Conrad R, Klose M
Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, D-35043, Marburg, Germany
FEMS Microbiol Ecol. 1999 Oct 1;30(2):147-155. doi: 10.1111/j.1574-6941.1999.tb00643.x.
Washed excised roots of rice (Oryza sativa) produced H(2), CH(4), acetate, propionate and butyrate when incubated under anoxic conditions. Acetate production was most pronounced with a maximum rate (mean+/-standard error; four different root preparations) of 3.4+/-0.6 µmol h(-1) g-dry weight(-1) roots, compared to 0.45+/-0.13, 0.06+/-0.03, and 0.04+/-0.01 µmol h(-1) g-dw(-1) for propionate, butyrate and CH(4)1 kPa after one day of incubation. Then it decreased and reached more or less constant concentrations of about 50-80 Pa after about 7-8 days. Hydrogen partial pressures were always high enough to allow exergonic methanogenesis (DeltaG=-67 to -98 kJ mol(-1) CH(4)) and exergonic homoacetogenesis (DeltaG=-18 to -48 kJ mol(-1) acetate) from H(2) plus CO(2). Radioactive bicarbonate/CO(2) was incorporated into CH(4), acetate and propionate. The specific radioactivities of the products indicated that CH(4) was exclusively produced from H(2)/CO(2) confirming a previous study. The contribution of CO(2) to the production of acetate and propionate was 32-39% and 42-61%, respectively, assuming that each carbon atom was equally labeled. Propionate also became radioactively labeled, when the roots were incubated with either [1-(14)C]acetate or [2-(14)C]acetate accounting for 60-76% of total propionate production. Reductive formation of propionate was thermodynamically favorable both from H(2) plus acetate plus CO(2) (DeltaG=-15 to -38 kJ mol(-1) propionate) and from H(2) plus CO(2) (DeltaG=-34 to -85 kJ mol(-1) propionate). A substantial fraction of propionate was apparently reductively formed from acetate and/or CO(2). In conclusion, our results demonstrate an intensive anaerobic dark metabolism of CO(2) on washed rice roots with reduction of CO(2) contributing significantly to the production of acetate, propionate and CH(4). The CO(2) reduction seemed to be driven by decay and fermentation of root material.
将水稻（Oryza sativa）切除的根系洗净后，在缺氧条件下培养时会产生氢气、甲烷、乙酸盐、丙酸盐和丁酸盐。乙酸盐的产生最为显著，最大速率（平均值±标准误差；四种不同的根系制剂）为3.4±0.6 μmol h⁻¹ g干重⁻¹根系，相比之下，培养一天后，丙酸盐、丁酸盐和甲烷的速率分别为0.45±0.13、0.06±0.03和0.04±0.01 μmol h⁻¹ g干重⁻¹。然后其下降，在大约7 - 8天后达到或多或少恒定的浓度，约为50 - 80 Pa。氢气分压始终足够高，能够使氢气与二氧化碳发生放能产甲烷作用（ΔG = -67至-98 kJ mol⁻¹甲烷）和放能同型产乙酸作用（ΔG = -18至-48 kJ mol⁻¹乙酸盐）。放射性碳酸氢盐/二氧化碳被整合到甲烷、乙酸盐和丙酸盐中。产物的比放射性表明，甲烷完全由氢气/二氧化碳产生，这证实了先前的一项研究。假设每个碳原子被同等标记，二氧化碳对乙酸盐和丙酸盐产生的贡献分别为32 - 39%和42 - 61%。当根系与[1-(¹⁴)C]乙酸盐或[2-(¹⁴)C]乙酸盐一起培养时，丙酸盐也会被放射性标记，占丙酸盐总产量的60 - 76%。从氢气加乙酸盐加二氧化碳（ΔG = -15至-38 kJ mol⁻¹丙酸盐）以及从氢气加二氧化碳（ΔG = -34至-85 kJ mol⁻¹丙酸盐）还原形成丙酸盐在热力学上都是有利的。相当一部分丙酸盐显然是由乙酸盐和/或二氧化碳还原形成的。总之，我们的结果表明，洗净的水稻根系存在强烈的厌氧暗代谢二氧化碳过程，二氧化碳的还原对乙酸盐、丙酸盐和甲烷的产生有显著贡献。二氧化碳的还原似乎是由根系物质的腐烂和发酵驱动的。
