Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA.
mBio. 2022 Feb 22;13(1):e0257121. doi: 10.1128/mbio.02571-21. Epub 2022 Jan 11.
The marine cyanobacterium numerically dominates the phytoplankton community of the nutrient-limited open ocean, establishing itself as the most abundant photosynthetic organism on Earth. This ecological success has been attributed to lower cell quotas for limiting nutrients, superior resource acquisition, and other advantages associated with cell size reduction and genome streamlining. In this study, we tested the prediction that outcompetes its rivals for scarce nutrients and that this advantage leads to its numerical success in nutrient-limited waters. Strains of and its sister genus grew well in both mono- and cocultures when nutrients were replete. However, in nitrogen-limited medium, outgrew but only when heterotrophic bacteria were also present. In the nitrogen-limited medium, the heterotroph Alteromonas macleodii outcompeted for nitrogen but only if stimulated by the exudate released by or if a proxy organic carbon source was provided. Genetic analysis of suggested that it outcompetes for nitrate and/or nitrite, during which cocultured grows on ammonia or other available nitrogen species. We propose that can stimulate antagonism between heterotrophic bacteria and potential phytoplankton competitors through a metabolic cross-feeding interaction, and this stimulation could contribute to the numerical success of in nutrient-limited regions of the ocean. In nutrient-poor habitats, competition for limited resources is thought to select for organisms with an enhanced ability to scavenge nutrients and utilize them efficiently. Such adaptations characterize the cyanobacterium , the most abundant photosynthetic organism in the nutrient-limited open ocean. In this study, the competitive superiority of over a rival cyanobacterium, , was captured in laboratory culture. Critically, this outcome was achieved only when key aspects of the open ocean were simulated: a limited supply of nitrogen and the presence of heterotrophic bacteria. The results indicate that promotes its numerical dominance over by energizing the heterotroph's ability to outcompete for available nitrogen. This study demonstrates how interactions between trophic groups can influence interactions within trophic groups and how these interactions likely contribute to the success of the most abundant photosynthetic microorganism.
海洋蓝藻在营养受限的开阔海域中在数量上占据主导地位，成为地球上最丰富的光合生物。这种生态上的成功归因于对限制营养物质的细胞配额较低，优越的资源获取能力以及与细胞尺寸缩小和基因组简化相关的其他优势。在这项研究中，我们检验了这样一种预测，即在稀缺营养物质方面胜过其竞争对手，并且这种优势导致其在营养受限水域中占据数量优势。当营养物质充足时， 和它的姐妹属 的菌株在单培养和共培养中都能很好地生长。然而，在氮限制培养基中， 只有在异养细菌存在的情况下才能超过 。在氮限制培养基中，异养菌 能够与 竞争氮，但前提是受到 释放的分泌物刺激，或者提供一种替代有机碳源。 的遗传分析表明，在共培养过程中， 可以通过代谢交叉喂养相互作用来竞争硝酸盐和/或亚硝酸盐，在此期间，共培养的 可以利用氨或其他可用氮物种生长。我们提出， 可以通过代谢交叉喂养相互作用刺激异养细菌与潜在的浮游植物竞争者之间的拮抗作用，这种刺激可能有助于 在海洋营养受限区域的数量成功。 在营养贫乏的栖息地中，对有限资源的竞争被认为会选择那些具有增强的营养物质吸收能力和有效利用能力的生物。这种适应特征体现在海洋中数量最丰富的光合生物——蓝藻中。在这项研究中，在实验室培养中捕获了竞争对手蓝藻的竞争优势。至关重要的是，只有在模拟了开阔海洋的几个关键方面时，才会出现这种结果：氮的供应有限和异养细菌的存在。结果表明， 通过增强异养细菌竞争可用氮的能力，促进了其在数量上对 的优势。这项研究表明，营养群体之间的相互作用如何影响营养群体内部的相互作用，以及这些相互作用如何有助于最丰富的光合微生物的成功。
