Growth rates and microcystin production of Microcystis strains in response to allochthonous and autochthonous nutrient sources
Yong-Jun Kim, Kyoung-Hee Oh, Young-Cheol Cho
Environmental Analysis Health and Toxicology
This study investigated the growth dynamics and microcystin (MC) production of Microcystis in response to various autochthonous and allochthonous nutrient sources, specifically cyanobacterial scum, floating periphyton mats, sediment, and agricultural soil. Chemical analysis revealed that cyanobacterial scum is a major nitrogen reservoir (25.72 mg/g of dry weight(g dw)), while periphyton mats serve as significant phosphorus buffers through luxury uptake (1.92 mg/g dw). Laboratory cultures of <i>Microcystis</i> strains NIER10004 and CBE51 demonstrated that sediment extracts promoted the highest growth rates (0.0160 and 0.0166 OD750/d, respectively) and the greatest biomass-to-total phosphorus ratios. Phosphorus uptake followed a biphasic pattern: a rapid depletion of orthophosphate in the first 10 days, followed by a transition to organic phosphorus utilization, likely facilitated by alkaline phosphatase activity. MC concentrations peaked at the onset of the stationary phase, though total MC content showed a low correlation with the specific nutrient source, suggesting that nutrient supply primarily drives biomass expansion rather than MC biosynthesis rates. Given the feasibility of mechanical removal, artificial harvesting of periphyton mats during spring—when increased microbial activity in sediments causes the mats to detach and float—is proposed as a more viable and cost-effective management strategy than expensive sediment dredging for mitigating harmful algal blooms in eutrophic reservoirs.
Field-Based Mesocosm Evidence for the Role of Natural Nutrient Sources in Cyanobacterial Blooms
Yong-Jun Kim, Jae-Hun Lee, Young-Cheol Cho
Environmental Analysis Health and Toxicology
Harmful algal blooms (HABs) dominated by toxigenic cyanobacteria represent a growing threat to freshwater ecosystems and drinking water security. While phosphorus is widely recognized as a key driver of cyanobacterial proliferation, the ecological roles of naturally derived nutrient sources remain poorly understood. In this study, field-based mesocosm experiments were conducted to compare the effects of various nutrient sources originating from both autochthonous and allochthonous origins—sediments, cyanobacterial scums, benthic periphyton mats, and agricultural soils—on cyanobacterial and <i>Microcystis</i> growth, as well as microcystin (MC) production. All nutrient treatments were adjusted to a uniform total phosphorus concentration (0.4 mg/L), and nitrogen limitation was excluded. Cyanobacterial biomass, assessed via chlorophyll-a and phycocyanin fluorescence, was consistently higher in all nutrient-amended mesocosms than in the inorganic phosphorus control. Notably, periphyton mat extracts promoted sustained biomass accumulation during the latter incubation stages. MC concentrations were elevated in all nutrient-amended treatments relative to the control, although no significant differences were observed among the various nutrient sources. Quantitative PCR analysis revealed that while total <i>Microcystis</i> abundance did not differ significantly across treatments, the abundance and relative proportion of toxigenic <i>Microcystis</i> (<i>mcyA</i> gene) were significantly higher in periphyton mat–amended mesocosms. In contrast, MC production normalized to toxigenic cell abundance showed no significant variation among treatments, indicating that strain-specific traits exert a stronger influence on toxin production than the nutrient source type. These findings demonstrate that organically derived nutrient sources, particularly periphyton mats, play a critical role in sustaining HABs and selectively promoting toxigenic strains. Consequently, effective HAB mitigation strategies should extend beyond simple total phosphorus reduction to include the management of internal nutrient sources and phosphorus speciation within aquatic systems.
Growth rates and microcystin production of Microcystis strains in response to allochthonous and autochthonous nutrient sources
Yong-Jun Kim, Kyoung-Hee Oh, Young-Cheol Cho
Environmental Analysis Health and Toxicology
This study investigated the growth dynamics and microcystin (MC) production of Microcystis in response to various autochthonous and allochthonous nutrient sources, specifically cyanobacterial scum, floating periphyton mats, sediment, and agricultural soil. Chemical analysis revealed that cyanobacterial scum is a major nitrogen reservoir (25.72 mg/g of dry weight(g dw)), while periphyton mats serve as significant phosphorus buffers through luxury uptake (1.92 mg/g dw). Laboratory cultures of <i>Microcystis</i> strains NIER10004 and CBE51 demonstrated that sediment extracts promoted the highest growth rates (0.0160 and 0.0166 OD750/d, respectively) and the greatest biomass-to-total phosphorus ratios. Phosphorus uptake followed a biphasic pattern: a rapid depletion of orthophosphate in the first 10 days, followed by a transition to organic phosphorus utilization, likely facilitated by alkaline phosphatase activity. MC concentrations peaked at the onset of the stationary phase, though total MC content showed a low correlation with the specific nutrient source, suggesting that nutrient supply primarily drives biomass expansion rather than MC biosynthesis rates. Given the feasibility of mechanical removal, artificial harvesting of periphyton mats during spring—when increased microbial activity in sediments causes the mats to detach and float—is proposed as a more viable and cost-effective management strategy than expensive sediment dredging for mitigating harmful algal blooms in eutrophic reservoirs.
Field-Based Mesocosm Evidence for the Role of Natural Nutrient Sources in Cyanobacterial Blooms
Yong-Jun Kim, Jae-Hun Lee, Young-Cheol Cho
Environmental Analysis Health and Toxicology
Harmful algal blooms (HABs) dominated by toxigenic cyanobacteria represent a growing threat to freshwater ecosystems and drinking water security. While phosphorus is widely recognized as a key driver of cyanobacterial proliferation, the ecological roles of naturally derived nutrient sources remain poorly understood. In this study, field-based mesocosm experiments were conducted to compare the effects of various nutrient sources originating from both autochthonous and allochthonous origins—sediments, cyanobacterial scums, benthic periphyton mats, and agricultural soils—on cyanobacterial and <i>Microcystis</i> growth, as well as microcystin (MC) production. All nutrient treatments were adjusted to a uniform total phosphorus concentration (0.4 mg/L), and nitrogen limitation was excluded. Cyanobacterial biomass, assessed via chlorophyll-a and phycocyanin fluorescence, was consistently higher in all nutrient-amended mesocosms than in the inorganic phosphorus control. Notably, periphyton mat extracts promoted sustained biomass accumulation during the latter incubation stages. MC concentrations were elevated in all nutrient-amended treatments relative to the control, although no significant differences were observed among the various nutrient sources. Quantitative PCR analysis revealed that while total <i>Microcystis</i> abundance did not differ significantly across treatments, the abundance and relative proportion of toxigenic <i>Microcystis</i> (<i>mcyA</i> gene) were significantly higher in periphyton mat–amended mesocosms. In contrast, MC production normalized to toxigenic cell abundance showed no significant variation among treatments, indicating that strain-specific traits exert a stronger influence on toxin production than the nutrient source type. These findings demonstrate that organically derived nutrient sources, particularly periphyton mats, play a critical role in sustaining HABs and selectively promoting toxigenic strains. Consequently, effective HAB mitigation strategies should extend beyond simple total phosphorus reduction to include the management of internal nutrient sources and phosphorus speciation within aquatic systems.
