Ecological Dynamics of Toxic Microcystis spp. and Microcystin-Degrading Bacteria in Dianchi Lake, China

Abstract

bToxic cyanobacterial blooms directly threaten both human safety and the ecosystem of surface waters. The widespread occurrence of these organisms, coupled with the tumor-promoting properties of the microcystin toxins that they produce, demands action to mitigate their potential impacts and, thus, a robust understanding of their ecological dynamics. In the present work, the abundance of toxic Microcystis spp. and microcystin (MC)-degrading bacteria in Dianchi Lake, located in Yunnan Province, China, was studied using quantitative PCR. Samples were taken at monthly intervals from June 2010 to December 2011 at three sampling stations within this freshwater lake. Results revealed that variation in the abundance of both total Microcystis spp. and toxic Microcystis spp. exhibited similar trends during the period of the algal bloom, including the reinvasion, pelagic growth, sedimentation, and overwintering periods, and that the proportion of toxic Microcystis was highest during the bloom and lowest in winter. Importantly, we observed that peaks in mlrA gene copy numbers of MC-degrading bacteria occurred in the months following observed peaks in MC concentrations. To understand this phenomenon, we added MCs to the MC-degrading bacteria (designated strains HW and SW in this study) and found that MCs significantly enhanced mlrA gene copy numbers over the number for the control by a factor of 5.2 for the microcystin-RR treatment and a factor of 3.7 for the microcystin-LR treatment. These results indicate that toxic Microcystis and MC-degrading bacteria exert both direct and indirect effects on each other and that MC-degrading bacteria also mediate a shift from toxic to nontoxic populations of Microcystis.

Presence or Absence of mlr Genes and Nutrient Concentrations Co-Determine the Microcystin Biodegradation Efficiency of a Natural Bacterial Community

“…Similar results were observed by Zhu et al (2014) [49], who found that seasonal variations of extracellular MCs in water were related to variations in MCs-degrading bacterial abundance based on mlr A gene analysis. Our results, together with other studies, suggest that these mlr A + bacteria make an important contribution to the biodegradation of MCs in water [49,50]. However, the real contribution of the total biodegradation of MCs in nature can only be understood by considering the whole MCs-degrading bacterial community which, according to our results, goes beyond the analysis of the mlr A gene.…”

Assessment of the factors contributing to the variations in microcystins biodegradability of the biofilms on a practical biological treatment facility

“…3a). This result was consistent with Zhu et al (2014), who also revealed that the mlrA gene copy number exhibited peak in the months following observed peaks of MCs concentration and water temperature in Dianchi Lake, China. The phenomenon here implied that MCLR in water column where biofilms submerged can act as nutrient sources for growth of MC-degrader population in biofilms.…”

Role of bacteria in the production and degradation of Microcystis cyanopeptides

“…; Zhu et al. ). Sphingomonadales species are well adapted to the cyanobacterial phycosphere, especially that of Microcystis with regard to their capacity to degrade cyanobacterial toxins and other problematic organic compounds (Wilkes et al.…”