Assessment of the effect of different bioremediation approaches on the soil microbiome of fuel-affected areas

The use of biofuels has grown in the last decades, due to climate and security energy issues and environmental impacts of fossil fuels use. Currently in Brazil, biodiesel is being used in blends with diesel (also called B12) and ethanol in blends with gasoline (also called E27). With increased use of those blends, cases of biofuel pollution in soil, surface and groundwater are expected. Elucidating structure, diversity, species interactions and assembly mechanisms of microbial communities is crucial for understanding the influence of environmental disturbances (i.e., pollution and/or the use of bioremediation treatments). However, little is known about how contamination with biofuel / petrofuel blends alters the soil microbiome. This study aimed to deeply characterize the soil microbiome of four areas intentionally polluted with E10, E25 or B20 and submitted to different bioremediation treatments (i.e., injection of anaerobic electron acceptors, biosparging or bioaugmentation), using 16S rRNA gene amplicon high throughput sequencing. Results indicated that the soil microbiome of biodiesel affected areas is more diverse and complex, likely due to the presence of syntrophic microorganisms, such as Clostridium and methanogenic archaea. It was also observed that in soils with low diversity and richness, the impact of bioremediation treatments on the microbial communities was higher. The network analysis showed that after the application of the bioremediation treatment, hub species appeared and the proportion of generalist taxa (more linked species) increased, suggesting that the treatment contributed to a more connected and dynamic assembly. All abundant keystone taxa are well-known degraders, suggesting that the abundant species are core targets for biostimulation in soil remediation. Overall, these findings extend our knowledge of the soil microbiome response triggered by pollution stress and bioremediation treatments, paving the way for future rationalized and efficient pollutant mitigation strategies.