Phosphorus accelerate the sulfur cycle by promoting the release of malodorous volatile organic sulfur compounds from Microcystis in freshwater lakes

Volatile organic sulfur compounds (VSCs) released by algae are of great significance in sulfur cycle, climate regulation and biological information transmission, and they also caused taste and odor in freshwaters. However, the categories, sources, and environmental regulatory factors of VSCs in freshwaters were less known. Here, we show that eight com-mon freshwater cyanobacterium Microcystis, which bloom in freshwaters over the world, are found to be important producers of VSCs. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and isopropyl methyl sulfide (IPMS) are the main VSCs with the highest concentrations 184.81 nmol/L, 162.01 nmol/L and 101.55 nmol/L, respectively. The amount of VSCs released from those Microcystis varied greatly, M. elabens, M. panniformis and M. flos-aquae released the largest amount of VSCs (1260.52 nmol S/L, 1154.75 nmol S/L and 670.58 nmol S/L), and M. wesenbergii had the smallest release amount. We also found for the first time that phosphorus (P) was one of the important factors for the regulation VSCs from most Microcystis. P can elevate the release of DMS by promoting the biomass and DMS yields of most Microcystis in the range 0.05 mg/L to 0.5 mg/L. Similar results were also found in 16 lakes at three dif-ferent spatiotemporal scales. Overall, we revealed that the common freshwater Microcystis were able to release diverse thioethers, and the major VSCs were significantly influenced by water P concentrations. In the context of global fresh-water eutrophication and Microcystis bloom, freshwater cyanobacteria driven sulfur cycle and water odor will probably be further strengthened.

Automated summary

This study revealed that common freshwater cyanobacterium Microcystis are important producers of volatile organic sulfur compounds (VSCs) in freshwaters. Dimethyl sulfide, dimethyl disulfide, and isopropyl methyl sulfide were identified as the main VSCs. Phosphorus was found to be one of the key factors regulating VSCs production. These findings are significant for understanding the categories, sources, and environmental regulatory factors of VSCs in freshwaters, as well as the impact of freshwater eutrophication and Microcystis blooms on sulfur cycle and water odor.