Heterotrophic bacteria hydrolyze high molecular weight (HMW) organic matter extracellularly prior to uptake, resulting in diffusive loss of hydrolysis products. An alternative ‘selfish’ uptake mechanism that minimises this loss has recently been found to be common in the ocean. We investigated how HMW organic matter addition affects these two processing mechanisms in surface and bottom waters at three stations in the North Atlantic Ocean. A pulse of HMW organic matter increased cell numbers, as well as the rate and spectrum of extracellular enzymatic activities at both depths. The effects on selfish uptake were more differentiated: in Gulf Stream surface waters and productive surface waters south of Newfoundland, selfish uptake of structurally simple polysaccharides increased upon HMW organic matter addition. The number of selfish bacteria taking up structurally complex polysaccharides, however, was largely unchanged. In contrast, in the oligotrophic North Atlantic gyre, despite high external hydrolysis rates, the number of selfish bacteria was unchanged, irrespective of polysaccharide structure. In deep bottom waters (> 4000 m), structurally complex substrates were processed only by selfish bacteria. Mechanisms of substrate processing—and the extent to which hydrolysis products are released to the external environment—depend on substrate structural complexity and the resident bacterial community.

中文翻译：

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高分子量有机物的脉冲输入改变了海洋细菌群落的底物利用机制

异养细菌在吸收之前会在细胞外水解高分子量 (HMW) 有机物，导致水解产物扩散损失。最近发现，另一种“自私”吸收机制可以最大限度地减少这种损失，这在海洋中很常见。我们研究了 HMW 有机物的添加如何影响北大西洋三个站的表层水和底层水的这两种处理机制。高分子量有机物脉冲增加了细胞数量，以及两个深度的细胞外酶活性的速率和谱。对自私吸收的影响更加不同：在墨西哥湾流地表水域和纽芬兰以南的生产性地表水域中，结构简单多糖的自私吸收随着高分子量有机物的添加而增加。然而，摄取结构复杂的多糖的自私细菌的数量基本上没有变化。相比之下，在贫营养的北大西洋环流中，尽管外部水解率很高，但自私细菌的数量却没有变化，与多糖结构无关。在深海底水域（> 4000 m），结构复杂的基质只能由自私的细菌处理。底物处理机制以及水解产物释放到外部环境的程度取决于底物结构的复杂性和常驻细菌群落。