Short-Term Warming Induces Cyanobacterial Blooms and Antibiotic Resistance in a Freshwater Lake as Revealed by Metagenomics Analysis

Abstract

Climate change poses significant risks to freshwater ecosystems, potentially exacerbating harmful cyanobacterial blooms and antibiotic resistance. We investigated these dual threats in Cosseys Reservoir, New Zealand, by simulating short-term warming scenarios and assessing the role of oxidative stress. Microcosms were subjected to Base (22°C), Normal (24°C), and projected Future (27°C) temperatures, with additional treatments including reactive oxygen species (ROS). Metagenomic analysis revealed substantial restructuring of microbial communities under warming conditions. Cyanobacterial abundance increased from 6.11% (initial) to 20.53% at 24°C and 10.66% at 27°C. Notably, ROS addition mimicked the effects of temperature increase on cyanobacterial proliferation. Toxin-producing families, including Microcystaceae and Nostocaceae , proliferated significantly. The microcystin synthesis gene ( mcy ) showed a strong positive association (R² = 0.88) with cyanobacterial abundance. Moreover, cyanobacteria exhibited enhanced nutrient acquisition ( pstS gene, R² = 0.69) and upregulated nitrogen metabolism pathways under warming conditions. Concurrently, we observed a marked increase in antibiotic resistance gene (ARG) abundance with rising temperatures. The relative abundance of multidrug resistance genes was consistently high across all conditions (50.82 % of total ARGs). ROS stress further intensified ARG proliferation, particularly for efflux pump genes ( e.g. , acrB , adeJ , ceoB , emrB , MexK , muxB ). Co-association network analysis identified key antibiotic-resistant bacteria ( e.g. , Streptococcus pneumoniae , Acinetobacter baylyi ) and ARGs ( e.g. , acrB , MexK , rpoB2 , bacA ) central to resistance dissemination under warming conditions. This study demonstrates that even modest temperature increases (2-5°C) can promote both cyanobacterial blooms and antibiotic resistance in freshwater ecosystems over short time scales. The synergistic effects of temperature and oxidative stress underscore the complex challenges posed by climate change to water quality and public health. Highlights: Short-term warming promotes toxic cyanobacteria and antibiotic resistance in freshwater. Harmful cyanobacteria and their metabolic potential increase under warming conditions. Reactive oxygen species mimic and exacerbate temperature effects. Oxidative stress response genes strongly correlate with ARG abundance. Co-association networks identify key host pathogen central to resistance spread.