Effects of Irrigation on Alkane Biodegradation of Oil-Contaminated Desert Soils

Biodegradation in oil-contaminated desert soils can be limited by the lack of nutrients and/or water. We investigated the effect of irrigation, using nutrient-free and -amended distilled water, sewage water and seawater on alkane degradation rates in an oil-contaminated desert soil. Nutrient-amended soils exhibited the highest alkane degradation rate (74%). MiSeq sequencing of nutrient-amended soils revealed the dominance of Gammaproteobacteria, with most sequences belonging to Sphingomonas. From this soil, 50% of the isolated alkane-degrading strains belonged to Pseudomonas. Sewage-treated soils showed the most prominent bacterial community shift in favor of Firmicutes. Bacterial diversity suggested the introduction of microorganisms from sewage water and the development of anoxic conditions. Seawater-treated soils exhibited the lowest degradation rates (11%), owing to the increase in soil salinity, although known alkane-degrading bacteria like Alcanivorax and Sphingomonas were detectable. We conclude that not mere irrigation but irrigation with nutrients significantly enhances biodegradation rates in oil-contaminated desert soils.