Emergence of hydrocarbon-degrading bacteria in crude oil-contaminated soil in a hyperarid ecosystem: Effect of phosphate addition and augmentation with nitrogen-fixing cyanobacteria on oil bioremediation

Hyperarid hot deserts impose limiting conditions for microbial activity, thus delaying crude oil biodegradation resulting from accidental spills. This study examined the emergence of oil-degrading bacterial species in the soil of a hyperarid area in the southern Negev desert, Israel, which was exposed to a major oil spill. Amplicon sequencing of the 16S rRNA gene showed dominance of the phyla Proteobacteria and Actinobacteria in both contaminated and control soils. Significant differences were seen in the abundance of the phylum Firmicutes. Classes Actinobacteria, Gammaproteobacteria and Bacilli dominated the oil-contaminated soil. Bacterial species capable of degrading aromatic and aliphatic oil constituents were isolated from the contaminated soil. Contaminated soil microcosms were amended separately with nitrogen, phosphorus, or nitrogen-fixing cyano-bacteria (NFC) biomass; the highest reduction in total petroleum hydrocarbons was observed in the phosphorus-supplemented soil. The abundance of alkB gene, encoding alkane monooxygenase, increased significantly in the control, NFC and phosphate treatments, but not in the nitrogen treatment. However, nahA abundance (coding for naphthalene dioxygenase) was only considerably increased with the phosphorus amendment. While nitrogen amendment via NFC bioaugmentation is a sustainable and novel biostimulation method, phosphorus amendment significantly accelerates the biodegradation of crude oil under extremely arid conditions.