Sophorolipid biosynthesis by Candida bombicola from industrial fatty acid residues

Yeast Candida bombicola is known to produce sophorolipids from a variety of saccharic and lipidic feed-stocks. In the current study, the influence of fatty acid carbon chain length, unsaturation, source of low-cost industrial lipid feed-stocks, and nickel content in lipid feed-stocks on sophorolipid production by C. bombicola were investigated. Saturated and monounsaturated C18 fatty acid gave the highest levels of sophorolipid production while fatty acids with more than one site of unsaturation gave much lower yields. Sophorolipid production was reduced when shorter (≤C16) and longer (≥C20) fatty acids were fed. The possibility of exploiting low-cost industrial wastes or by-products for sophorolipid production by batch or fed-batch processes was investigated. Tallow fatty acid residue was the best lipid feed-stock for sophorolipid production (120 g/L, fed-batch cultures), while coconut fatty acid residue resulted in the lowest production (40 g/L, fed-batch cultures). Co-feeding coconut fatty acid residue with other feed-stocks improved its substrate value in batch cultures. C. bombicola was tolerant to nickel contamination of up to 112.5 mg/L during sophorolipid production. Nickel contaminated stearic fatty acid residue was transformed to value added sophorolipid product while nickel was sequestered primarily in biomass for safe removal and recovery. Sophorolipid product obtained from nickel contaminated lipid wastes had low nickel levels (<5 mg/L) that could allow its use in low-end consumer products and household applications.