Prophylactic glucose addition to Lake water suppresses Cyanobacteria abundance

To mitigate harmful cyanobacterial blooms (HCBs), toxic algicides have been used but alternative methods of HCBs prevention are needed. Our goal was to test the prophylactic addition of glucose to inhibit HCBs development, using Microcystis and the toxin microcystin as the HCBs model. Water samples were collected weekly, June 4 through July 2, from Harsha Lake in southwestern Ohio during the 2021 algal-bloom season. Glucose was added to make concentrations of 0 mM (control), 1.39 mM, or 13.9 mM glucose. The microcystin concentration in each flask was measured after 1- and 2-weeks incubation. The result was 80 to 90% lower microcystin concentrations in glucose treated water compared to the control. At the end of the 2nd week of incubation, a 25 ml sample was also obtained from each of the culture flasks for genomic analysis including 16S rRNA metagenomic sequencing and qPCR-based quantification of Microcystis target genes. Based on these analyses, the glucose treated water contained significantly lower Microcystis and the microcystin producing gene (mcy) copy numbers than the control. The metagenomic analysis also revealed that Cyanobacteria and Proteobacteria were initially the most abundant bacterial phyla in the lake water but, as the summer progressed, Cyanobacteria became the dominant phyla. However, in the glucose treated water, the Cyanobacteria decreased and the Proteobacteria increased in weekly abundance compared to the control. This glucose-induced proteobacterial increase in abundance was driven primarily by increases in two distinct families of Proteobacteria: Devosiaceae and Rhizobiaceae. In conclusion, the prophylactic addition of glucose to Harsha Lake water samples reduced Cyanobacteria abundance, Microcystis numbers and microcystin concentrations and increased the abundance of Proteobacteria compared to the control.