Microbiomes in Ground Water and Alternative Irrigation Water, and Spinach Microbiomes Impacted by Irrigation with Different Types of Water

Irrigation water, particularly if applied overhead, could be an important source of bacterial contamination to fresh produce. The colonization, survival, and proliferation of exogenous bacterial pathogens can be strongly influenced by the produce microbiota. In this study, spinach grown in an organic field was irrigated with ground water and potential alternative irrigation water including reclaimed wastewater, and urban runoff water, over a period of 2 weeks. Water and spinach samples were collected before and after irrigation for bacterial plate count, qPCR, and community profiling using 16S rDNA high-throughput sequencing analyses. The average bacterial population densities on spinach (6.50 +/- 0.04 log CFU/g, 7.40 +/- 0.10 log 16S copies/g) were significantly higher than those in irrigation water (3.61 +/- 0.12 log CFU/ml, 4.94 +/- 0.13 log 16S copies/ml). The composition and relative abundance of spinach microbiomes varied with different types of irrigation waters; however, the most abundant microbial taxa on spinach were not significantly affected by the irrigation with different types of water. Shigella, Salmonella, Listeria, Campytobacter spp., and pathogenic Escherichia coli were not detected in this study. This study provides information on the microbial ecology of diverse bacterial communities on spinach surface after irrigation by different types of water, which can benefit future studies on the interaction of microbes on produce, and the prevention of foodborne pathogens and plant disease.