Cyanotoxin impact on microbial-mediated nitrogen transformations at the interface of sediment-water column in surface water bodies Hanyan Li a , Marielle Hollstein a , Aditi Podder a , Vedansh Gupta b , Michael Barber a , Ramesh Goel a, * a Department of Civil and Environmental Engineering, University of Utah, UT, USA b Microvi Biotech Inc, Hayward, CA, USA article info Article history: Received 30 April 2020 Received in revised form 23 July 2020 Accepted 26 July 2020 Available online 6 August 2020 This paper has been recommended for acceptance by Markus Hauck. Keywords: Sediment interface Reversible kinetics Microcystin-LR Nitrifiers Kinetics amoA gene abstract Harmful cyanobacterial blooms produce lethal toxins in many aquatic ecosystems experiencing eutro- phication. This manuscript presents results on the effects of cyanotoxins on the aerobic microbial communities residing at the interface of sediments and water columns with the ammonia-oxidizing bacteria (AOB) as the model microbial community. Microcystin-LR (MC-LR), a heavily researched cya- notoxin variant, was used as the model cyanotoxin. To measure cyanotoxin influence on the activity of nitrifying microbial communities, an enriched culture of AOBs collected from an ongoing partial nitrification-nitritation reactor was examined for its exposure to 1, 5 and 10 mg/L of MC-LR. The nitri- tation kinetics experiment demonstrated MC-LR’s ability at 1, 5, and 10 mg/L concentrations to prevent ammonium oxidation with statistically significant differences in nitritation rates between the blanks and spiked samples (One-way ANOVA, p < 0.05). Significantly decreased dissolved oxygen (DO) consumption during oxygen update batch tests demonstrated toxin’s influence on AOB’s oxidizing capabilities when exposed to even lower concentrations of 0.75, 0.5, and 0.25 mg/L of MC-LR in a separate set of experi- ments. Based on competitive kinetics, the MC-LR inhibition coefficient-the concentration needed to produce half-maximum inhibition of the mixed community AOBs was determined to be 0.083 mg/L. The stress tests proved the recovery of nitritation to some extent at lower MC-LR concentrations (1 and 5 mg/ L), but significant irreversible inhibition was recorded when the AOB population was exposed to 10 mg/L MC-LR. The comparisons of amoA gene expressions corresponded well with nitrifying kinetics. All concentrations of MC-LR spiking were determined to produce a discernible impact on the AOB nitritation rate by either destroying the bacterial cell or immediately inhibiting the amoA gene expression. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Over the last few decades, the growth of harmful algal blooms (HABs) in many aquatic systems has become a prevalent problem due to increased agricultural runoff, wastewater treatment plant effluents and other nonpoint source discharges with high concen- trations of nutrients getting into lakes (Heisler et al., 2008). While algal and cyanobacterial biomass occur naturally in aquatic eco- systems, cyanobacterial blooms are amplified by anthropogenic activities, such as excess agricultural, point and nonpoint run offs (Paerl et al., 2011; Paerl and Otten, 2013). Cyanotoxins, which are cyanobacterial secondary metabolites, are one of the most potent contaminants found in freshwater ecosystems (Stewart et al., 2008). Human, ecological and microbial health is affected by the toxins produced by cyanobacteria. Microcystin-LR (MC-LR) is mainly a dangerous cyanotoxin, known for accumulating in the liver of humans, livestock, and other animals (Lone et al., 2015). As recent studies demonstrate how climate change correlates to cyanobacterial blooms (Wells et al., 2015; Griffith and Gobler, 2020), cyanotoxin’s ecological impact has become a predominant question in relation to lake water post-bloom conditions (Dalu and Wasserman, 2018). While lake water conditions during algal blooms are toxic to the surrounding plant, animal, and microbial species, long term effects of cyanobacterial blooms are more in- definite. Moreover, cyanotoxin strains have appeared throughout the water column, sediment, marine life, and even tertiary plants in * Corresponding author. E-mail address: ram.goel@utah.edu (R. Goel). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol https://doi.org/10.1016/j.envpol.2020.115283 0269-7491/© 2020 Elsevier Ltd. All rights reserved. Environmental Pollution 266 (2020) 115283