Moran James J, House Christopher H, Freeman Katherine H, Ferry James G
Department of Geosciences and Penn State Astrobiology Research Center, Penn State University, 220 Deike Bldg., University Park, PA 16802, USA.
Archaea. 2005 May;1(5):303-9. doi: 10.1155/2005/650670.
We used (13)C-labeled methane to document the extent of trace methane oxidation by Archaeoglobus fulgidus, Archaeoglobus lithotrophicus, Archaeoglobus profundus, Methanobacterium thermoautotrophicum, Methanosarcina barkeri and Methanosarcina acetivorans. The results indicate trace methane oxidation during growth varied among different species and among methanogen cultures grown on different substrates. The extent of trace methane oxidation by Mb. thermoautotrophicum (0.05 +/- 0.04%, +/- 2 standard deviations of the methane produced during growth) was less than that by M. barkeri (0.15 +/- 0.04%), grown under similar conditions with H(2) and CO(2). Methanosarcina acetivorans oxidized more methane during growth on trimethylamine (0.36 +/- 0.05%) than during growth on methanol (0.07 +/- 0.03%). This may indicate that, in M. acetivorans, either a methyltransferase related to growth on trimethylamine plays a role in methane oxidation, or that methanol is an intermediate of methane oxidation. Addition of possible electron acceptors (O(2), NO(3) (-), SO(4) (2-), SO(3) (2-)) or H(2) to the headspace did not substantially enhance or diminish methane oxidation in M. acetivorans cultures. Separate growth experiments with FAD and NAD(+) showed that inclusion of these electron carriers also did not enhance methane oxidation. Our results suggest trace methane oxidized during methanogenesis cannot be coupled to the reduction of these electron acceptors in pure cultures, and that the mechanism by which methane is oxidized in methanogens is independent of H(2) concentration. In contrast to the methanogens, species of the sulfate-reducing genus Archaeoglobus did not significantly oxidize methane during growth (oxidizing 0.003 +/- 0.01% of the methane provided to A. fulgidus, 0.002 +/- 0.009% to A. lithotrophicus and 0.003 +/- 0.02% to A. profundus). Lack of observable methane oxidation in the three Archaeoglobus species examined may indicate that methyl-coenzyme M reductase, which is not present in this genus, is required for the anaerobic oxidation of methane, consistent with the "reverse methanogenesis" hypothesis.
我们使用¹³C标记的甲烷来记录嗜热栖热古菌、嗜岩栖热古菌、深渊栖热古菌、嗜热自养甲烷杆菌、巴氏甲烷八叠球菌和食乙酰甲烷八叠球菌对微量甲烷的氧化程度。结果表明，生长过程中的微量甲烷氧化在不同物种以及在不同底物上生长的产甲烷菌培养物之间存在差异。嗜热自养甲烷杆菌的微量甲烷氧化程度（0.05±0.04%，±生长过程中产生的甲烷的2个标准差）低于在类似条件下以H₂和CO₂为底物生长的巴氏甲烷八叠球菌（0.15±0.04%）。食乙酰甲烷八叠球菌在三甲胺上生长时氧化的甲烷（0.36±0.05%）比在甲醇上生长时（0.07±0.03%）更多。这可能表明，在食乙酰甲烷八叠球菌中，要么与在三甲胺上生长相关的甲基转移酶在甲烷氧化中起作用，要么甲醇是甲烷氧化的中间体。向顶空添加可能的电子受体（O₂、NO₃⁻、SO₄²⁻、SO₃²⁻）或H₂并没有显著增强或减弱食乙酰甲烷八叠球菌培养物中的甲烷氧化。分别用FAD和NAD⁺进行的生长实验表明，包含这些电子载体也没有增强甲烷氧化。我们的结果表明，在纯培养物中，产甲烷过程中氧化的微量甲烷不能与这些电子受体的还原偶联，并且产甲烷菌中甲烷氧化的机制与H₂浓度无关。与产甲烷菌相反，硫酸盐还原菌属嗜热栖热古菌的物种在生长过程中没有显著氧化甲烷（嗜热栖热古菌氧化提供的甲烷的0.003±0.01%，嗜岩栖热古菌为0.002±0.009%，深渊栖热古菌为0.003±0.02%）。在所检测的三种嗜热栖热古菌物种中未观察到甲烷氧化，这可能表明该属中不存在的甲基辅酶M还原酶是甲烷厌氧氧化所必需的，这与“逆向产甲烷”假说一致。
