Exploring microbial diversity and function in the degradation of aromatic pollutants from petroleum refineries

<p dir="ltr">Refinery production activities produce large volumes of wastewater and oilcontaminated soil, which contain toxic chemicals that are harmful to human life and natural ecosystems. Effective biotreatment systems for remediation are necessary, where microorganisms play a crucial role. However, studies about microbial communities in the degradation of waste aromatic compounds associated with petroleum refineries are notably scarce. This thesis uses metagenomic analyses, chemical characterisation, and environmental monitoring to explore the relationship between microbial communities and refinery-associated pollutants through four studies. </p><p dir="ltr">The first two studies explore the relationship between microbial communities and wastewater properties within a full-scale petroleum refinery wastewater treatment plant in China. The first study delved into the correlations between microbial taxonomies and wastewater characteristics in the wastewater biotreatment system, identifying dominant organic compounds (cresols and anilines), microbial genera (<i>Thauera </i>and <i>Ignavibacterium</i>), and key environmental factors (pH, nitrite and <i>n</i>-alkanes) that shape community assembly. Expanding on this, the second study focused on genomic insights derived from twenty metagenome-assembled genomes (MAGs) recovered from the aforementioned wastewater biotreatment system, inferring their ecological roles and adaptive strategies, and shedding light on their potential for pollutant degradation and nutrient cycling. <i>Thermaceae </i>sp. is the most metabolically versatile MAG that possesses genes for biomass recycling, catabolism of aliphatic and monoaromatic compounds, and anaerobic respiration of nitrate. To determine the relevance of these findings more broadly, the third study then investigated and compared aromatic hydrocarbon degradation pathways from the Chinese wastewater samples with publicly available metagenomes from similar systems in Argentina and India. From these, putative aromatic degradation genes and their corresponding taxa capable of key degradation steps were identified, and their characteristics were compared across metagenomes. The catechol pathway is among the central pathways commonly utilised by organisms in the Burkholderiales order. Finally, the scope of these investigations was extended in the fourth study, which analysed spatial distributions of organic compounds and microbes in hydrocarbonpolluted soil from a former petroleum refinery in Australia. To achieve this, amplicon surveys and geochemical analyses were used to identify soil taxa associated with specific aromatic pollutants. The hydrocarbon-degrading orders, such as Anaerolineales, Eubacteriales and Spirochaetales, are found to be abundant in heavily hydrocarbon-contaminated soil samples, thus expanding the scope of inquiry to include environmental implications beyond wastewater treatment. </p><p dir="ltr">These findings will contribute to future research that seeks to use microbiomeinformed methods to manipulate petroleum refinery wastewater treatment systems and soil bioremediation processes, allowing more effective strategies for pollutant management to be developed.</p>