Use of Styrene as Sole Carbon Source by the Fungus Exophiala oligosperma: Optimization and Modeling of Biodegradation, Pathway Elucidation, and Cell Membrane Composition

Abstract

Biodegradation of styrene by Exophiala sp. was tested at different initial concentrations (19.3–170.6 mg l−1), pH (2.8–8.7), and temperatures (19.8–45.1 °C), for 120 h according to a 23 full-factorial central composite design. The specific growth rate (SGR, per hour) and specific styrene utilization rate (SUR, milligrams of styrene per milligram of biomass per hour) values were used as the response variables for optimization purposes. The interactions between concentration and temperature (P = 0.022), and pH and temperature (P = 0.010) for SGR, and interactions between concentration and temperature (P = 0.012) for SUR were found to be statistically significant. The optimal values for achieving high SGR (0.15 h−1) and SUR (0.3622 mg styrene mg−1 biomass h−1) were calculated from the regression model equation. Those values are C o = 89.1 mg l−1, pH = 5.4, and T = 31.5 °C for SGR and C o = 69.2 mg l−1, pH = 5.5, and T = 32.4 °C for SUR. It was also observed that the Exophiala strain degrades styrene via phenylacetic acid, involving initial oxidation of the vinyl side chain. Besides, in the presence of styrene, changes in the fatty acids profile were also observed. It is hypothesized that an increasing amount of linoleic acid (18:2) may be involved in the protection of the fungus against toxic substrate.