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首页> 美国卫生研究院文献>Applied and Environmental Microbiology >Functional Exoenzymes as Indicators of Metabolically Active Bacteria in 124000-Year-Old Sapropel Layers of the Eastern Mediterranean Sea
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Functional Exoenzymes as Indicators of Metabolically Active Bacteria in 124000-Year-Old Sapropel Layers of the Eastern Mediterranean Sea

机译：功能性外酶作为东地中海124000年历史腐烂层中代谢活性细菌的指标

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摘要

Hydrolytic exoenzymes as indicators of metabolically active bacteria were investigated in four consecutive sapropel layers collected from bathyal sediments of the eastern Mediterranean Sea. For comparison, the organic carbon-poor layers between the sapropels, sediment from the anoxic Urania basin, and sediments of intertidal mud flats of the German Wadden Sea were also analyzed. The sapropel layers contained up to 1.5 · 108 bacterial cells cm−3, whereas cell numbers in the intermediate layers were lower by a factor of 10. In sapropels, the determination of exoenzyme activity with fluorescently labeled substrate analogues was impaired by the strong adsorption of up to 97% of the enzymatically liberated fluorophores (4-methylumbelliferone [MUF] and 7-amino-4-methylcoumarin [MCA]) to the sediment particles. Because all established methods for the extraction of adsorbed fluorophores proved to be inadequate for sapropel sediments, we introduce a correction method which is based on the measurement of equilibrium adsorption isotherms for both compounds. Using this new approach, high activities of aminopeptidase and alkaline phosphatase were detected even in a 124,000-year-old sapropel layer, whereas the activity of β-glucosidase was low in all layers. So far, it had been assumed that the organic matter which constitutes the sapropels is highly refractory. The high potential activities of bacterial exoenzymes indicate that bacteria in Mediterranean sapropels are metabolically active and utilize part of the subfossil kerogen. Since a high adsorption capacity was determined not only for the low-molecular-weight compounds MUF and MCA but also for DNA, the extraordinarily strong adsorption of structurally different substrates to the sapropel matrix appears to be the major reason for the long-term preservation of biodegradable carbon in this environment.
机译：水解外切酶作为代谢活性细菌的指标，在​​地中海东部海相沉积物中收集的四个连续腐腐层中进行了研究。为了进行比较，还分析了腐殖质，缺氧性Urania盆地的沉积物和德国瓦登海潮间带滩涂沉积物之间的有机碳贫乏层。腐殖质层最多包含1.5·10 8 细菌细胞cm -3 ，而中间层中的细胞数降低了10倍。多达97％的酶促释放的荧光团（4-甲基伞形酮[MUF]和7-氨基-4-甲基香豆素[MCA]）强烈吸附到沉淀物颗粒上，从而削弱了荧光标记底物类似物的外切酶活性。由于所有确定的提取吸附的荧光团的方法都证明不足以用于腐殖质沉积物，因此我们引入了一种校正方法，该方法基于两种化合物的平衡吸附等温线的测量。使用这种新方法，即使在具有124,000年历史的腐烂层中也检测到了高活性的氨肽酶和碱性磷酸酶，而在所有层中β-葡萄糖苷酶的活性均较低。迄今为止，已经假定构成腐殖质的有机物是高度难熔的。细菌外切酶的高潜在活性表明，地中海腐腐菌中的细菌具有代谢活性，并利用部分化石干酪根。由于不仅对低分子量化合物MUF和MCA以及对DNA都具有很高的吸附能力，所以结构上不同的底物对腐殖质基质的异常强吸附似乎是长期保存苯丙胺的主要原因。在这种环境下可生物降解的碳。

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