Nwajiobi, Ifeoma Judith2025-10-092025-10-092024-11Nwajiobi, I. J. (2024). Plant-endophytic bacterial interactions in phytoremediation of crude oil polluted soil (Unpublished Doctoral Thesis). Federal University of Technology, Owerri, Nigeria.https://repository.futo.edu.ng/handle/20.500.14562/2221Doctoral thesis on plant-endophytic bacterial interactions. It contains tables and pictures.Endophytes reside within plant hosts asymptomatically, exhibiting continuous metabolic interactions with their hosts. The study investigated the role of plant-bacterial endophytes during phytoremediation of soil polluted with crude oil. Growth performance of Hibiscus cannabinus and Zea mays in remediation of crude oil-polluted soil samples after 90 days was analysed. Physico-chemical parameters and total petroleum hydrocarbon content of crude oilpolluted soils were analysed. Endophytic bacteria within the roots of H. cannabinus and Z. mays were isolated, tested for their bioremediation potentials and plant growth properties. Additionally, the genomic DNA of isolated endophytic bacteria were analysed for the presence of hydrocarbon degradative genes (Alk B genes). The 16s rRNA amplicons of gDNA of endophytic bacteria isolates were sequenced and phylogenetic tree constructed. Results of the physico-chemical parameters show the pH of the polluted soil from Egbema were acidic (4.8 to 6.6) before plant growth. Moisture content and organic carbon had mean ranges of 10.00- 15.00% and 0.86-2.45% respectively. After planting using H. cannabinus, pH values, moisture content and organic carbon increased to a mean range value of 5.4-6.1 and 15.30-27.90% respectively while organic carbon decreased to a mean range value of 0.45-2.12%. The mean pH, moisture content and organic carbon were within the range 5.2-8.4, 5.00-28.10% and 0.24- 1.84% respectively after plant growth using Z. mays, indicating that Z. mays offered greater remediation than H. cannabinus on oil-polluted soil. Growth performance observed during plant growth revealed that 5ml/5kg crude oil-polluted soil had the highest agronomic parameters, offering the highest crude oil remediation (46.01%) recorded using H. cannabinus, while 5kg Egbema-polluted soil without organic amendment showed the least remediation (4.63%). Similarly, 5ml/5kg crude oil-polluted soil showed the highest crude oil remediation (56.05%) while 5kg Egbema-polluted soil without organic amendment showed the least crude oil remediation (11.04%) after plant growth using Z. mays. A total of 57 endophytic bacteria were isolated from the roots of H. cannabinus and Z. mays. Six endophytic bacteria synthesized indole acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC) deaminase and siderophores; 14 isolates synthesized IAA and ACC; 16 isolates synthesized IAA and siderophores while 7 isolates synthesized ACC and siderophores at 10.53%, 24.56%, 28.07% and 12.28% respectively. Hydrocarbon degradation potential of isolated bacterial endophytes showed that all isolates (100%) could metabolize 2% (w/v) C6, C8, C10 and 2% (v/v) diesel as alternate sources of carbon in the absence of glucose. Moreover, genomic DNA of endophytic isolates possessed alkane monoxygenase genes responsible for hydrocarbon degradation in bacteria species. Sequenced 16s rDNA amplicons showed similarity of endophytic bacteria from the study to the genera Proteus and Alcaligenes. This study established the presence of Proteus vulgaris, Proteus mirabilis and Alcaligenes spp as the predominant endophytic bacteria within the roots of the phytoremediation plants H. cannabinus and Z. mays. Additionally, the presence of alkane monooxygenase genes and the ability of endophytic bacteria isolates to grow on diesel oil and n-alkanes served as an indication of the potential application of the isolates in bioremediation activities.enAttribution-NonCommercial-NoDerivatives 4.0 InternationalEndophytic bacteriacrude oil remediationplant growth-promoting propertieshydrocarbon degradative genesproteus sppDoctoral Thesis