[Effects of surfactants on the biodegradation of phenol by Candida tropicalis]

The method of liquid fermentation culture was used to study the influence of two synthetic surfactants, cetyl trimethylammonium bromide (CTAB) and Triton X-100, and a biosurfactant, dirhamnlipid (diRL), on phenol degradation by Candida tropicalis CICC 1463. The results showed that at the beginning of degradation the yeast population decayed, phenol metabolization and bacterial growth did not occur simultaneously, which indicated the toxicity of phenol and formation of intermediate product. CTAB was toxic to C. tropicalis, and it restrained phenol removal. The phenol degradation was accelerated by Triton X-100 of low concentrations of 0.1 and 0.3 CMC, and the complete degradation was achieved at 24 h and 36 h, respectively, compared to 48 h of control. When Triton X-100 concentration was increased to 1.0 CMC or higher concentration, decay of yeast in the initial phase was weakened, but phenol removal and bacterial growth were lagged. The biosurfactant diRL enhanced phenol degradation and growth of the C. tropicalis markedly, and the effect increased with increasing of diRL concentration. Complete degradation was achieved at 24 h in the presence of 1.0 and 3.0 CMC diRL. The diRL concentration also decreased gradually during the fermentation. These results indicated that diRL could reduce phenol toxicity to a great extent and favor the bacterial growth as co-substrate.