In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then accumulate on sediments, leading to the formation of biological fluid sediment. In this study, the formation process of biological fluid sediment was investigated in microcosm experiments by monitoring the variations in gas, sediment physicochemical properties, and microorganisms during 30 days. It was found that variations in sediment height reached the maximum value on day 8 (0.53 cm) with the minimum sediment density (1.04 g cm–3). Meanwhile, the amount of carbon dioxide (CO2) produced through fermentation was larger than methane (CH4) during the initial 4 days. Then, the amount of CH4 drastically increased, resulting in the release of gas from sediments. In addition, a high amount of extracellular polymer substances (EPSs) was produced and led to sediment particle agglomeration, which benefited in maintaining the structure of biological fluid sediment. Through the microbial community analysis, it was found that the strong symbiotic structure of the microbial community in the early stage provided favorable conditions for the formation of CH4 in sediments. The results of this study can clarify the formation mechanism of biological fluid sediment and provide help for understanding the effect of biogas and secretions on the sediment properties in shallow lakes.
Abstract Bacteria play key roles in the function and diversity of aquatic systems, but aside from study of specific bloom systems, little is known about the diversity or biogeography of bacteria associated with harmful cyanobacterial blooms (cyanoHABs). CyanoHAB species are known to shape bacterial community composition and to rely on functions provided by the associated bacteria, leading to the hypothesized cyanoHAB interactome, a coevolved community of synergistic and interacting bacteria species, each necessary for the success of the others. Here, we surveyed the microbiome associated with Microcystis aeruginosa during blooms in 12 lakes spanning four continents as an initial test of the hypothesized Microcystis interactome. We predicted that microbiome composition and functional potential would be similar across blooms globally. Our results, as revealed by 16S rRNA sequence similarity, indicate that M. aeruginosa is cosmopolitan in lakes across a 280° longitudinal and 90° latitudinal gradient. The microbiome communities were represented by a wide range of operational taxonomic units and relative abundances. Highly abundant taxa were more related and shared across most sites and did not vary with geographic distance, thus, like Microcystis , revealing no evidence for dispersal limitation. High phylogenetic relatedness, both within and across lakes, indicates that microbiome bacteria with similar functional potential were associated with all blooms. While Microcystis and the microbiome bacteria shared many genes, whole‐community metagenomic analysis revealed a suite of biochemical pathways that could be considered complementary. Our results demonstrate a high degree of similarity across global Microcystis blooms, thereby providing initial support for the hypothesized Microcystis interactome.
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