Deep-sea sediments are populated by diverse microbial communities that derive their nutritional requirements from the degradation of organic matter. Extracellular hydrolytic enzymes play a key role in the survival of microbes by enabling them to access and degrade complex organic compounds that are found in seafloor sediments. Despite their importance, extracellular enzymatic activity is poorly characterized at water depths greater than a few hundred meters where physical properties, such as pressure and temperature, create a unique environment for influencing enzyme behavior. Here, we investigated microbial communities and enzyme activities in surface sediment collected at four sampling stations in the central Mediterranean Sea at water depths ranging from 800 to 2200 m. Fluorometric assays revealed that extracellular hydrolytic activity varied according to substrate type and water depth which suggests that the distributions of these enzymes within this basin are not homogenous. Furthermore, enzyme activities indicated substantial demand for phosphomonoesters and proteins, with measurable but much lower demand for polysaccharides. Barcoded amplicon sequencing of bacterial and archaeal SSU genes revealed that microbial communities varied across sampling stations and some groups displayed water-depth related trends. Our results demonstrate that heterotrophic capabilities of microbes in deep-sea Mediterranean sediments can differ substantially even within the same region.

深海沉积物由各种微生物群落组成，这些微生物群落的营养需求来自有机物的降解。细胞外水解酶通过使微生物能够接触和降解海底沉积物中发现的复杂有机化合物，在微生物的生存中发挥关键作用。尽管它们具有重要意义，但在大于几百米的水深处，细胞外酶的活性却很差，因为那里的物理特性（如压力和温度）会产生影响酶行为的独特环境。在这里，我们调查了地中海中部四个采样站在800至2200 m的水深处收集的表面沉积物中的微生物群落和酶活性。荧光测定表明，胞外水解活性根据底物类型和水深而变化，这表明这些酶在该盆地内的分布不均匀。此外，酶活性表明对磷酸单酯和蛋白质的大量需求，而对多糖的需求却可测量但低得多。细菌和古细菌SSU基因的条形码扩增子测序表明，微生物群落在各个采样站之间各不相同，并且某些群体显示出与水深有关的趋势。我们的结果表明，即使在同一地区，地中海深海沉积物中微生物的异养能力也可能存在很大差异。酶的活性表明对磷酸单酯和蛋白质的大量需求，而对多糖的需求却可测量但低得多。细菌和古细菌SSU基因的条形码扩增子测序表明，微生物群落在各个采样站之间各不相同，并且某些群体显示出与水深有关的趋势。我们的结果表明，即使在同一地区，地中海深海沉积物中微生物的异养能力也可能存在很大差异。酶的活性表明对磷酸单酯和蛋白质的大量需求，而对多糖的需求却可测量但低得多。细菌和古细菌SSU基因的条形码扩增子测序表明，微生物群落在各个采样站之间各不相同，并且某些群体显示出与水深有关的趋势。我们的结果表明，即使在同一地区，地中海深海沉积物中微生物的异养能力也可能存在很大差异。