Биологические науки/ 6. Микробиология

Khizhnyak S.V., Muchkina E.Y.

Krasnoyarsk State Agrarian University

Changes in the Eisenia foetida digestive tract microbiota after their trophic adaptation to polyethylene

At present time polyethylene is one of the most abundant solid pollutants. According to estimations given by different authors, annually from 16 to 57 million tons of polyethylene are being accumulated in the environment (Shristi Kumar et al., 2007, Sangale et al., 2012).

It was demonstrated that some invertebrates are able to utilize polyethylene, and key role in this process belongs to the bacteria of their digestive tract (Song et al., 2011). The red warms Eisenia foetida Savigny (1826) are using for bioremediation of soils contaminated with wide range of pollutants including oil and heavy metals (Schaefer, Juliane, 2007; Pattnaik, Reddy, 2011), but information on E. foetida application for polyethylene biodegradation is very poor.

It is known that one of the indicators of E. foetida trophic adaptation to substrate is changes in their digestive tract microbiota (Yakushev, Byzov, 2008). The present research is devoted to estimation of changes in bacterial complex in digestive tract of E. foetida cultivated in the soil artificially polluted with polyethylene. Granulated high pressure (low density) polyethylene with granules size of 50-100 µm was used in the experiments (Fig. 1).

Polyethylene was added to the black soil in the dozes of 1.0 and 2.0 g per 1 kg of soil. Worms were incubated in polyethylene polluted and non-polluted soil for 15 days. After incubation the coprolites were collected (1 g of fresh weight per each variant of experiment) and were microbiologically analyzed using PD culture media (peptone – 9.0 g/L, casein hydrolysate – 8.0 g/L, yeast extract – 3.0 g/L, NaCl – 5.0 g/L, Na₂HPO₄ – 2.0 g/L, agar – 20.0 g/L, pH=7,0..7,2).

Fig. 1 – Granulated high pressure polyethylene used in the experiment

After incubation of worms in soil contaminated with 1.0 g/kg polyethylene only insignificant 3% increase of total number of cultivated bacteria in coprolites compared to control was observed. At the same time incubation in soil contaminated with 1.0 g/kg polyethylene statistically significant (p=0.01) increase of cultivated bacteria number of 45% in comparison with control variant was detected (Fig. 2).

Fig. 2 – Numbers of bacteria in coprolites in different variants of experiment

The Discriminant Analyses of the complex of cultural and morphological characteristics of predominated bacterial strains demonstrated that bacterial complex in coprolites of worms cultivated in soil contaminated with 2 g/kg polyethylene was statistically significantly (p<0.01) different from that of worms cultivated in non-contaminated soil.

Observed quantitative and qualitative changes in the bacterial biota in E. foetida digestive tract after their cultivation in the soil contaminated with 2 g/kg polyethylene demonstrates that during the experiment worms consumed and utilized polyethylene and so may be of interest as a biological agent for remediation of polyethylene-polluted soils. An absence of significant changes in digestive tract bacterial biota in the experiment with 1 g/kg of polyethylene may be explained via assumption that for the moment of microbiological analyses all the polyethylene was already utilized and the digestive returned to its normal state.

References:

Yakushev A.V., Byzov B.A. Microbiological characterization of vermicomposts by the method of multisubstrate testing // Eurasian Soil Science. 2008. V. 41. № 11. pp. 1221-1227.

Pattnaik S., Reddy M.V. Heavy metals remediation from urban wastes using three species of earthworm (Eudrilus eugeniae, Eisenia fetida and Perionyx excavatus) // Journal of Environmental Chemistry and Ecotoxicology, 2011, Vol. 3(14), pp. 345-356

Sangale M.K., Shahnawaz M. and Ade A.B. A Review on Biodegradation of Polythene: The Microbial Approach // J Bioremed Biodeg, 2012, 3:10 http://dx.doi.org/10.4172/2155-6199.1000164

Schaefer, M., Juliane, F. The influence of earthworms and organic additives on the biodegradation of oil contaminated soil //Applied Soil Ecology, 2007, Volume 36, Issue 1, Pages 53–62

Shristi Kumar, K., Hatha, A.A.M. and Christi, K.S. Diversity and effectiveness of tropical mangrove soil microflora on the degradation of polythene carry bags // Int. J. Trop. Biol., 2007, 55, pp. 777-786

Song Y., Yang J., Pan H., Li J., Zhu J., Deng X., Khizhnyak S.V., Gurevich Y.L. Isolation and Identification of a Low Density Polyethylene Degradable Bacterium // Advanced Materials Research: Progress in Environmental Science and Engineering, 2011, pp. 172-178