Bacterial Consortia Improve Vetiver Zizanioides Mediated Hydrocarbon Degradation and Drive Compartment Specific Bacterial Dynamics in the Rhizosphere and Endosphere

Pollution by petroleum hydrocarbons remains a critical environmental crisis and remediation efforts are shifting towards nature-based solutions such as phytoremediation and the utilization of microbial consortia. The current study assessed the effectiveness of Vetiveria zizanioides (Vetiver grass) and an inoculated bacterial consortium to promote total petroleum hydrocarbon (TPH) remediation and analysed the bacteriome in the rhizosphere and endosphere. The bacterial consortia were made from hydrocarbon-degrading and biosurfactant producing isolates (Bacillus subtilis, Mitsuaria chitosanitabida, Burkholderia pseudomultivorans, and Acinetobacter seifertii) from the rhizosphere of Panicum virgatum growing in natural oil-contaminated soils. In soil microcosm experiments, Vetiver plants inoculated with the bacterial consortium achieved the highest reduction in TPH relative to Controls over the 60-day experimental period. While oil treatment reduced biomass relative to other treatments, Vetiver growth was sustained and improved in the presence of the bacterial consortium. Overall, the treatment with Oil + Consortia + Vetiver had the least (P < 0.05) TPH concentration, followed by the Oil + Consortia, and Oil + Vetiver. At Day 60, the combined Oil + Consortia + Vetiver treatment reduced total petroleum hydrocarbons by 96% relative to the initial day zero. Net biomass change over the 60-day period showed that Vetiver + Consortia had the highest gains (shoot: + 41.6 g; root: + 37.1 g), followed by Vetiver (shoot: + 29.4 g; root: + 28.1 g), Vetiver + Oil + Consortia (shoot: + 24.8 g; root: + 18.5 g), while Vetiver + Oil had the lowest increases (shoot: + 16.8 g; root: + 14.1 g). Bacterial community analysis of both the rhizosphere and endosphere through 16S rRNA amplicon sequencing revealed treatment and compartment specific shifts, with enrichment of hydrocarbon-associated bacterial genera such as Pseudomonas, Bacillus, Burkholderia, and Acinetobacter. Differential abundance analysis showed that Sphingomonas, Hyphomicrobium, Azoarcus, and Oleomonas had significant log fold change increases across treatments, whereas Pseudomonadales, Nitrososphaeraceae, and Porticoccaceae were generally characterized by reduced abundance. Additionally canonical correspondence analysis constrained by TPH revealed distinct genera positioned toward the higher TPH end of the ordination and included Candidatus, Accumulibacter, Simplicispira, Algoriphagus, Sedimentibacter, Azotobacter, Holophaga, Curvibacter, Sulfurisoma, and Micavibrio. Overall, the result of the study overall suggests that a combination of Vetiver and bacterial consortium enhances bioremediation of TPH and highlights the potential role of plant–microbe interactions in supporting nature-based solutions especially in small island states where traditional remediation strategies may not be feasible.