Prevalence and distribution of antibiotic-resistant bacteria in the rhizosphere and rhizoplane of Suaeda salsa and Sporobolus alterniflorus grown in a pristine environment

Antibiotic-resistant bacteria (ARB) are believed to have originated from pristine soil environments. However, the prevalence of ARB in the root-associated niches of plants grown in these environments, as well as the distribution patterns of ARB in the rhizosphere and rhizoplane-two critical root-associated niches-remains elusive. In this study, we investigated the prevalence and distribution of ARB in the rhizosphere and rhizoplane of two main plant species, Suaeda salsa and Sporobolus alterniflorus, grown in a pristine environment in Yancheng, China, to address these questions. In total,181 bacterial strains were isolated from the root-associated niches of the two plant species. Strong niche differentiation of the bacterial community between the rhizosphere and rhizoplane was identified by both bacterial isolation- and high-throughput 16S ribosomal RNA gene (rDNA) sequencingbased analyses. In total, 69.06 % of the isolated bacterial strains were classified as ARB, with strains resistant to beta-lactam class antibiotics and polymyxin being predominant. The relative abundance of ARB in the rhizoplane was higher than that in the rhizosphere for both plant species. Furthermore, variations were noted in the prevalence and distribution of ARB in the root-associated niches between the two species. Several pathogenic ARBs, such as Stenotrophomonas maltophilia, were identified among the isolated strains. A representative S. maltophilia strain was sequenced, and several important antibiotic resistance- and pathogenicity-associated genes were identified in its genome. These findings provide novel insights into the prevalence and distribution patterns of ARB in the rhizosphere and rhizoplane of plants grown in pristine environments.