The development of wastewater treatment processes capable of reducing and fixing carbon is currently a hot topic in the wastewater treatment field. Microalgae possess a natural carbon-fixing advantage, and microalgae that can symbiotically coexist with indigenous bacteria in actual wastewater attract more significant attention. Ultraviolet (UV) mutagenesis and dissolved organic carbon (DOC) acclimation were applied to strengthen the carbon-fixing performance of microalgae in this study. The mechanisms associated with microalgal water purification ability, gene regulation at the molecular level and photosynthetic potential under different trophic modes resulting from carbon fixation and transformation were disclosed. The superior performance of sp. MHQ2 was eventually screened out among a large number of mutants generated from 3 wild-type strains. Results indicated that the dry cell weight of the optimal species sp. HQ mutant MHQ2 was 1.91 times that of the wild strain in the pure algal system, more carbon from municipal wastewater (MW) were transferred to the microalgae and re-entered into the biological cycle through resource utilization. In addition, COD, NH-N and TP removal efficiencies of MW by sp. MHQ2 were found to increase to 95.8% (1.1-times), 96.4% (1.4-times), and 92.9% (1.2-times), respectively, under the extra DOC supply and the assistance of indigenous bacteria in the MW. In the transcriptome analysis of the logarithmic phase, the glycolytic pathway was inhibited, and the pentose phosphate pathway was mainly carried out for microalgal life activities, further promoting efficient energy utilization. Upon analysis of carbon capture capacity and photosynthetic potential in trophic mode, the addition of NaHCO increased the photosynthetic rate of sp. MHQ2 in mixotrophy whereas it was attenuated in autotrophy. This study could provide a new perspective for the study of resource utilization and microalgae carbon- fixing mechanisms in the actual wastewater treatment process.

中文翻译：

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城市污水中新型有机固碳微藻的高碳捕获和光合作用：从诱变、筛选、能力评价到机制分析


开发能够减碳、固碳的废水处理工艺是目前废水处理领域的热点话题。微藻具有天然的固碳优势，并且能够与实际废水中的本土细菌共生共存的微藻更受关注。本研究采用紫外线（UV）诱变和溶解有机碳（DOC）驯化来增强微藻的固碳性能。揭示了微藻水净化能力、分子水平的基因调控以及不同营养模式下固碳和转化产生的光合潜力的相关机制。 sp的优越性能。最终从3个野生型菌株产生的大量突变体中筛选出MHQ2。结果表明，最佳物种的细胞干重。 HQ突变体MHQ2在纯藻系统中是野生菌株的1.91倍，更多的城市废水（MW）碳被转移到微藻中，并通过资源利用重新进入生物循环。此外，MW 的 COD、NH-N 和 TP 去除效率为 sp。在额外的 DOC 供应和 MW 中本地细菌的帮助下，MHQ2 分别增加至 95.8%（1.1 倍）、96.4%（1.4 倍）和 92.9%（1.2 倍）。在对数期转录组分析中，糖酵解途径受到抑制，磷酸戊糖途径主要进行微藻生命活动，进一步促进了能量的高效利用。通过对营养模式下碳捕获能力和光合潜力的分析，NaHCO3的添加提高了sp的光合速率。 MHQ2 在混合营养中而在自养中减弱。该研究可为实际废水处理过程中资源利用和微藻固碳机制的研究提供新的视角。