Assessment of the Responsiveness to Different Stresses of the Microbial Community from Long-Term Hydrocarbon-Contaminated Soils

Soils exposed to long-term contamination with hydrocarbons may present extreme challenges to maintain the biological resilience to the stress. To eluci- date the relationships between the initial event of con- tamination and the responsiveness to the stress, we investigated the extent of the microbial resilience of biological functions from two contaminated soils sam- pled from a petrochemical area (S1, underwent diffuse hydrocarbon contamination, and S2, from a land farm- ing unit where an alkaline petrochemical sludge was treated) after the Cd, saline, and acid stresses. Both contaminated soils were characterized by low organic matter content compared with a pristine soil. Although similar Shannon diversity index and heterotrophic bac- terial count were observed, different bacterial commu- nity structures (PCR-DGGE) and less enzymatic activ- ities characterized the contaminated soils. Particularly, functional diversity determined by Biolog EcoPlatesTM was not detected in S2 soil. Only the S1 soil showed resilience of the enzymatic activities and functional diversity, suggesting the presence of a well-adapted microbial community able to face with the stresses.The S2 was the most disturbed and less responsive soil. However, an increase in the functional diversity was evidenced after acidification, and it is possible to corre- late this responsiveness with the sludge properties treat- ed in the land farming unit. In addition, if the selected stress can reverse the soil condition provoked for the first disturbance, responsiveness could be expected