The cyanobacteria Prochlorococcus and Synechococcus are responsible for around 10% of global net primary productivity, serving as part of the foundation of marine food webs. Heterotrophic bacteria are often co-isolated with these picocyanobacteria in seawater enrichment cultures that contain no added organic carbon; heterotrophs grow on organic carbon supplied by the photolithoautotrophs. For examining the selective pressures shaping autotroph/heterotroph interactions, we have made use of unialgal enrichment cultures of Prochlorococcus and Synechococcus maintained for hundreds to thousands of generations in the lab. We examine the diversity of heterotrophs in 74 enrichment cultures of these picocyanobacteria obtained from diverse areas of the global oceans. Heterotroph community composition differed between clades and ecotypes of the autotrophic ‘hosts’ but there was significant overlap in heterotroph community composition across these cultures. Collectively, the cultures were comprised of many shared taxa, even at the genus level. Yet, observed differences in community composition were associated with time since isolation, location, depth, and methods of isolation. The majority of heterotrophs in the cultures are rare in the global ocean, but enrichment conditions favor the opportunistic outgrowth of these rare bacteria. However, we found a few examples, such as bacteria in the family Rhodobacteraceae, of heterotrophs that were ubiquitous and abundant in cultures and in the global oceans. We found their abundance in the wild is also positively correlated with that of picocyanobacteria. Particular conditions surrounding isolation have a persistent effect on long-term culture composition, likely from bottlenecking and selection that happen during the early stages of enrichment for the picocyanobacteria. We highlight the potential for examining ecologically relevant relationships by identifying patterns of distribution of culture-enriched organisms in the global oceans.

中文翻译：

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海洋微蓝细菌培养物中共生异养菌的微生物多样性

蓝细菌Prochlorococcus和Synechococcuscus约占全球净初级生产力的10％，是海洋食物网基础的一部分。在不添加有机碳的海水富集培养中，异养细菌通常与这些微蓝细菌共分离。异养生物在由光刻自养生物提供的有机碳上生长。为了检查影响自养/异养相互作用的选择性压力，我们利用了原百球藻和原球菌的单倍体富集培养物在实验室中维持了数百至数千代。我们研究了从全球海洋不同地区获得的这些微蓝细菌的74种富集培养物中的异养生物的多样性。进化枝和生态型的自养“宿主”的异养族群落组成有所不同，但这些文化的异养族群落组成存在明显的重叠。总体而言，文化由许多共享的分类单元组成，即使在属级别也是如此。然而，自隔离，地点，深度和隔离方法以来，观察到的社区组成差异与时间相关。养殖中的大多数异养菌在全球海洋中都很罕见，但是富集条件有利于这些稀有细菌的机会性繁殖。但是，我们发现了一些例子，例如，红细菌科中的细菌，异养菌在文化和全球海洋中都普遍存在且丰富。我们发现它们在野外的丰度也与picocyanobacteria的丰度成正相关。围绕隔离的特殊条件可能对长期培养物成分产生持久影响，这可能是由于在蓝藻细菌富集的早期阶段出现的瓶颈和选择。我们通过确定全球海洋中富含文化的生物的分布方式，强调了检查与生态相关的关系的潜力。