Widespread Distribution and Adaptive Degradation of Microcystin Degrader (mlr-Genotype) in Lake Taihu, China

Abstract

Microbial degradation is an important route for removing environmental microcystins (MCs). Here, we investigated the ecological distribution of microcystin degraders (mlr-genotype), and the relationship between the substrate specificity of the microcystin degrader and the profile of microcystin congener production in the habitat. We showed that microcystin degraders were widely distributed and closely associated with Microcystis abundance in Lake Taihu, China. We characterized an indigenous degrader, Sphingopyxis N5 in the northern Lake Taihu, and it metabolized six microcystin congeners in increasing order (RR > LR > YR > LA > LF and LW). Such a substrate-specificity pattern was congruent to the order of the dominance levels of these congeners in northern Lake Taihu. Furthermore, a meta-analysis on global microcystin degraders revealed that the substrate-specificity patterns varied geographically, but generally matched the profiles of microcystin congener production in the degrader habitats, and the indigenous degrader typically metabolized well the dominant MC congeners, but not the rare congeners in the habitat. This highlighted the phenotypic congruence between microcystin production and degradation in natural environments. We theorize that such congruence resulted from the metabolic adaptation of the indigenous degrader to the local microcystin congeners. Under the nutrient microcystin selection, the degraders might have evolved to better exploit the locally dominant congeners. This study provided the novel insight into the ecological distribution and adaptive degradation of microcystin degraders.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

“…More than 120 taxa of viruses, bacteria, microfungi, heterotrophic protists, and several eukaryotic microalgae negatively affect Microcystis growth [ 143 ]. The strains of the bacterial genera Sphingomonas (majority of MC-degrading bacteria), Rhodococcus , Brevibacterium , Burkholderia , Mycobacterium , Pseudomonas , Novosphyngobium and others can degrade MCs in time scale from hours to days [ 144 , 145 , 146 , 147 , 148 , 149 ]. The genomes of some MCs-degrading bacteria are sequenced [ 150 , 151 ], and mlr gene cluster have been implicated in playing a prominent role in the sequential hydrolysis of MCs peptide bonds [ 151 , 152 ].…”