Effects of Exogenous Antibiotic-Resistant Bacteria Exposure on Wheat Seedling Growth and Its Root Endophytes and Rhizosphere Bacterial Communities
To elucidate the effects of exogenous antibiotic-resistant bacteria (ARB) exposure on wheat growth and associated bacterial community assembly, the inhibitory impacts of exogenous ARB on wheat seedling root and shoot length, shifts in root endophytic and rhizosphere bacterial communities, and the horizontal transfer of exogenous antibiotic resistance genes (ARGs) to indigenous endophytic bacteria were investigated using plate culture counting and 16S rRNA high-throughput sequencing. The results showed that exogenous ARB exposure significantly suppressed wheat seedling root and shoot growth, with inhibition rates increasing in an ARB concentration-dependent manner. At an exogenous ARB concentration of 108 CFU/mL, the inhibition rates of seedling root and shoot length reached 68.83% and 36.87%, respectively. During the period of ARB exposure, the relative abundance of Clostridium_sensu_stricto_5 in root endophytic bacteria increased rapidly, becoming the most dominant genus (45.02%) by the end of the exposure period. In contrast, Betaproteobacteriales remained the dominant order in the rhizosphere bacterial community throughout the experiment, with its relative abundance increasing continuously over time. The proportion of ARB-carrying endophytic bacteria initially decreased and then increased during exposure, showing a significant positive correlation with the relative abundances of Clostridium_sensu_stricto_5, Clostridium_sensu_stricto_1, Bacillus, and Paenibacillus (P<0.05). In summary, exogenous ARB exposure significantly inhibits wheat seedling growth and alters the community structure of both root endophytic and rhizosphere bacteria. Sustained ARB exposure leads to the transfer of exogenous ARGs to root endophytes, and Clostridium_sensu_stricto species may act as potential hosts for ARGs in wheat seedling roots.