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Published on: December 19, 2019
Tolerance and resistance characteristics of microalgae Scenedesmus sp. LX1 to methylisothiazolinone
Xiao-Xiong Wang1, Tian-Yuan Zhang2, Guo-Hua Dao2
1Environmental Simulation and Pollution Control State Key Joint Laboratory, School of Environment, Tsinghua University, Beijing, 100084, PR China; State Environmental Protection Key Laboratory of Microorganism Application and Risk Control, Graduate School at Shenzhen, Tsinghua University, Shenzhen, 518055, PR China.
Abstract:
Methylisothiazolinone (MIT) has been widely used to control bacterial growth in reverse osmosis (RO) systems. However, MIT's toxicity on microalgae should be determined because residual MIT is concentrated into RO concentrate (ROC) and might have a severe impact on microalgae-based ROC treatment. This study investigated the tolerance of Scenedesmus sp. LX1 to MIT and revealed the mechanism of algal growth inhibition and toxicity resistance. Scenedesmus sp. LX1 was inhibited by MIT with a half-maximal effective concentration at 72 h (72 h-EC50) of 1.00 mg/L, but the strain recovered from the inhibition when its growth was not completely inhibited. It was observed that this inhibition's effect on subsequent growth was weak, and the removal of MIT was the primary reason for the recovery. Properly increasing the initial algal density significantly shortened the adaptation time for accelerated recovery in a MIT-containing culture. Photosynthesis damage by MIT was one of the primary reasons for growth inhibition, but microalgal cell respiration and adenosine triphosphate (ATP) synthesis were not completely inhibited, and the algae were still alive even when growth was completely inhibited, which was notably different from observations made with bacteria and fungi. The algae synthesized more chlorophyll, antioxidant enzymes of superoxide dismutase (SOD) and catalase (CAT), and small molecules, such as reduced glutathione (GSH), to resist MIT poisoning. The microalgae-based process could treat the MIT-containing ROC, since MIT was added for only several hours a week in municipal wastewater reclamation RO processes, and the MIT average concentration was considerably lower than the maximum concentration that algae could tolerate.
Insights
Methylisothiazolinone (MIT) inhibits microalgae growth, but Scenedesmus sp. LX1 can recover by removing MIT. Algae resist MIT toxicity by synthesizing protective compounds, indicating potential for microalgae-based treatment of MIT-containing wastewater concentrate.
Area of Science:
- Environmental microbiology
- Ecotoxicology
- Biotechnology
Background:
- Methylisothiazolinone (MIT) is a biocide used in reverse osmosis (RO) systems.
- Residual MIT concentrates in RO concentrate (ROC), posing risks to microalgae-based treatment.
- Understanding MIT's impact on microalgae is crucial for effective ROC management.
Purpose of the Study:
- To investigate the tolerance of Scenedesmus sp. LX1 to MIT.
- To elucidate the mechanisms of MIT-induced growth inhibition and algal resistance.
- To assess the feasibility of microalgae for treating MIT-contaminated ROC.
Main Methods:
- Determining the 72-hour half-maximal effective concentration (EC50) of MIT for Scenedesmus sp. LX1.
- Observing algal recovery after MIT exposure and assessing the role of MIT removal.
- Analyzing the effects of initial algal density on recovery time.
- Investigating the impact of MIT on photosynthesis, respiration, and ATP synthesis.
- Measuring the synthesis of protective compounds like chlorophyll, SOD, CAT, and GSH.
Main Results:
- Scenedesmus sp. LX1 exhibited a 72h-EC50 of 1.00 mg/L for MIT, with significant recovery observed upon MIT removal.
- Increased initial algal density accelerated recovery from MIT inhibition.
- MIT primarily damaged photosynthesis, but respiration and ATP synthesis persisted, allowing survival even at complete growth inhibition.
- Algae synthesized increased chlorophyll, antioxidant enzymes (SOD, CAT), and GSH to counteract MIT toxicity.
- MIT average concentrations in municipal wastewater reclamation ROC were below the tolerance threshold for microalgae.
Conclusions:
- Scenedesmus sp. LX1 demonstrates tolerance and recovery mechanisms against MIT, including MIT biodegradation and synthesis of protective compounds.
- Microalgae can potentially treat MIT-contaminated ROC, as short-term MIT application in RO systems results in concentrations below inhibitory levels.
- This study supports the viability of microalgae-based processes for managing wastewater containing biocides like MIT.
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