Abstract
Microcystins (MCs), which are produced by harmful cyanobacteria blooms, pose a serious threat to environmental health. However, the effect of MCs on the bacterial community under anaerobic conditions is still unclear. This study examined the dynamic changes of MC-degrading capacity, metabolic activity, and structure of the bacterial community in lake sediment repeatedly treated with 1 mg/L microcystin-LR (MC-LR) under anaerobic conditions. The results showed that the MC-degrading capacity of the bacterial community was increased nearly three-fold with increased treatment frequency. However, the metabolic profile behaved in exactly opposite trend, in which the overall carbon metabolic activity was inhibited by repeated toxin addition. Microbial diversity was suppressed by the first addition of MC-LR and then gradually recovered. The 16S amplicon sequencing showed that the dominant genera were changed from Exiguobacterium and Acinetobacter to Prosthecobacter, Dechloromonas, and Agrobacterium. Furthermore, the increase in the relative abundance of Dechloromonas, Pseudomonas, Hydrogenophaga, and Agrobacterium was positively correlated with the MC-LR treatment times. This indicates that they might be responsible for MC degradation under anaerobic conditions. Our findings reveal the relationship between MC-LR and the sediment bacterial community under anaerobic conditions and indicate that anaerobic biodegradation is an effective and promising method to remediate MCs pollution.
Highlights
The heavy occurrence of harmful cyanobacterial blooms has become a global environmental problem due to producing a series of cyanotoxins such as microcystins (MCs), nodularins, and cylindrospermopsins [1,2]
The ability to ability to degrade MC-LR by the continuously treated bacterial community was assessed by degrade MC-LR by the continuously treated bacterial community was assessed by measuring the toxin measuring the toxin residues in the culture system (Figure 1)
Of the variance, PC2 represented 24.53%, and PC3 20.84%. These results suggest that the effect of MC-LR on the sediment bacterial community structure was weakened with the increase in treatment times under anaerobic conditions
Summary
The heavy occurrence of harmful cyanobacterial blooms has become a global environmental problem due to producing a series of cyanotoxins such as microcystins (MCs), nodularins, and cylindrospermopsins [1,2]. MCs, which account for the highest proportion of all cyanotoxins, are suggested to be involved in various biological functions, including resisting oxidative stress, nutrients acquisition and programmed cell death [3,4,5,6]. Toxins 2020, 12, 183 cells, are released to the extracellular environment due to cell death or injury of structural integrity [7]. Some variants of microcystin (MC), with a stabilized structure and severe toxicity, have often been detected in freshwater, sediment, and aquatic products, which disturb the internal balance of the aquatic ecology and pose a potential threat to public health [10]. Microcystin-LR (MC-LR) is considered to be one of the most toxic variants, classified by International Agency for Research on Cancer (IARC) as a possible human carcinogen [10,11,12]
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