Exploring diversity patterns and driving mechanisms of the antibiotic resistome and microbiome in saline groundwater

Saline groundwater is witnessed globally, where various factors can exert complex selective pressure on anti-biotic resistance genes (ARGs) (i.e., the resistome). However, the comprehensive profile of the antibiotic resis-tome and its determining factors in saline groundwater is poorly understood. This study comparatively investigated the dynamics of biotic (i.e., microbiota and mobile genetic elements) and abiotic (i.e., water pa-rameters and antibiotics) factors over salinity gradients and further explored their roles in shaping the saline groundwater resistome. Overall, the resistome harbored 166 ARGs conferring resistance to 16 classes of anti-biotics, with an abundance of 0.002-0.306 copies/cell, showing significant variation. The microbiota beta-diversity directly influenced resistome abundance, whereas antibiotics (mainly sulfonamides) and the mobilome directly affected resistome composition. Environmental variables, such as organic carbon, high sulfate-dominated salinity, and metals (e.g., cobalt, potassium, and lithium), indirectly affected the resistome by acting on the microbiota and mobilome. Moreover, inter-correlations of the resistome with mobilome and microbiota weak-ened in groundwater with high salinity, indicating lower horizontal gene transfer potential of the resistome in high-salinity groundwater. The major hosts and mobility potentials of ARGs in the groundwater resistome changed across the salinity gradients. These findings offer vital insights into the management of antimicrobials in saline groundwater.