Jonkers H M, Koh I-O, Behrend P, Muyzer G, de Beer D
Max Planck Institute for Marine Microbiology, D-28359, Bremen, Germany.
Microb Ecol. 2005 Feb;49(2):291-300. doi: 10.1007/s00248-004-0260-y. Epub 2005 Jun 17.
The sulfate-reducing bacterium strain SRB D2 isolated from the photic zone of a hypersaline microbial mat, from Lake Chiprana, NE Spain, respired pyruvate, alanine, and alpha-ketoglutarate but not formate, lactate, malate, succinate, and serine at significant rates under fully oxic conditions. Dehydrogenase enzymes of only the former substrates are likely oxygen-tolerant as all substrates supported anaerobic sulfate reduction. No indications were found, however, that aerobic respiration supported growth. Although strain SRB D2 appeared phylogenetically closely related to the oxygen-tolerant sulfate-reducing bacterium Desulfovibrio oxyclinae, substrate spectra were markedly different. Most-probable-number (MPN) estimates of sulfate-reducing bacteria and aerobic heterotrophic bacteria indicated that the latter were numerically dominant in both the photic and aphotic zones of the mat. Moreover, substrate spectra of representative isolates showed that the aerobic heterotrophic bacteria are metabolically more diverse. These findings indicate that sulfate-reducing bacteria in the fully oxic photic zone of mats have to compete with aerobic heterotrophic bacteria for organic substrates. Porewater analysis revealed that total carbohydrates and low-molecular-weight carbon compounds (LMWC) made up substantial fractions of the total dissolved organic carbon (DOC) pool and that nighttime degradation of the former was concomitant with increased concentration of the latter. Our findings indicate that aerobic respiration by sulfate-reducing bacteria contributes to organic carbon mineralization in the oxic zone of microbial mats as daytime porewater LMWC concentrations are above typical half-saturation constants.
从西班牙东北部奇普拉纳湖高盐度微生物垫的光合区分离出的硫酸盐还原菌株SRB D2，在完全有氧条件下，能够以显著速率利用丙酮酸、丙氨酸和α-酮戊二酸进行呼吸，但不能利用甲酸、乳酸、苹果酸、琥珀酸和丝氨酸。只有前几种底物的脱氢酶可能耐受氧气，因为所有这些底物都能支持厌氧硫酸盐还原。然而，没有迹象表明有氧呼吸能支持其生长。尽管菌株SRB D2在系统发育上似乎与耐氧硫酸盐还原菌嗜氧脱硫弧菌密切相关，但其底物谱却明显不同。对硫酸盐还原菌和好氧异养菌的最大可能数（MPN）估计表明，后者在微生物垫的光合区和无光区在数量上占主导地位。此外，代表性分离株的底物谱表明，好氧异养菌的代谢更为多样。这些发现表明，微生物垫完全有氧光合区中的硫酸盐还原菌必须与好氧异养菌竞争有机底物。孔隙水分析表明，总碳水化合物和低分子量碳化合物（LMWC）在总溶解有机碳（DOC）池中占很大比例，并且前者的夜间降解伴随着后者浓度的增加。我们的研究结果表明，由于白天孔隙水LMWC浓度高于典型的半饱和常数，硫酸盐还原菌的有氧呼吸有助于微生物垫有氧区的有机碳矿化。
