ was reduced to NO₂⁻ and N₂, with negligible NH₄⁺ production, while in Phase 2, the accumulated NO₂⁻ was reduced to both N₂ and NH₄⁺; (C, D) average nitrogen- and electron balances calculated from the three batch tests for C₂H₆- (C) and C₄H₁₀- (D) fed bioreactors (Supplementary Table 1 shows the complete data and calculation); error bars represent standard errors from biological triplicates; oxidation of ¹³C₂H₆ (E) or ¹³C₄H₁₀ (F) to ¹³CO₂, and reduction of ¹⁵NO₃⁻ to ¹⁵NH₄⁺ and ²⁹N₂ with temporary generation of ¹⁵NO₂⁻ during the isotope labelling test.