Native bacteria isolated from weathered petroleum oil-contaminated soils in Tabasco, Mexico, accelerate the degradation petroleum hydrocarbons in saline soil microcosms

Abstract

Bioremediation is an environmentally sound and cost-effective strategy to restore soils contaminated with petroleum oil. In this study, native bio-surfactant-producing bacteria able to use polycyclic aromatic hydrocarbons (PAHs: anthracene [ANT] or phenanthrene [PHE]) as their sole carbon source were isolated from soil contaminated with weathered petroleum oil (WPO) collected near “La Venta” gas processing complex, in Tabasco, Mexico. Bacteria able to grow in 200 ppm of ANT or PHE and having high bio-surfactant activity were selected. Included were bacteria identified as Sphingobium sp., Bosea sp., Pseudomonas sp., Rhodococcus sp. and Phenylobacterium sp. Different consortia of these bacteria ± bio-stimulation with glucose, ammonium nitrate, or both, were examined for their capacity to degrade either WPO or fresh crude petroleum oil (FCPO) in soil microcosms. No efficient short-term (24 days) degradation of WPO using bio-augmentation and bio-stimulation strategies was possible using two bacterial consortia conformed by combinations of these bacterial isolates. Best results were obtained with a consortium composed of Pseudomonas cloritidismutans and Rhodococcus qingshengii, identified by 16S rRNA sequencing, which led to an 86% reduction of FCPO contaminants in soil microcosms, 90 days after treatment. However, the bioremediation efficiency of this consortium was significantly reduced by moderate salinity levels in the soil. Although promising, these results highlight the adverse effect that weathering and/or salinity may have on the remediation of petroleum oil-contaminated soils.