Enhancing nitrogen modification in the rhizosphere to alleviate ciprofloxacin and antibiotic-resistant bacteria accumulation in lettuce

Abstract

Investigating methods to minimize the absorption and accumulation of antibiotics and antibiotic-resistant bacteria (ARB) by crops is crucial for mitigating associated health risks. While nitrogen (N) management has proven effective in reducing plant uptake of pollutants, its potential to curb ARB accumulation remains underexplored. This study examined how two N addition methods—graphitic carbon nitride (g-C₃N₄) and nitrate nitrogen (NO₃⁻-N)—on the accumulation of ciprofloxacin (CIP) and ARB in lettuce through pot experiments. Additionally, we analyzed shifts in the rhizosphere microbial community induced by these nitrogenous compounds. As expected, both g-C₃N₄ and NO₃⁻-N reduced CIP accumulation and the relative abundance of ARB in both lettuce tissues and the rhizosphere. g-C₃N₄ showed stronger suppression of ARB in plants than NO₃⁻-N, due to its low cytotoxicity and enhanced photoactivity. Specifically, g-C₃N₄ decreased the proportion of ARB from 23 % to 7 % (p < 0.0001), while NO₃⁻-N reduced it from 22.8 % to 16.7 %. The shared inhibitory effects of both nitrogenous compounds may stem from nitric oxide production via denitrification pathways, a process further supported by the ability of g-C₃N₄ to elevate soil NO₃⁻-N levels. Furthermore, both N treatments altered the rhizosphere bacterial community, reducing network complexity and recruiting distinct microbial populations. Phenotypic predictions corroborated the deactivation of ARB by these nitrogenous compounds. These findings underscore the promise of g-C₃N₄ as a nanoscale N fertilizer for mitigating soil-borne risks posed by CIP and resistant bacteria, offering a sustainable strategy for safer agricultural practices.