Impacts of Microcystis on the Dissemination of the Antibiotic Resistome in Cyanobacterial Blooms

Antimicrobial resistance and harmful cyanobacterial bloom are two health concerns of freshwater ecosystems; a lot of studies have been conducted on these threats. However, few studies have been conducted on the interactions/interplays between these two issues. This study was initiated by the open question of whether the variation in antimicrobial resistance (as described by the resistome) is affected by cyanobacterial bloom, in terms of the shift of the cyanobacterial population. Our results showed that the resistome assembly changed as a net result of joint impacts of environmental factors, mobile gene elements (MGEs), and the bacterial community during the shift of the cyanobacterial population. The abundance of most antibiotic resistance gene (ARG) types declined from aMicrocystis-dominated bloom in the tributary to a multigenus bloom (e.g., Nodosilinea, Cyanobium, Planktothrix, etc.) in the basin. The enrichment of the resistome in the Microcystis-dominated bloom could be attributed to, first, Microcystis being positively correlated to abundant MGEs (e.g., tnpA and plasmid) and subsequently increasing the abundance of the MGE-mediated resistome and, second, Microcystis facilitating the propagation of ARG carriers (e.g., Burkholderiales, Aeromonadales, Sphingomonadales, and Enterobacteriaceae), which are widely reported to exist in the epibiont community of Microcystis. This study suggests a role of Microcystis in resistome dissemination within cyanobacterial blooms. Hence, synergetic pollution control of both Microcystis blooms and antimicrobial resistance is necessary.