The Effect of a Combined Hydrogen Peroxide-MlrA Treatment on the Phytoplankton Community and Microcystin Concentrations in a Mesocosm Experiment in Lake Ludoš

Abstract

Harmful cyanobacteria and their toxic metabolites constitute a big challenge for the production of safe drinking water. Microcystins (MC), chemically stable hepatotoxic heptapeptides, have often been involved in cyanobacterial poisoning incidents. A desirable solution for cyanobacterial management in lakes and ponds would eliminate both excess cyanobacteria and the MC that they potentially produce and release upon lysis. Hydrogen peroxide (H 2 O 2 ) has recently been advocated as an efficient means of lysing cyanobacteria in lakes and ponds, however H 2 O 2 (at least when used at typical concentrations) cannot degrade MC in environmental waters. Therefore, mesocosm experiments combining the cyanobacteria-lysing effect of H 2 O 2 and the MC-degrading capacity of the enzyme MlrA were set up in the highly eutrophic Lake Ludoš (Serbia). The H 2 O 2 treatment decreased the abundance of the dominant cyanobacterial taxa Limnothrix sp., Aphanizomenon flos-aquae, and Planktothrix agardhii. The intracellular concentration of MC was reduced/eliminated by H 2 O 2 , yet the reduction of the extracellular MC could only be accomplished by supplementation with MlrA. However, as H 2 O 2 was found to induce the expression of mcyB and mcyE genes, which are involved in MC biosynthesis, the use of H 2 O 2 as a safe cyanobacteriocide still requires further investigation. In conclusion, the experiments showed that the combined use of H 2 O 2 and MlrA is promising in the elimination of both excess cyanobacteria and their MC in environmental waters. Key Contribution:A new concept has been proposed for rapid and efficient mitigation of MC-producing cyanobacterial biomass through a combined treatment with H 2 O 2 and microcystinase (MlrA).

Suppressing Cyanobacteria with Hydrogen Peroxide Is More Effective at High Light Intensities

“…This is consistent with the lake treatment of Matthijs et al [27], where MC disappeared in 1-2 days after H 2 O 2 addition. In addition, H 2 O 2 treatments supplemented with the MC-degrading enzyme Mlr-A can further enhance the degradation of MC released by lysing cyanobacteria [97]. Whether interactions between H 2 O 2 and high light intensities affect this microbial degradation of MC is an interesting open question that may deserve further attention in future studies.…”

Protected Freshwater Ecosystem with Incessant Cyanobacterial Blooming Awaiting a Resolution

“…Results showed that the treatment decreased the abundance of the dominant cyanobacterial taxa and reduction of the intracellular concentration of MC by H 2 O 2 , but the reduction of the extracellular MC was not accomplished in combination with MlrA. Since H 2 O 2 was found to induce the expression of mcyB and mcyE genes involved in MC biosynthesis, the use of H 2 O 2 as a safe cyanobacteriocide still requires further investigation [101]. Several other authors have also suggested measures for water-quality improvement of this lake, including the identification of source water with lower nutrient content for maintaining the volume of the lake, sediment removal [102,103], and sediment phytoremediation [104].…”

Effects of Microcystin-LR on Metabolic Functions and Structure Succession of Sediment Bacterial Community under Anaerobic Conditions

“…The mlr gene cluster is acknowledged as MC-degrading gene, comprising mlrA, mlrB, mlrC, and mlrD, which can express Mlr enzymes to sequentially degrade MC-LR, linearized MC-LR, and tetrapeptide [56,57]. Among them, mlrA is regarded as the most important one, which encode metalloprotease MlrA [58]. Bourne et al first found that microcystinase MlrA can hydrolyze cyclic MC-LR to linearized MC-LR through breaking the peptide bond at Arg-Adda [56,57].…”