Transparent exopolymer particles (TEP) are mainly acidic polysaccharides directly or indirectly formed by phytoplankton and bacteria. These particles are often colonized by picoplankton and considered a hot spot for microbial activity. Recent studies suggested an important role of Synechococcus in TEP production found in lakes and prompted us to further investigate this issue using monoclonal xenic cultures of Synechococcus. We tested TEP production under oxidative stress in two treatments, one with hydrogen peroxide and another treated with ultraviolet radiation (UVR) and high photosynthetic active radiation (PAR), compared with an unstressed control. Our results showed a cell-normalized TEP production, ranging from 12 to 238 ng C cell–1 among strains, not only under stress but also in the control with non-limiting nutrients. Our data prove that freshwater communities of Synechococcus and their associated heterotrophic microflora, are capable of producing TEP even during growth phase. The oxidative stress induced extra production of TEP up to 400 ng C cell–1 in one of our phycocyanin-type (PC) strain. The phycoerythrin-type (PE) strains increased TEP production, particularly under UV-PAR stress, whereas the PC strains did it under H2O2 stress. This study provides new perspectives on the potential role of freshwater Synechococcus in TEP production.

中文翻译：

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聚球蓝细菌氧化应激下的 TEP 产生

透明外聚体颗粒（TEP）主要是由浮游植物和细菌直接或间接形成的酸性多糖。这些颗粒通常被微型浮游生物定殖，并被认为是微生物活动的热点。最近的研究表明聚球藻在湖泊中发现的 TEP 生产中发挥着重要作用，并促使我们使用聚球藻的单克隆异种培养物进一步研究这个问题。我们测试了两种处理中氧化应激下 TEP 的产生，一种使用过氧化氢，另一种使用紫外线辐射 (UVR) 和高光合活性辐射 (PAR) 处理，与未受胁迫的对照相比。我们的结果显示细胞标准化的 TEP 产量，在菌株之间从 12 到 238 ng C cell-1，不仅在压力下，而且在非限制性营养物的控制下也是如此。我们的数据证明，即使在生长阶段，聚球藻的淡水群落及其相关的异养微生物群落也能够产生 TEP。氧化应激在我们的一种藻蓝蛋白型 (PC) 菌株中诱导额外产生高达 400 ng C cell-1 的 TEP。藻红蛋白型 (PE) 菌株增加了 TEP 的产生，特别是在 UV-PAR 胁迫下，而 PC 菌株在 H2O2 胁迫下增加了。这项研究为淡水聚球藻在 TEP 生产中的潜在作用提供了新的视角。特别是在 UV-PAR 压力下，而 PC 菌株在 H2O2 压力下做到了。这项研究为淡水聚球藻在 TEP 生产中的潜在作用提供了新的视角。特别是在 UV-PAR 压力下，而 PC 菌株在 H2O2 压力下做到了。这项研究为淡水聚球藻在 TEP 生产中的潜在作用提供了新的视角。