Characterization of selected actinomycetes degrading polyaromatic hydrocarbons in liquid culture and spiked soil

Summary Five strains of the Rhodococcus and Gordonia genera were evaluated for their potential use in bioremediation of polycyclic aromatic hydrocarbons (PAH) with or without another substrate (co-substrate). Their ability to produce biosurfactants or to degrade phenanthrene when growing on glucose, hexadecane and rapeseed oil was tested in liquid medium at 30 °C. All strains showed biosurfactant activity. The highest reduction in surface tension was recorded in whole cultures of Rhodococcus sp. DSM 44126 (23.1%) and R. erythropolis DSM 1069 (21.1%) grown on hexadecane and Gordonia sp. APB (20.4%) and R. erythropolis TA57 (18.2%) grown on rapeseed oil. Cultures of Gordonia sp. APB and G. rubripertincta formed emulsions when grown on rapeseed oil. After 14 days of incubation, Rhodococcus sp. DSM 44126 degraded phenanthrene (initial concentration 100 μg ml⁻¹) as sole carbon source (79.4%) and in the presence of hexadecane (80.6%), rapeseed oil (96.8%) and glucose (below the limit of detection). The other strains degraded less than 20%, and then with a co-substrate only. Rhodococcus sp. DSM 44126 was selected and its performance evaluated in soil spiked with a mixture of PAH (200 mg kg⁻¹). The effect of the addition of 0, 0.1 and 1% rapeseed oil as co-substrate was also tested. Inoculation enhanced the degradation of phenanthrene (55.7% and 95.2% with 0.1% oil and without oil respectively) and of anthracene (29.2% with 0.1% oil). Approximately 96% of anthracene and 62% of benzo(a)pyrene disappeared from the soil (inoculated and control) after 14 days and anthraquinone was detected as a metabolite. Rhodococcus sp. DSM 44126 was identified as Rhodococcus wratislaviensis by 16S rRNA sequencing and was able to degrade anthracene as sole carbon source in liquid culture.