Ultrafiltration based purification strategies for surfactin produced by Bacillus subtilisLB5A using cassava wastewater as substrate

Abstract

BACKGROUND Bacillus subtilis synthesizes surfactin, a powerful surface‐active agent. It has interesting potential applications. However, due to its high cost of production, commercial use is impracticable. The downstream processing represents ≈ 60% of production costs and the culture medium ≈ 30%. Many reports focused, separately, on production of surfactin using by‐products (reduced cost) or the purification using synthetic medium. Therefore, the aim of this work was to evaluate, for the first time, the impact of using a by‐product as fermentation medium on the downstream processing based on membrane filtration. RESULTS Membranes of PES‐100‐kDa efficiently retained surfactin micelles – the first step of ultrafiltration, whereas, the second step required membranes of 50 kDa to separate surfactin monomers from proteins. Ultrafiltration of crude biosurfactant was associated with fouling and/or concentration polarization resulting in lower purity than when synthetic medium was used. Further improvement in purity was achieved by partial removal of proteins before ultrafiltration by acid precipitation and extraction. The NMR and MALDI‐TOFMS analyses identified 11 potential surfactin homologues composed of two amino acid sequences. CONCLUSION Production of surfactin using cassava wastewater as a low‐cost culture medium and its purification by the 2‐step ultrafiltration process is feasible, nevertheless, the higher protein content of this medium compared with the synthetic one leads to a lower purity product; further increase in purity can be achieved by applying additional purification steps prior to ultrafiltration with subsequent increased process cost. © 2016 Society of Chemical Industry

Comparative study: bench-scale surfactin production from bacillus subtilis using analytical grade and concentrated glycerol from the biodiesel industry

“…All culture media were adjusted to pH 7 with NaOH 0.05 M. The erlenmeyer flasks, containing each culture medium (100 mL), were inoculated and then incubated at 150 rpm and 30 o C. Samples (≈ 12 mL) of the culture medium were collected on a 12-hour basis and centrifuged at 10 4 g for 10 minutes at 5 o C. Finally, the viable cell count, surface tension (ST) of the samples and their dilutions were analyzed [15][16][17].…”

“…The process conditions were: 150 rpm, 30 o C and an aeration rate (air) of 0.266 vvm (maximum aeration pump capacity available) [16][17]. The dissolved oxygen (DO) sensor (Mettler Toledo -INPRO 6830/12/320) was set to measure every thirty seconds during the entire fermentation process.…”

“…The dissolved oxygen (DO) sensor (Mettler Toledo -INPRO 6830/12/320) was set to measure every thirty seconds during the entire fermentation process. Samples (≈ 30 mL) of the culture medium were collected on a 24-hour basis, and subsequently the viable cell count, ST dilutions and consumption of glycerol were used as process parameters [2], [15][16][17]. Foam was collected during production from the top of the bench-scale bioreactor (foam overflow) into a Büchner flask through a hose [15][16].…”

“…Samples (≈ 30 mL) of the culture medium were collected on a 24-hour basis, and subsequently the viable cell count, ST dilutions and consumption of glycerol were used as process parameters [2], [15][16][17]. Foam was collected during production from the top of the bench-scale bioreactor (foam overflow) into a Büchner flask through a hose [15][16]. The foam volume was measured on a 24-hour basis, centrifuged (10 4 g for 10 minutes at 5 o C) and had its surface activity (ST and its dilution) measured.…”

“…Two purification methods were applied: (1) acid precipitation method and (2) acid precipitation followed by solvent extraction (chloroform: methanol-81:19) and solvent evaporation [15][16][17]. The resulting product (in powder form) from (1) was named crude biosurfactant and the product from (2) semi-purified biosurfactant.…”