Changes of endophytic bacterial community and pathogens in pepper (Capsicum annuum L.) as affected by reclaimed water irrigation

The occurrence and distribution of potential pathogens in reclaimed water are severe public health concerns. Therefore, to assess the impact of reclaimed water irrigation on endophytic bacterial communities and potential pathogens, a pot experiment was conducted to compare reclaimed water irrigation with tap water irrigation using pepper as a test crop. In this work, the diversity and community structure of endophytic bacteria were investigated, as well as the potential pathogens in peppers irrigated with full reclaimed water or diluted reclaimed water, using a combined approach of Illumina-MiSeq amplicon sequencing and real-time quantitative PCR. 16S rRNA gene sequence analyses demonstrated that Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes were the dominant bacterial phyla both in root and fruit endophytes. Pseudomonas, Comamonas, and Flavobacterium were the dominant endophytic potential pathogens. Furthermore, some phytopathogens were also identified, including Ralstonia and Erwinia. Additionally, our results showed that the concentrations of Aeromonas hydrophila, Escherichia coli, and Pseudomonas syringae were significantly lower in plant endophytes irrigated with diluted reclaimed water than those of irrigated with undiluted reclaimed water, indicating that mixing reclaimed water and tap water in appropriate proportions may reduce the abundances of potential pathogens in endophytes. In conclusion, this study provides a comprehensive evaluation of bacterial communities in pepper endophytes exposed to reclaimed water irrigation and proposes a potential strategy to decrease human and crop health risks from pathogens in reclaimed water, thereby improving crop safety.