Cruz Bianca N, Neuer Susanne
School of Life Sciences, Arizona State University, Tempe, AZ, United States.
Center for Fundamental and Applied Microbiomics, Biodesign Institute, Arizona State University, Tempe, AZ, United States.
Front Microbiol. 2019 Aug 13;10:1864. doi: 10.3389/fmicb.2019.01864. eCollection 2019.
Marine picocyanobacteria are ubiquitous primary producers across the world's oceans, and play a key role in the global carbon cycle. Recent evidence stemming from investigations have shown that picocyanobacteria are able to sink out of the euphotic zone to depth, which has traditionally been associated with larger, mineral ballasted cells. The mechanisms behind the sinking of picocyanobacteria remain a point of contention, given that they are too small to sink on their own. To gain a mechanistic understanding of the potential role of picocyanobacteria in carbon export, we tested their ability to form "suspended" (5-60 μm) and "visible" (ca. > 0.1 mm) aggregates, as well as their production of transparent exopolymer particles (TEP)-which are a key component in the formation of marine aggregates. Additionally, we investigated if interactions with heterotrophic bacteria play a role in TEP production and aggregation in and by comparing xenic and axenic cultures. We observed TEP production and aggregation in batch cultures of axenic , but not in axenic . Heterotrophic bacteria enhanced TEP production as well as suspended and visible aggregate formation in , while in , aggregation was enhanced with no changes in TEP. Aggregation experiments using a natural plankton community dominated by picocyanobacteria resulted in aggregation only in the presence of the ballasting mineral kaolinite, and only when were in their highest seasonal abundance. Our results point to a different export potential between the two picocyanobacteria, which may be mediated by interactions with heterotrophic bacteria and presence of ballasting minerals. Further studies are needed to clarify the mechanistic role of bacteria in TEP production and aggregation of these picocyanobacteria.
海洋聚球蓝细菌是遍布全球海洋的初级生产者，在全球碳循环中发挥着关键作用。最近的调查证据表明，聚球蓝细菌能够从真光层下沉到深层，而传统上这与更大的、有矿物质作为载体的细胞有关。聚球蓝细菌下沉背后的机制仍然存在争议，因为它们太小，无法自行下沉。为了从机制上理解聚球蓝细菌在碳输出中的潜在作用，我们测试了它们形成“悬浮”（5 - 60微米）和“可见”（约> 0.1毫米）聚集体的能力，以及它们产生透明胞外聚合物颗粒（TEP）的能力——TEP是海洋聚集体形成的关键成分。此外，我们通过比较含菌和无菌培养物，研究了与异养细菌的相互作用是否在TEP产生和聚集体形成中发挥作用。我们观察到无菌的聚球蓝细菌分批培养物中有TEP产生和聚集体形成，但无菌的聚球蓝细菌中没有。异养细菌增强了聚球蓝细菌中TEP的产生以及悬浮和可见聚集体的形成，而在聚球蓝细菌中，聚集体形成增强，TEP没有变化。使用以聚球蓝细菌为主的天然浮游生物群落进行的聚集体实验表明，只有在有作为载体的矿物高岭石存在时，并且只有当聚球蓝细菌处于其最高季节丰度时才会发生聚集体形成。我们的结果表明，这两种聚球蓝细菌之间存在不同的输出潜力，这可能是由与异养细菌的相互作用和作为载体的矿物质的存在介导的。需要进一步研究来阐明细菌在这些聚球蓝细菌的TEP产生和聚集体形成中的机制作用。
