The effect of bioaugmentation of petroleum-contaminated soil with Rhodococcus erythropolis strains on removal of petroleum from soil.

The aim of the study was to assess the impact of inoculation of petroleum-contaminated soil with the hydrocarbon-degrading bacterial strains Rhodococcus erythropolis CD 130 and CD 167 or their consortium on the removal of hydrocarbons from the soil. Additionally, changes in the activity and structure of soil autochthonous bacterial communities were studied. At the end of the experiment, the fastest hydrocarbon removal was seen in the soil treated with the CD 167 strain (38.40%) and was statistically higher compared to the removal of total petroleum hydrocarbons (TPH) observed in soils inoculated with strain CD 130 (29.8%) or bacterial consortium CD 130 + CD 167 (29.72%). The rifampicin-resistant CD 130 and CD 167 strains, introduced as single strains or a consortium, survived in the soil for 42 days. The introduction of gram-positive strains of R. erythropolis primarily caused an increase in the biomass of branched phospholipid fatty acids (PLFAs), characteristic for gram-positive bacteria. Nevertheless, changes in the concentrations of gram-positive and gram-negative PLFA markers were periodic, and at the end of the experiment, significant changes were observed only in the case of the soil bioaugmented with the CD 167 strain. After the bioaugmentation, higher values of substrate-induced respiration (SIR) were observed in all the inoculated soils compared to the non-inoculated control. Nonetheless, after 91 days of incubation, a significant decrease in soil respiration was observed in the soil treated with single CD 130 or CD 167 strains or with their consortium. The number of transcripts of the CYP153 gene obtained on days 91 and 182 reflected the results of the hydrocarbon loss. The level of expression of the alkH gene in experimental soil was estimated and found to be higher than the level of expression of the CYP153 gene but did not coincide with the loss of hydrocarbons. The introduction of strains CD 130, CD 167, or CD 130 + CD 167 caused temporary changes in the composition of the soil autochthonous bacterial community, but it seems that these changes were needed for the enhanced removal of hydrocarbons from this soil.