Antibiotic resistance gene profile in aerobic granular reactor under antibiotic stress: Can eukaryotic microalgae act as inhibiting factor?

Antibiotic resistance gene (ARG) pollution is critical environmental problem, and horizontal gene transfer acts as a driving evolutionary force. In theory, due to the phylogenetic distance between eukaryotes and prokaryotes, eukaryotic microalgae can be a natural barrier that plays a negative role in ARG transfer among the symbiotic bacteria to decrease ARG abundance in sludge during wastewater treatment. However, this hypothesis is far from proven and needs to be tested experimentally, so this study investigated the influence of eukaryote microalgae (Scenedesmus) on the ARG profile of symbiotic bacteria based on aerobic granular reactor. The results indicated that Scenedesmus symbiosis could affect ARG diversity of bacteria, and the detected numbers of ARG in aerobic granular sludge (AG) group and algae-bacteria granular consortia (AAG) group were 45-53 and 44-47, respectively. In terms of relative abundance, after target microalgae symbiosis, the total abundance of ARGs significantly decreased from 1.17 x 10 degrees, 2.69 x 10 degrees and 1.36 x 10(-1) to 6.53 x 10(-1), 9.64 x 10(-1) and 1.04 x 10(-1) in the systems with the addition of streptomycin, azithromycin and vancomycin, respectively (P < 0.05), yet there was no significant difference between AG and AAG under the stress of ampicillin, sulfamethazine and tetracycline (P > 0.05). Redundancy analysis showed that the eukaryotic microalgae were significant factor explaining the change in ARG relative abundance (P < 0.05), which contributed 15.3% of ARG variation. Furthermore, the results show that, except for the tetracycline treatment system, the total relative abundances of MGEs in the AAG under the stress of the other five antibiotics were 3.54 x 10(-2)-7.13 x 10(-1), which were all significantly lower than those in the AG (8.38 x 10(-2)-1.59 x 10 degrees). There was a more significant positive correlation relationship between ARGs and mobile genetic elements (MGEs) than that between ARGs and dominated bacteria.

Automated summary

This study investigates the influence of eukaryote microalgae on the antibiotic resistance gene (ARG) profile of symbiotic bacteria. The results show that the symbiosis of microalgae can decrease the abundance of ARGs in bacteria, and there is a strong correlation between ARGs and mobile genetic elements (MGEs).