Assessment of Phenol Detoxification by Rhodococcus aetherivorans UСM Ac-602 Using the Phytotesting Method

Abstract

Monoaromatic compounds are related to widespread pollutants of soil and groundwater. Among them phenol is one of the most toxic and carcinogenic compounds. Therefore biodestruction of phenol is of much importance for environment protection. The use of metabolic potential of microorganisms for depolluting environment is a safe and economical alternative to widely used physicochemical methods. Aim. To assess efficacy of phenol detoxification with strain Rhodococcus aetherivorans UСM Ac-602 using the phytotesting method. Methods. Bacteria were cultivated in liquid mineral medium with initial concentration of phenol 500, 750 and 1000 mg/L as a single source of carbon and energy. Cultivation time was 24 h, 48 h and 72 h respectively. Phytotoxicity was determined in express-test with use of seeds of spring wheat variety “Pecheryanka” (Triticum aestivum L.). Plant seeds were incubated by temperature 20±2°C during 7 days in Petri dishes with filter paper treated with respective phenol aqueous solutions or post-fermentative cultural fluids (PFCFs). PFCFs were obtained after cultivation of strain in growth medium with same concentration of phenol. Morphometric parameters of wheat were assessed against control plants cultivated on distilled water. Comparative analysis of samples toxicity and toxicity class determination was performed according to Kabirov method by calculation of index of test factor toxicity (ITF). Results. Phenol aqueous solutions and PFCFs were much different in effect on wheat. Phenol solutions 500 and 700 mg/L have shown significant inhibitory effect on all initial growth parameters of test plants. The weakest growth inhibition was induced by phenol concentration of 500 mg/L which caused decrease in number of germinated seeds by 59.6%, shoot length – by 59.7%, root length – by 84.5%, sprout dry weight – by 35.0%. In the presence of phenol concentration of 750 mg/L these indicators increased by 7−30%; roots of test plants were the most sensitive to effect of phenol. Phenol concentration of 1000 mg/L caused total seed mortality. Unlike phenol aqueous solutions PFCFs have shown insignificant effect on all morphometric indicators of plants compared to control. Similar effects on plants were observed in the presence of PFCFs obtained from cultivation of strain R. aetherivorans UСM Ac-602 in the growth medium with initial concentrations of phenol of 500 and 750 mg/L. Under the influence of these PFCFs, the number of germinated seeds decreased on average by 15.8%, root length decreased by 19.8%, at the same time shoot length and their dry weight increased by 17.8% and 7.2% respectively. More negative effect on wheat was shown by PFCF obtained after strain cultivation on medium with phenol concentration 1000 mg/L. It caused reduction in number of germinated seeds by 18.0 %, shoot length – by 25.3%, root length – by 29.0%, sprout dry weight – by 7.2%. For phenol aqueous solutions ITFs had much lower values 0–0.40 than for PFCFs (0.71–1.0). Conclusions. Based on data obtained in this research it was concluded that strain R. aetherivorans UCM Ac-602 performs active detoxification of high-concentrated phenol-containing media. Analysis of calculation results for ITF medium values (ITFm) had shown that under the influence of studied strain there was a decrease in toxicity of phenol solutions (500, 750 and 1000 mg/L). According to Kabirov toxicity scale it was assessed that toxicity of phenol solutions with initial values of classes II (high) and I (very high) was decreased to IV (low) and V (normal level). Our results demonstrate ecological safety of the end products of phenol destruction with strain R. aetherivorans UCM AC-602 and prospects of its use in biotechnologies for environment detoxification from phenol pollutions.