Rhamnolipid production from waste cooking oil using Pseudomonas SWP-4

• Pseudomonas SWP-4 could produce rhamnolipid from waste cooking oil.
• Pseudomonas SWP-4 accumulated rhamnolipid steadily even in decline phase.
• Pseudomonas SWP-4 gave a maximum rhamnolipid yield of 13.93 g/L.
• The produced rhamnolipid showed excellent surface activity and stability.
• Biodegradation of waste cooking oil is a promising way of waste treatment.

The present work aims to produce rhamnolipid from waste cooking oil (WCO) using a newly isolated bacterium named Pseudomonas SWP-4. SWP-4 was a high-yield strain that could accumulate rhamnolipid steadily even in decline phase and gave a maximum rhamnolipid yield of 13.93 g/L and WCO utilization percent around 88%. The critical micelle concentration of the produced rhamnolipid was only 27 mg/L and its emulsification index against n-hexadecane reached around 59%. Moreover, it reduced the surface tension of water from 71.8 mN/m to 24.1 mN/m and the interfacial tension against n-hexadecane from 29.4 mN/m to 0.9 mN/m. Results of biosurfactant stability show the rhamnolipid was effective when the salinity was lower than 8% and pH value ranged from 4 to 10, and it was quite thermostable based on thermal gravity analysis. Furthermore, it maintained high surface activity even after incubation under extreme conditions i.e., pH of 4.0, salinity of 8% and temperature of 80 °C for half a month. Based on free fatty acids metabolism analysis, Pseudomonas SWP-4 consumed palmitic acid, oleic acid and linoleic acid chiefly. All these characteristics demonstrate bioconversion and biodegradation of WCO by Pseudomonas SWP-4 is a promising and commercial way of rhamnolipid production and waste treatment.

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