Department of Civil and Environmental Engineering Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Environ Microbiol. 2012 Jan;14(1):191-206. doi: 10.1111/j.1462-2920.2011.02598.x. Epub 2011 Oct 9.
Deep-water nutrient injection in the North Pacific Subtropical Gyre provides an aperiodic yet significant source of inorganic nutrients to the nutrient-limiting surface waters, and has been implicated in phytoplankton bloom formation. Here we examined short-term transcriptional responses of surface water picoplankton assemblages in a deep-sea water (DSW) mixing experiment. Both flow cytometric and transcriptomic analysis indicated stimulation of an Alteromonas-like population in the DSW-amended treatment after 12 h, relative to the control. Among the highly expressed alteromonad transcripts in DSW-treated samples, those encoding genes associated with chemotaxis, cell motility and carbon metabolism were most highly represented, relative to the control. Similarly, Prochlorococcus showed significantly higher levels of transcripts associated with carbon fixation and photosynthesis, as well as slightly increased cell density, relative to the control. Although other microbial taxa did not exhibit enhanced growth, DSW-stimulated changes in their genome-wide transcriptional profiles were still readily detectable. Cell-associated cyanophage DNA and cDNA profiles suggested DSW stimulation of phage-mediated cell lysis, in previously infected cells. Comparison of the DSW-responsive Alteromonas populations, to previously reported dissolved organic matter (DOM)-responding alteromonads (McCarren et al., 2010), revealed differential transcript abundances, predominantly among genes encoding mobile elements and phage-related genes. Transcript representation in other metabolic pathways differed significantly between Alteromonas populations in the two different treatments, suggesting perturbation-specific metabolic responses to DSW and DOM. In total, the results provide new insight into short-term responses of picoplankton to DSW mixing, which occur prior to the more well-studied, longer-term growth responses of larger phytoplankton species.
北太平洋亚热带涡旋中的深水营养注入为营养限制的表层水提供了不定期但重要的无机营养源，并与浮游植物爆发的形成有关。在这里，我们在深海水（DSW）混合实验中检查了表层水微微型浮游生物组合的短期转录反应。流式细胞术和转录组分析均表明，与对照相比，在 DSW 处理的样品中，12 小时后，DSW 处理的样品中类似于交替单胞菌的种群得到了刺激。在 DSW 处理的样品中高度表达的交替单胞菌转录本中，与趋化作用、细胞运动和碳代谢相关的基因的表达最为丰富，而与对照相比则相对较少。同样，与对照相比，聚球藻表现出与碳固定和光合作用相关的基因的转录水平显著升高，以及细胞密度略有增加。尽管其他微生物类群没有表现出增强的生长，但 DSW 刺激其全基因组转录谱的变化仍然很容易检测到。细胞相关的蓝藻噬菌体 DNA 和 cDNA 图谱表明 DSW 刺激了噬菌体介导的细胞裂解，而这些细胞先前已被感染。将 DSW 响应的交替单胞菌种群与之前报道的对溶解有机物质（DOM）响应的交替单胞菌（McCarren 等人，2010）进行比较，发现了转录本丰度的差异，主要是在移动元件和噬菌体相关基因的编码基因之间。两种不同处理中，其他代谢途径中的转录本表示在两个不同处理的交替单胞菌种群之间存在显著差异，这表明 DSW 和 DOM 对特定代谢途径的扰动有特定的代谢反应。总的来说，这些结果为微微型浮游生物对 DSW 混合的短期反应提供了新的见解，这些反应发生在更大的浮游植物物种更为人熟知的、更长期的生长反应之前。
