Facilitation of conjugative DNA transfer in zooplankton: Insights from Moina macrocopa and Escherichia coli

<h2>Abstract</h2> Zooplankton are vital to aquatic ecosystems and the aquaculture industry. The microbiome within zooplankton plays a crucial role in their growth, fecundity, and stress tolerance. Conjugative DNA transfer can alter the microbiome population, driving microbial evolution, spreading antibiotic resistance, and serving as a tool for microbiome modulation. A previous study found that antibiotic resistance genes can be conjugatively transferred between <i>Enterococcus</i> bacteria in the freshwater zooplankton <i>Daphnia</i>. However, it is unclear whether this phenomenon occurs in other zooplankton species and bacteria, and to what extent zooplankton facilitate conjugative transfer. In this study, we investigated the conjugative transfer of a plasmid belonging to the IncP incompatibility group within the zooplankton <i>Moina macrocopa</i>, a species relevant to aquaculture. We used colony counting and flow cytometry to detect conjugative transfer. Our results indicate that the presence of <i>M. macrocopa</i> increases conjugation efficiency between <i>Escherichia coli</i> by at least five orders of magnitude. <i>In situ</i> conjugative transfer in live <i>M.macrocopa</i> from <i>E. coli</i> to native <i>M. macrocopa</i>-associated microbes, predominantly <i>Flavobacterium</i> and <i>Limnohabitans</i>, was not detected. Following incubation of <i>M. macrocopa</i> carcasses on nutrient-rich agar, <i>Aeromonas</i> became a dominant genus. In this environment, <i>ex situ</i> conjugation from <i>E. coli</i> to <i>M. macrocopa-</i>associated microbes was observed. We isolated transconjugants from the genera <i>Aeromonas</i> and <i>Vogesella</i>, which were able to efficiently transfer the plasmid back to <i>E. coli</i>. These findings have significant implications for understanding the impact of conjugative transfer and the spread of antibiotic resistance in aquatic environments.