Comparative High-Throughput Sequencing Analysis of the Bacterial Community Associated with the Rhizosphere of Date Palm (Phoenix dactyllifera L.) Irrigated with Treated Wastewater and Groundwater

Water scarcity is a major agricultural issue in most arid and semi-arid regions of the world. Alternative water supplies, such as the reuse of wastewater for agricultural irrigation, have been introduced. However, little is known about their impact on the soil and rhizosphere microbiomes that receive irrigation. Therefore, this work evaluates the impact of treated wastewater (TWW) irrigation on the soil and rhizosphere bacterial communities of date palms in Al Madinah, Saudi Arabia. In this study, metagenomic DNA from the rhizosphere of the date palm was sequenced using Illumina high-throughput sequencing. According to the observed OTUs, Chao1 richness estimations, and Shannon diversity values, soils from groundwater-irrigated date palms showed higher microbial diversity than did soils from TWW-irrigated date palms. A total of 569 OTUs were generated; most of them (97.3%) were assigned into 15 different phyla, whereas 2.7% were marked as unclassified. DNA sequence analysis of the WWT-irrigated rhizosphere showed that the most abundant phyla were Firmicutes (43.6%), Bacteroidetes (17.3%), Proteobacteria (15.2%), and Actinobacteria (14.6%), representing more than 90.7% of the total community, while the soil of the rhizosphere irrigated with GW was dominated by Actinobacteria (44.1%), Proteobacteria (23.4%), Firmicutes (15.5%), and Gemmatimonadetes (4.9%). The most frequently observed species in the two soils were also different. The dominant species in TWW-irrigated soil was Planococcus plakortidis, which is prevalent in saline and moderately saline habitats and can play an important ecological role. The GW-irrigated rhizosphere exhibited higher levels of biocontrol bacteria, particularly Nocardioides mesophilus. These results provide a comprehensive understanding and insights into the population dynamics and microbiome of date palm rhizosphere. The findings show that the irrigation water quality has a significant impact on the microbiome composition. Identifying the microbial diversity is the first step toward determining the best way to use TWW in irrigation.