While the value of bioremediation for the cleanup of hydrocarbon (HC) impacted environments is widely acknowledged, the role of enrichment substrate for HC-degrading microorganisms is often overlooked. The feasibility of “pre-conditioning” HC-degrading microorganisms in order to enhance their degradative potential was investigated by selective enrichment of the HC-degraders on a range of chemicals that were expected to induce the enzymatic machinery responsible for the degradation of HCs. We hypothesised that enrichment medium determines the biodegradative performance of the microbial cultures. A range of degradation experiments were carried out using Psuedumonas putida F1 and its bioluminescent version, P. putida TVA8 and mixed cultures of HC-degraders isolated from a commercial inoculum constructed to provide insight into the interactions at the community level.
Each experiment consisted of three consecutive stages: a growth stages, a conditioning step where each bacterial isolate was transferred to media with different carbon (C) sources and a degradation experiment. Similarly, the effect of enrichment substrate on HC degradation profile and respiration was investigated using three HC degraders, individually and in all possible combinations. Changes in relative species abundance in the mixed cultures was also quantified and linked to HC degradation, using PCR-DGGE band intensity analysis.
When toluene was the sole C source in the degradation stage, results from the measured parameters including OD, CFU, biomass-C, CO2-C, toluene concentration and bioluminescence indicated that toluene-conditioned treatment resulted in significantly (P≤ 0.05) higher activity for both P. putida F1 and P.putida TVA8. Variation in enrichment substrate provoked significant differences (P≤ 0.05) in C mass balance and may increase the assimilative and toluene degradative capabilities. Post-incubation DGGE band intensity analysis for populations of most mixed cultures indicated significant (P≤ 0.05) changes in the percentage species abundance. The relative species abundance within culture combinations was significantly affected by both the isolate and the conditioning substrate.