Dynamics of microbial communities on spinach irrigated by ground water, reclaimed water and roof-harvest 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. The objective of this study is to investigate the dynamics of bacterial community on spinach after irrigation by ground water (Cr), reclaimed-waste water (Wa), and roof-collection water (Rf). Spinach was irrigated with three types of water (Cr, Wa, Rf) in two weeks in a randomized complete block design with 2 replicates (plot) for each treatment. Spinach before and after irrigation and water samples were collected for bacterial plate count, qPCR, and 16S rDNA sequencing survey analyses. The average bacterial population densities on spinach (plate count: 6.50 ± 0.04 log CFU/g; qPCR estimation: 7.40 ± 0.10 log 16S copies/g) were significantly higher than that in tested irrigation water (3.61 ± 0.12 log CFU/ml, 4.94 ± 0.13 log 16S copies/ml). The composition of bacterial communities in Cr changed between the two sampling weeks, while the composition was not significantly shifted in Wa and Rf. The dominant bacterial taxa on spinach were not significantly affected during the two-week irrigation, however, certain bacterial species were transmitted to spinach through irrigation. This study provides knowledge on the microbial ecology of diverse bacterial communites on spinach after irrigation by different types of water, which can benefit further studies on the interaction of microbes on produce, and the prevention of foodborne pathogens and plant disease.

灌溉用水，尤其是采用喷洒方式施用，可能成为新鲜农产品细菌污染的重要来源。外源细菌病原体的定植、存活和增殖可受到农产品微生物群的强烈影响。本研究的目的是探究经地下水（Cr）、再生废水（Wa）和屋顶收集水（Rf）灌溉后菠菜上细菌群落的动态变化。菠菜在两周内采用随机完全区组设计，以每种处理设置两个重复（小区）进行灌溉，灌溉用水包括Cr、Wa和Rf三种类型。收集灌溉前后的菠菜及水样，进行细菌平板计数、qPCR和16S rDNA测序调查分析。菠菜上的平均细菌种群密度（平板计数：6.50 ± 0.04 log CFU/g；qPCR估计：7.40 ± 0.10 log 16S拷贝/g）显著高于所测试的灌溉水（3.61 ± 0.12 log CFU/ml，4.94 ± 0.13 log 16S拷贝/ml）。Cr中细菌群落组成在两次采样周之间发生变化，而Wa和Rf的组成没有发生显著转变。菠菜上的优势细菌类群在两周灌溉期间未受到显著影响，然而，某些细菌物种通过灌溉传播到菠菜上。本研究为不同类型灌溉水灌溉后菠菜上多种细菌群落的微生物生态学提供了知识，这有助于进一步研究微生物在农产品上的相互作用，以及食源病原体和植物病害的预防。