Abstract
Cyanobacterial blooms are a worldwide environmental problem and frequently occur in eutrophic lakes. Organophosphorus mineralization regulated by microbial alkaline phosphatase provides available nutrients for bloom regeneration. To uncover the dynamics of bacterial alkaline phosphatase activity and microbial backgrounds in relation to organophosphorus mineralization during the decomposition process of cyanobacterial blooms, the response of alkaline phosphatase PhoX-producing bacteria were explored using a 23-day mesocosm experiment with three varying densities of Microcystis biomass from eutrophic Lake Taihu. Our study found large amounts of soluble reactive phosphorus and dissolved organophosphorus were released into the lake water during the decomposition process. Bacterial alkaline phosphatase activity showed the peak values during days 5~7 in groups with different chlorophyll-a densities, and then all decreased dramatically to their initial experimental levels during the last stage of decomposition. Bacterial phoX abundances in the three experimental groups increased significantly along with the decomposition process, positively related to the dissolved organic carbon and organophosphorus released by the Microcystis blooms. The genotypes similar to the phoX genes of Alphaproteobacteria were dominant in all groups, whereas the genotypes most similar to the phoX genes of Betaproteobacteria and Cyanobacteria were also abundant in the low density (~15 μg L-1 chlorophyll-a) group. At the end of the decomposition process, the number of genotypes most similar to the phoX of Betaproteobacteria and Cyanobacteria increased in the medium (~150 μg L-1 chlorophyll-a) and high (~1500 μg L-1 chlorophyll-a) density groups. The released organophosphorus and increased bacterial phoX abundance after decomposition of Microcystis aggregates could potentially provide sufficient nutrients and biological conditions for algal proliferation and are probably related to the regeneration of Microcystis blooms in eutrophic lakes.
Highlights
Cyanobacterial blooms are a major ecological problem in many eutrophic lakes worldwide
Our study found large amounts of soluble reactive phosphorus and dissolved organophosphorus were released into the lake water during the decomposition process
A large amount of released organic matter from the decomposed cyanobacterial blooms can be transformed by bacteria into inorganic nutrients, which can be directly utilized by autotrophic organisms such as Microcystis sp. [7]
Summary
Cyanobacterial blooms are a major ecological problem in many eutrophic lakes worldwide. Bacterial community composition can be influenced by the decomposition of cyanobacterial blooms [7,8,9,10,11]. Previous studies found that a large amount of dissolved enzymatically hydrolysable phosphorus (EHP), such as phosphoric monoesters and phosphodiesters that can be hydrolysed by extracellular alkaline phosphatases (APases)-producing bacteria, were released in the decomposition of cyanobacterial blooms [14,15]. As the critical substrates for bacteria, EHP with different contents could promote or inhibit bacterial growth and APases activity [16] and alter bacterial communities during the decomposition of cyanobacterial blooms. Focus on the changes in bacterial community structure and composition during the accumulation and decomposition of cyanobacterial blooms [7,8, 11, 14,15]. Few have reported on the dynamics of APases-producing bacteria during this process
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