Bioremediation of petroleum-contaminated soils using Streptomyces sp. Hlh1

Purpose

Bioremediation using microorganisms is a promising strategy to remediate soil with petroleum hydrocarbons. Streptomyces sp. Hlh1, an endophytic strain, has previously demonstrated the ability to degrade crude petroleum in liquid culture. To apply this strain at field scale, it is necessary to test its ability to colonize the soil, compete with native microbiota, and remove the petroleum hydrocarbons under unfavorable conditions. Herein, a study was conducted to evaluate the performance of Streptomyces sp. Hlh1 to remove crude petroleum from contaminated sterilized and non-sterilized soils.

Materials and methods

Soils samples, contaminated with 2%, 5%, and 10% of petroleum, were inoculated with Streptomyces sp. Hlh1, and incubated at 30 °C for 4 weeks. At the end of bioremediation assays, the pollutant concentrations were determined by Gas chromatography flame ionization detector and the degradation rates were also calculated. The survival of the strain in the soil was estimated and the toxicity of metabolites was evaluated on Lactuca sativa.

Results and discussion

Streptomyces sp. Hlh1 was able to grow and remove total petroleum hydrocarbons (TPH), n-alkanes, and aromatic hydrocarbons found in soil samples. In sterilized soil samples, Streptomyces sp. Hlh1 removed up to 40% of TPH at an initial concentration of 10%. Whereas, the maximum TPH removal reached was 55% in non-sterilized soil at an initial concentration of 2%. In addition, it was observed that the degradation of aromatic hydrocarbons was more active than n-alkanes. The strain grew well and produced high biomass in contaminated soil. Lettuce seedling was found to be the adequate bioindicator to assess the toxicity of petroleum end products. Streptomyces sp. Hlh1 performed a successful bioremediation, which was confirmed through the phytotoxicity test.

Conclusions

The study shows the first insight of the contribution of free endophytic actinobacterial strain in the bioremediation of petroleum-contaminated soil; therefore, it suggests that Streptomyces sp. Hl1 can be usefully exploited at field scale.

     

Myorelaxant and antispasmodic effects of the aqueous extract of Mitragyna inermis barks on Wistar rat ileum

Mitragyna inermis is used in the Senegal traditional medicine for treating stomach and intestinal disorders. At concentrations of 0.5, 0.75 and 1 mg/ml, the aqueous extract of M. inermis bark (AEMIB) significantly induced a decrease of the ileal basal tonus, respectively, from 37+/-1, 51+/-1 and 75+/-2% (P<0.05; n=5), compared to the baseline values. As well as atropine, AEMIB inhibited submaximal contractions induced by 0.01 mg/ml ACh with IC(50) value of approximately 0.75 mg/ml (n=5). These results show that AEMIB possesses both myorelaxant and antispasmodic actions in the ileum. This may justify the pharmacological basis for the popular use of Mitragyna for the treatment of gastrointestinal disorders.