Assessment of Biodegradation Efficiency of Polychlorinated Biphenyls (PCBs) and Petroleum Hydrocarbons (TPH) in Soil Using Three Individual Bacterial Strains and Their Mixed Culture

Abstract

Biodegradation is one of the most effective and profitable methods for the elimination of toxic polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons (TPH) from the environment. In this study, aerobic degradation of the mentioned pollutants by bacterial strains Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN129, and Rhodococcus sp. IN306 and mixed culture M1 developed based on those strains at 1:1:1 ratio was analyzed. The effectiveness of individual strains and of the mixed culture was assessed based on carried out respirometric tests and chromatographic analyses. The Rhodococcus sp. IN306 turned out most effective in terms of 18 PCB congeners biodegradation (54.4%). The biodegradation index was decreasing with an increasing number of chlorine atoms in a molecule. Instead, the Mycolicobacterium frederiksbergense IN53 was the best TPH degrader (37.2%). In a sterile soil, contaminated with PCBs and TPH, the highest biodegradation effectiveness was obtained using inoculation with mixed culture M1, which allowed to reduce both the PCBs (51.8%) and TPH (34.6%) content. The PCBs and TPH biodegradation capacity of the defined mixed culture M1 was verified ex-situ with prism method in a non-sterile soil polluted with aged petroleum hydrocarbons (TPH) and spent transformer oil (PCBs). After inoculation with mixed culture M1, the PCBs were reduced during 6 months by 84.5% and TPH by 70.8% as well as soil toxicity was decreased.

Keywords: bacteria; biodegradation; inoculation; polychlorinated biphenyls (PCBs); total petroleum hydrocarbons (TPH); toxicological tests.

Figure 1

Phylogenetic consensus tree of the stains IN129, IN53 and IN306 with closely related sequences from the NCBI GenBank database. GenBank accession numbers are shown in the Figure. The scale bar corresponds to 10% estimated sequence divergence.

Figure 2

Oxygen consumption by microorganisms Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN129, Rhodococcus sp. IN306 and mixed culture M1 to degrade (a) PCBs (sterile Soil A contaminated PCB), (b) TPH (sterile Soil B contaminated TPH), and (c) PCBs and TPH (sterile Soil C contaminated PCB and TPH) in the biodegradation process. Control-sterile uncontaminated “pure” soil inoculated with bacterial strains and mixed culture.

Figure 3

Residual PCB congeners content in sterile Soil A contaminated with PCBs inoculated by Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN129, Rhodococcus sp. IN306 and mixed culture M1 after a 30-day biodegradation process, (repetition number n = 8–10, p < 0.05). Control-non-inoculated Soil A.

Figure 4

Residual n-alkanes content in sterile Soil B contaminated with TPH inoculated by Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN129, Rhodococcus sp. IN306 and mixed culture M1 after a 30-day biodegradation process, (repetition number n = 8–10, p < 0.05). Control non-inoculated Soil B.

Figure 5

Comparison of biodegradation (%) in sterile Soil C contaminated with both PCBs and TPH after inoculation with Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN129, Rhodococcus sp. IN306, and mixed culture M1: (a) polychlorinated biphenyls; (b) petroleum hydrocarbons (repetition number n = 8–10, p < 0.05).

Figure 6

Residual content of (a) PCB congeners and (b) n-alkanes in non-sterile soil contaminated with both PCBs and petroleum hydrocarbons (Soil D) after 2 (Soil D2), 4 (Soils D4) and 6 (Soil D6) months of inoculation with mixed culture M1 (ex-situ prism method), (repetition number n = 7–10, p < 0.05). Control non-inoculated Soil D.

Figure 7

Comparison of content reduction (a) in PCB-209 normalized PCBs, TriCB, TetraCBs, PentaCBs, HexaCBs, and HeptaCBs (b) in hopane-normalized TPH, ΣnC₁₀–nC₂₂, and ΣnC₂₃–nC₄₀ during inoculation of non-sterile soil D with mixed culture M1 (ex-situ prism method). (repetition number n = 7–10, p < 0.05).

Figure 8

Comparison of toxicity test results expressed in toxicity units (TU) from non-sterile soil during inoculation with mixed culture M1 (ex-situ prism method) (n = 3, p < 0.05): Soil D—raw soil; Soil D3—soil after 3 months; Soil D6—soil after 6 months.

Figure 9

Influence of PCBs and TPH concentration on revertants number (n = 3, p < 0.05): (a) raw soil (Soil D); (b) soil after 3-month biodegradation (Soil D3); (c) soil after 6-month biodegradation (Soil D6); fold increase over the baseline (mutagenicity index).