ROOT AND SOIL MICROBIOME RESPONSE TO TREATED WASTEWATER IRRIGATION

Treated Wastewater (TWW) irrigation is becoming a major and essential component of agricultural practice in increasing parts of the world. Despite the improvement in its quality, TWW may still cause unexplained undesirable effects on crops. This may be attributed, among others, to TWW effects on the roots and its microbiome, as they are the first to encounter the TWW effects.

In the current study, we examined the effects of TWW irrigation on rhizosphere and root surface (rhizoplane) microbial community composition (based on 16S rRNA amplicon sequencing) of tomato and lettuce plants grown in two different soil types.

Both TWW irrigation and the host plant affected the rhizoplane bacterial communities, while the rhizosphere bacterial communities were mainly determined by the soil type and TWW irrigation. In both habitats, TWW irrigation was as significant as the other factors shaping the bacterial community. More than 15% of the bacterial OTUs changed significantly as a result of the TWW irrigation, but the change was habitat specific. For tomato rhizoplane, the most prominent change was dramatic increase in relative abundance of the bacterial order Pseudomonadales.

Several Pseudomonas sp. strains isolated from root surface of TWW irrigated tomato, and identified as P.mendocina and P.indica. Those strains were 99% similar (based on full 16S rRNA sequence) to indicator species found mostly on TWW irrigated roots (based on the amplicon sequencing). Those bacteria will be further characterized to examine their effect on plant irrigated with TWW.

As the roots and their microbiome are exposed to the same environmental condition, it is hypothesized that understanding the plant root microbiome response to TWW will contribute to the understanding of its specific impacts.