刚毛藻腐烂过程中溶解性有机物的释放和细菌群落的变化

通过室内培养模拟了高密度刚毛藻聚积腐烂过程,研究了刚毛藻在不同腐烂时间段下的溶解性有机物(DOM)的释放和附着微生物的群落变化。结果表明:在40d的分解实验中,刚毛藻生物量(干重)减少,且表现为前期损失快,后期损失减缓的趋势。在实验结束时(40d),干物质残留率为43.15%,质量损失了56.85%。在刚毛藻分解过程中, DOM在7—10d内快速释放达到最大值,而后降低。DOM的组分也变得复杂,荧光峰从区域Ⅰ、Ⅱ和Ⅳ逐渐转移到区域Ⅲ和Ⅴ。大量的简单芳香蛋白,如酪氨酸类物质被微生物转化为各种代谢物,并产生了腐殖质类物质。刚毛藻附着微生物优势菌为变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes),相对丰度分别为6.54%—71.62%、16.83%—55.50%和0.95%—20.91%。在腐烂过程的不同阶段中,微生物的组成差异显著,表现为前期主要是Proteobacteria占主导优势,实验后期是Bacteroidetes占主导优势,细菌群落的演替与DOM组成的变化相关。

DISSOLVED ORGANIC MATTER RELEASE AND BACTERIAL COMMUNITY SHIFTS DURING THE DECOMPOSITION OF CLADOPHORA

The Cladophora overgrowth has become a widespread global problem. The decomposition of Cladophora biomass releases large amounts of dissolved organic matter (DOM), a key substance in the biogeochemical cycle of carbon in aquatic ecosystems, resulting in a more complex organic pollution in water bodies. Field investigations and indoor experiments have proven that one of the sources of endogenous DOM in water bodies is the biodegradation of algae. Microorganisms play an important role in the decay of aquatic plants, and bacteria differ in their metabolic preferences and affinity for substrates. Bacterial diversity and community composition may both influence and respond to changes in DOM. However, it is not clear how the microbial community and the DOM composition of the surrounding water column change during the decomposition of the Cladophora. In order to study the composition of algal-derived DOM, we simulated the decay process of Cladophora in the laboratory. The experiment was carried out in a constant temperature incubator. 10 g (fresh weight) of Cladophora was placed into sterile polyethylene plastic bottles with 500 mL of sterile water and placed in dark conditions at 25℃ to decay naturally. Three replicate samples were randomly selected for chemical and microbiological analysis at 1, 4, 7, 10, 15, 20, 30 and 40 days. We performed 16S amplicon sequencing of algal-attached microorganisms to analyse the dynamic process of microbial self-assembly on decaying algae. The results showed that during the 40-day decomposition experiment, the biomass of Cladophora decreased, and it showed a trend of rapid loss in the early stages and slowed down in the later stages. At the end of the experiment (40 days), the dry matter residual rate was 43.15% and the mass loss was 56.85%. During the decomposition process of Cladophora, DOM quickly released to the maximum within 7—10 days. The composition of DOM also became complicated, and the fluorescence peaks gradually shifted from regions Ⅰ, Ⅱ and Ⅳ to regions Ⅲ and Ⅴ. A large amount of simple aromatic proteins, such as tyrosine, were transformed into various metabolites by microorganisms, and humic substances were produced. The dominant phyla of microorganisms attached to the Cladophora were Proteobacteria, Bacteroidetes and Firmicutes, with relative abundances ranging from 6.54% to 71.62%, 16.83% to 55.50% and 0.95% to 20.91%, respectively. In different stages of the decay process, the composition of microorganisms was significantly different, which was mainly dominated by Proteobacteria in the early stage and Bacteroidetes in the late stage of the experiment. Pearson's correlation (R=0.81, P=0.001) between Bray-Curtis distance and Euclidean distance of DOM composition for bacterial communities was calculated using the Mantel test (999 ranking). The results of the Mantel test indicated that changes in DOM composition were significantly correlated with changes in the composition of the bacterial community. These findings have implications for further understanding of the characteristics of DOM released during the decay of Cladophora blooms and the relationship between DOM and microbial communities, and provide theoretical support for the management of filamentous green algae blooms.