Anaerobic Degradation Pathway Of Microcystin

Toxic algae blooms associated with eutrophication are a growing environmental andhuman concern. Previous results showed that cyanobacteria which caused eutrophication canrelease toxins after death. MCs are the major cyclic heptapeptide hepatotoxin produced bycyanobacteria which significantly impair water quality and human health. Biodegradation isone of the effective methods about removal of MCs. Hence, this study focused on the analysisof the13C isotope labeled on MC-LR and investigation about the degradation of MC-LRunder anaerobic conditions and the structure of bacterial and archaeal communities with16SrRNA sequencing analysis. It was of great significance to understanding MCs’ migrationregularity, reducing the concentration of MCs and ensuring the safety of drinking water.Growth conditions of Microcystis aeruginosa (such as temperature, illumination anddifferent carbon sources) were modified. Finally25°C,55μmol(m2·s) were the proper growthand toxin production conditions. The results showed that under the same carbon concentration,organic carbon had apparent effect on the growth of Microcystis aeruginosa, the algal yield inglucose medium was6.06%higher than that in Na2CO3medium. But the content ofmicrocystin in glucose medium was not increased than that in the inorganic medium. Thecontents of several amino acids involved in the synthesis of microcystin in Na2CO3mediumwere much higher, but the content of other amino acids had the opposite trend. For protein,the contents of Microcystis aeruginosa in organic medium was387.00μg/g, was higher93.60%than the protein content of Microcystis aeruginosa in Na2CO3medium. The stablecarbon isotope was used to label the MC-LR and the results showed that it was labeled on thestructure of Glu.Microcystins were utilized to culture LW and CT microbial consortium, mainly as theirnitrogen sources at the optimum growth temperature of37°C. The degradation rate of MCs byCT microbial consortium was19.24%, higher than that in LW microbial consortium. Resultsindicated that the cyclic structure was fractured firstly, and then degraded to small molecules.The degradation products were phenylacetic acid, methane, urea, ornithine et al and ultimateproduct was methane.The structure of bacterial and archaeal communities of LW and CT microbial consortiumwere characterized by16S rRNA sequencing analysis. Results showed that phylogeneticanalysis revealed bacterial community exhibited high diversity. Spiroachaetes, Proteobacteria,Firmicutes and Candidate division WWE1existed both in CT microbial consortium and LWmicrobial consortium. For CT microbial consortium,7phyla were identified, whereCandidate division WWE1, Spiroachaetes, Deferribacteres and Proteobacteria representedthe most abundant bacterial phyla. Bacteroidetes, Proteobacteria, Spirochaetes were also themajor populations in LW microbial consortium which included4phyla. In the archaeal clonelibrary, one phyla of Euryarchaeota were identified, which played the main role on theproduction of methane. In the CT bacterial community, CT-B-10maybe was the new strain ofdegrading MC-LR.