Microbial communities associated with landfarming amendments during bioremediation of crude oil in Niger Delta soils

Landfarming is a widely utilized process that involves using bacterial biodegradation to remediate contaminated soil resulting from oil spillages. Its effectiveness can be improved using amendments that include fertilizers, biosurfactants, enzymes, and natural sorbents. The effects of these amendments on biodegradation efficiency and the microbial community composition were investigated using 16S rRNA gene amplicon sequencing analyses performed on soil samples collected from a large-scale mesocosm experiment. The results showed that the use of amendments had a profound influence on the microbial community, which decreased with time following application of the amendment. Interestingly, the relationship between observed microbial diversity and biodegradation efficiency changed over time. During the initial phase, a higher biodegradation rate correlated with lower biodiversity indices, while during the later phase this relation reversed, and a higher biodegradation rate correlated with higher biodiversity indices. Two mesocosms types, one with biochar plus rhamnolipids and the other with agricultural lime, both in combination with fertilizer, degraded the oil significantly better than the ‘oil-only control’ with biodegradation improvements of 32.5 % and 25.8 %, respectively. Both combinations of amendments also promoted different adaptive responses of the microbial community with higher abundances of members of the genus Sphingomonas in both cases. •Oil exposure causes successional changes of the soil microbial community.•After oil exposure, time and soil pH are key drivers of the microbial consortia.•The recovery of microbial diversity and soil stability depends on the oil removal.•High abundance of the genus Sphingomonas correlate with oil biodegradation enhance.