Prophylactic Addition of Glucose Suppresses Cyanobacterial Abundance in Lake Water.

Stephen Vesper,Jingrang Lu,Nathan Sienkiewicz,David Linz,Ian Struewing

doi:10.3390/life12030385

Abstract

To mitigate harmful cyanobacterial blooms (HCBs), toxic algicides have been used, but alternative methods of HCB prevention are needed. Our goal was to test the prophylactic addition of glucose to inhibit HCB development, using Microcystis and the toxin microcystin as the HCB model. Water samples were collected weekly, from 4 June to 2 July, from Harsha Lake in southwestern Ohio during the 2021 algal bloom season. From each weekly sample, a 25 mL aliquot was frozen for a 16S rRNA gene sequencing analysis. Then, 200 mL of Harsha Lake water was added to each of the three culture flasks, and glucose was added to create concentrations of 0 mM (control), 1.39 mM, or 13.9 mM glucose, respectively. The microcystin concentration in each flask was measured after 1 and 2 weeks of incubation. The results showed an 80 to 90% reduction in microcystin concentrations in glucose-treated water compared to the control. At the end of the second week of incubation, a 25 mL sample was also obtained from each of the culture flasks for molecular analysis, including a 16S rRNA gene sequencing and qPCR-based quantification of Microcystis target genes. Based on these analyses, the glucose-treated water contained significantly lower Microcystis and microcystin producing gene (mcy) copy numbers than the control. The 16S rRNA sequencing analysis also revealed that Cyanobacteria and Proteobacteria were initially the most abundant bacterial phyla in the Harsha 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’s relative abundance, Microcystis numbers and microcystin concentrations and increased the relative abundance of Proteobacteria compared to the control.

Highlights

Harmful cyanobacterial blooms (HCBs), and the toxins they produce, are a threat to the safety of drinking and recreational water and the aquatic ecosystem [1,2]
The culture flasks with a final glucose concentration of either 1.39 mM or 13.9 mM glucose contained significantly (Student t-test, p < 0.05) lower concentrations of microcystin each week compared to the control
These differences in microcystin concentrations were further supported by quantifying Microcystis toxin gene copy number by qPCR

Summary

Introduction

Harmful cyanobacterial blooms (HCBs), and the toxins they produce, are a threat to the safety of drinking and recreational water and the aquatic ecosystem [1,2]. To prevent HCBs, it is necessary to limit the introduction of high concentrations of fixed nitrogen compounds and phosphates [3]. Agents or methods are needed that can limit the production of cyanotoxins. Most HCB control measures involve the addition of an algicide once the bloom has developed. Many HCB control agents can reduce cyanotoxin concentrations but these algicides are dangerous to handle and toxic. Algicides usually contain hydrogen peroxide, sometimes combined with an acid such as peroxyacetic acid, or the algicide is a formulation of copper (Cu) [4–7]. Hydrogen peroxide is toxic at high concentrations and is a strong oxidizer, which makes it dangerous to handle [8]. Copper is a toxic metal that can bioaccumulate in freshwater ecosystems [9].

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Conclusion