The impact of environmental parameters on microcystin production in dialysis bag experiments.

Qingju Xue,Richard R Rediske,Brian Scull,Liqiang Xie,Nadia D Gillett,James P O’Keefe

doi:10.1038/srep38722

Abstract

It is important to understand what environmental parameters may regulate microcystin (MC) production and congener type. To determine if environmental conditions in two hydraulically connected lakes can influence MC production and congener ratios, we incubated dialysis bags containing phytoplankton from mesotrophic/eutrophic Muskegon Lake into hypereutrophic Bear Lake (Michigan, USA) and vice versa. Strong cyanobacteria growth was observed in all dialysis bags with Bear Lake phytoplankton in July and August. Phytoplankton communities were dominated by Aphanizomenon aphanizomenoides, Microcystis wesenbergii, Limnothrix redekei. MC concentrations were correlated with M. wesenbergii and A. aphanizomenoides biovolume. MC concentrations in bags incubated in the Muskegon Lake with Bear Lake water were significantly higher than the other bags. The higher light intensity and total nitrogen concentration may have caused the increase of MC production. The MC-LR/MC-RR ratios varied with sample origin but not with lake of incubation, indicating that physical environmental factors (water temperature and turbidity) were not the reasons for different toxin production ratios. Differences in total phosphorus concentrations might be one reason for the dissimilarity of the MC-LR/MC-RR ratio between the two lakes. The higher light intensity and NO3-N concentration in Muskegon Lake are two factors contributing to an increase of MC production.

Highlights

ResultsIn August, the mean concentrations of total MC (7.04 ± 0.73 μg·L−1, range: 5.77–7.97 μg·L−1) in bags in Muskegon Lake initiated with Bear Lake phytoplankton (MKBL1-3) were significantly higher than the MC in other bags (p < 0.001) (Fig. 2)
The cyanobacterial community structure, which in turn resulted in differences in the dominant MC congener and the overall toxicity
The greatest biovolume of cyanobacteria was noted in the dialysis bags incubated in Muskegon Lake with Bear Lake water (MKBL) (Fig. 1)

Summary

Results

In August, the mean concentrations of total MC (7.04 ± 0.73 μg·L−1, range: 5.77–7.97 μg·L−1) in bags in Muskegon Lake initiated with Bear Lake phytoplankton (MKBL1-3) were significantly higher than the MC in other bags (p < 0.001) (Fig. 2). Percent contributions of the MC-RR, MC-LR, and MC-YR congeners to total MC concentrations in the bags initiated with Muskegon Lake phytoplankton (MKMK1-3, BLMK1-3) ranged from 28.2–36.0%, 54.4–66.2%, and 5.06–10.7%, respectively In both months, MC concentrations correlated with the biomass of A. aphanizomenoides (R2 = 0.312, p < 0.001, Spearman’s), M. wesenbergii (R2 = 0.121, p = 0.038), L. limnetica (R2 = 0.131, p = 0.030), but not correlated with L. redekei (R2 = 0.072, p = 0.115), A. pulchra (R2 = 0.070, p = 0.121), P. limnetica (R2 = 0.000, p = 0.984) and M. aruginosa (R2 = 0.004, p = 0.735), C. raciborskii (R2 = 0.041, p = 0.239) (Table 1).

Discussion

Methods

Conclusion