POSTER: Rapid response of Microcystis aeruginosa bloom microbiome to high concentration hydrogen peroxide
Research Mentor: Dr. Hidetoshi Urakawa
Additional Authors: Elizabeth Dahedl, Michael Kratz, Julia Davis
Abstract:
Hydrogen peroxide has recently gained popularity as an environmentally friendly treatment for cyanobacterial harmful algal blooms (HABs). Low concentration applications in lentic systems have proven effective with desirable outcomes as the treatment degrades into water and oxygen, and does not harm non-target aquatic life. However, the general populace desires rapid removal of HABs. High concentration hydrogen peroxide can achieve this but may introduce an increased risk to the environment. Most susceptible is the microbial community, with hydrogen peroxide noted to have temporary but recoverable impacts at low concentration treatments. This is concerning as recently the importance of HAB-associated microorganisms has been highlighted, shown to directly impact HAB succession and nutrient modulation. Currently, there is a gap between small-scale laboratory experiments and real world field studies of high concentration applications and impacts to the microbial community. A mesocosm study provides the necessary bridge to further our understanding. In this study we used a high concentration hydrogen peroxide treatment of a Microcystis aeruginosa HAB to examine impacts on microbial community succession and the resulting effects on nutrient modulation and toxin degradation. Over the course of four days in May 2021, we monitored M. aeruginosa bloom biomass retrieved from Lake Okeechobee in six mesocosms filled with 300 L of sieved river water on the bank of the Caloosahatchee River at Franklin Lock and Dam. Our treatment group consisted of three mesocosms which received a hydrogen peroxide spray treatment of 130x the lethal dose for M. aeruginosa (theoretical concentration of 13 mM; 15.7 mM measured). This treatment successfully achieved rapid (< 24 hour) bloom collapse. The treated microbial community exhibited drastic change, with a steady increase in Planctomycetes (0.58% to 46.85%) and Gammaproteobacteria (0.81% to 17.38%) relative abundance post-treatment. The treatment group also saw extreme increases of ammon ia (13.9x higher) and nitrate/nitrite (14.5x higher), and fluctuations in organic phosphorous when compared to the control. There was no clear evidence of cyanotoxin or hydrogen peroxide degradation beyond the expected increase of extracellular microcystin due to cell lysing from treatment. Our study identified microbial components of a South Florida M. aeruginosa bloom resilient to hydrogen peroxide. Theses taxa are different from previously reported hydrogen peroxide resilient bacteria and even show opposite trends in studies from other parts of the world, decreasing after hydrogen peroxide treatment. This further highlights the importance of understanding local systems and populations with respect to water resources and HAB management.