Pyrene degradation by Chlorella sp. MM3 in liquid medium and soil slurry: Possible role of dihydrolipoamide acetyltransferase in pyrene biodegradation

Abstract

Microalgae inhabiting the real contaminated sites are capable of degrading organic pollutants. In the present study, the potential of a microalga, Chlorella ssp. MM3, a soil isolate from a former cattle dip site, was assessed in degrading pyrene both in aqueous medium and soil slurry. Strain MM3 can grow on pyrene in culture medium at concentrations as high as 250μM. When grown in presence of 50μM pyrene, the cell density increased from 1.1×105cellsmL−1 to 16.45×105cellsmL−1 within 7days. With an initial cell density of 3×107cellsmL−1, nearly 70% of 50μM pyrene was degraded after 7days of incubation. When compared with Triton X-100, Tween 80 was a better non-ionic surfactant for pyrene biodegradation. Nearly 20% increase in degradation of pyrene was observed with the use of 0.005% Tween 80. Differential protein expression in pyrene-grown cells of the microalga resulted in distinct accumulation of dihydrolipoamide acetyltransferase (or dihydrolipoyl transacetylase), one of the three components of pyruvate dehydrogenase complex, indicating a possible role of this enzyme in microalgal degradation of pyrene. The microalgal cells immobilized in calcium alginate completely degraded 50μM of pyrene within 10days in nonsterile soil slurry treated with 0.005% Tween 80. Our results clearly indicate that the strain MM3 has a great potential for its use in remediating soils contaminated with pyrene.