Investigation of Cyanobacteria-Hosted Antibiotic Resistance in Drinking Water Sources from a Public Health Perspective

Abstract

Cyanobacterial blooms are intensifying worldwide due to eutrophication and climate change. While traditionally, the focus has been on cyanotoxins, recent studies suggest a potential link between cyanobacteria and antibiotic resistance (AR), including hosting AR genes (ARGs) or promoting gene transfer. However, the role of cyanobacteria as ARG hosts and their contribution to environmental AR in drinking water sources remains largely unexplored. In this study, we examined cyanobacteria as ARG hosts within the broader microbiome context.  Samples of drinking water sources were collected from Lake Erie and Grand Lake St. Marys (GLSM) between May and October 2022, both sites afflicted historically by blooms. Cyanobacterial genes and ARGs were quantified with DropletDigital™ PCR (ddPCR), while microcystin concentrations were quantified with enzyme-linked immunosorbent assay (ELISA). Shotgun metagenomic sequencing was employed to analyze the microbiome, with ARGs annotated using DeepARG and Resistance Gene Identifier. Although the alpha diversity and composition of the microbial communities were similar at both locations, the ddPCR and sequencing revealed elevated levels of Microcystis in Lake Erie and Planktothrix in GLSM. The ELISA results showed high microcystin concentrations in GLSM. Cyanobacteria were identified as potential hosts for ARGs, including genes such as rpoB2 and arlR. However, upon further examination, these genes are likely annotated on housekeeping genes and are considered false positives spurious hits. In addition, qac and OXA genes were also annotated, consistent with previous findings on NCBI BLAST in Cyanobacteria. Although cyanobacteria do not appear to be significant contributors to the resistome in these contexts, they may confer some antibiotic resistance. This study underscores the importance of continued monitoring of cyanobacteria within the broader microbiome and resistome, especially in drinking water sources with high contamination levels. Understanding the potential interactions and implications of such contaminants for drinking water is crucial for safeguarding public health.

Keywords: Cyanobacterial blooms, resistome, metagenomics, microbiome, Lake Erie, Grand Lake St. Marys