Microbial mats: A joint venture
Microbial mats: A joint venture
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微生物垫：合资企业
DOI：
10.1016/0025-3227(93)90146-m
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发表时间：
1993
期刊：
影响因子：
2.9
通讯作者：
H. Gemerden
中科院分区：
文献类型：
--
作者：
H. Gemerden
微生物席的特征是由几个功能群的微生物占主导地位：蓝藻，无色硫细菌，紫色硫细菌和硫酸盐还原菌。它们共同的代谢活动导致了陡峭的环境微梯度，特别是氧气和硫化物。大多数微生物垫的驱动力是蓝藻和藻类的光合作用。随后，硫酸盐还原菌利用蓝藻的排泄、溶解和分解产物，通过硫酸盐的异化还原产生硫化物。无色硫细菌是一种化能营养生物，主要利用氧气氧化硫化物和其他还原形式的硫来获得能量。还原的硫物质的氧化还提供用于将二氧化碳还原成细胞碳的还原当量。硫化物氧化的最终产物是硫酸盐，其中元素硫作为主要中间产物沉积在细胞外。紫硫细菌主要是厌氧光养生物，只利用硫化物和其他还原形式的硫作为电子供体，将CO2还原为细胞碳。通常，硫暂时储存在细胞内。还原态硫氧化的最终产物是硫酸盐。在氧气和硫化物浓度梯度陡峭、通常不重叠的生态系统中，这些代谢不同的微生物类群的生态位似乎在空间上是分离的。然而，无色硫细菌和紫色硫细菌的最大活菌数都发现在顶部5-10 mm的垫。出乎意料的是，硫酸盐还原菌的活菌数也在同一深度层位达到峰值。硫化物对大多数产氧光养生物有抑制作用。直接在蓝细菌层下面产生的硫化物可能会抑制它们的生长，从而抑制整个生态系统的生长。在微生物垫中，无色和紫色硫细菌的联合作用使这种影响最小化。无色硫细菌通常比紫色硫细菌对硫化物具有更高的亲和力，然而，在微生物垫中，它们的活性受到低供氧速率的阻碍。无色硫细菌的纯培养研究表明，当氧气供应不足时，硫化物被不完全氧化，导致紫色硫细菌产生潜在的电子供体，如硫，硫代硫酸盐和多硫化物。在没有紫色硫细菌的情况下，无色硫细菌将由于缺氧而不能维持低硫化物浓度，这反过来又会导致对产氧光合作用的抑制增加。因此，上述所有四组功能微生物的联合作用有效地导致了这些最近的“基质”的最佳生长。
Microbial mats characteristically are dominated by a few functional groups of microbes: cyanobacteria, colorless sulfur bacteria, purple sulfur bacteria, and sulfate-reducing bacteria. Their combined metabolic activities result in steep environmental microgradients, particularly of oxygen and sulfide.The driving force of most microbial mats is photosynthesis by cyanobacteria and algae. Subsequently, sulfate-reducing bacteria, using excretion-, lysis-, and decomposition products of cyanobacteria, produce sulfide by the dissimilatory reduction of sulfate. The sulfide can be reoxidized to sulfate by colorless and purple sulfur bacteria.Colorless sulfur bacteria are chemotrophic organisms primarily oxidizing sulfide and other reduced forms of sulfur with oxygen to obtain energy. The oxidation of reduced sulfur species also provides reducing equivalents for the reduction of carbon dioxide to cellular carbon. The final product of sulfide oxidation is sulfate, with elemental sulfur, deposited extracellularly, as the principal intermediate.Purple sulfur bacteria primarily are anaerobic phototrophic organisms using sulfide and other reduced forms of sulfur exclusively as the electron donor for the reduction of CO2to cellular carbon. Usually, sulfur is temporarily stored intracellularly. The final product of the oxidation of reduced forms of sulfur is sulfate.The niches for these metabolically different groups of microbes in ecosystems with steep, often non-overlapping, gradients of oxygen and sulfide appear to be spatially separated. However, maximum viable counts of colorless sulfur bacteria and purple sulfur bacteria were both found in the top 5–10 mm of mats. Unexpectedly, viable counts of sulfate-reducing bacteria also peaked at the same depth horizon.Sulfide is inhibitory for most oxygenic phototrophs. Sulfide production immediately underneath the layer of cyanobacteria might inhibit their growth, and, consequently, that of the entire ecosystem. In microbial mats this effect is minimized by the combined action of colorless and purple sulfur bacteria. Colorless sulfur bacteria generally have a much higher affinity for sulfide than purple sulfur bacteria, however, in microbial mats, their activity is hampered by low oxygen supply rates. As shown by pure culture studies with colorless sulfur bacteria, sulfide is incompletely oxidized when oxygen is short in supply, resulting in the production of potential electron donors for purple sulfur bacteria, such as sulfur, thiosulfate and polysulfides. In the absence of purple sulfur bacteria, colorless sulfur bacteria would not be able to maintain a low sulfide concentration due to shortage of oxygen, which in turn would result in increased inhibition of oxygenic photosynthesis.It thus appears that the combined action of all four groups of functional microbes mentioned effectively results in optimal growth of these recent “stromatolites”.