Abstract
Heterologeous production of rhamnolipids in Pseudomonas putida is characterized by advantages of a non-pathogenic host and avoidance of the native quorum sensing regulation in Pseudomonas aeruginosa. Yet, downstream processing is a major problem in rhamnolipid production and increases in complexity at low rhamnolipid titers and when using chemical foam control. This leaves the necessity of a simple concentrating and purification method. Foam fractionation is an elegant method for in situ product removal when producing microbial surfactants. However, up to now in situ foam fractionation is nearly exclusively reported for the production of surfactin with Bacillus subtilis. So far no cultivation integrated foam fractionation process for rhamnolipid production has been reported. This is probably due to excessive bacterial foam enrichment in that system. In this article a simple integrated foam fractionation process is reported for heterologous rhamnolipid production in a bioreactor with easily manageable bacterial foam enrichments. Rhamnolipids were highly concentrated in the foam during the cultivation process with enrichment factors up to 200. The described process was evaluated at different pH, media compositions and temperatures. Foam fractionation processes were characterized by calculating procedural parameter including rhamnolipid and bacterial enrichment, rhamnolipid recovery, YX/S, YP/X, and specific as well as volumetric productivities. Comparing foam fractionation parameters of the rhamnolipid process with the surfactin process a high effectiveness of the integrated foam fractionation for rhamnolipid production was demonstrated.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0183-2) contains supplementary material, which is available to authorized users.
Highlights
Consumer concern for renewable sources of products gained importance in the past
Rhamnolipids contain one or two rhamnose moieties glycosidically bound to a lipid moiety made out of one, two or three β-hydroxy fatty acid chains which are in turn bound together through an ester bound (Abdel-Mawgoud et al 2010)
Production kinetics Comparing the two different media, pH values and temperature conditions used in this study different rhamnolipid production kinetics could be detected
Summary
Consumer concern for renewable sources of products gained importance in the past. Produced biosurfactants with their renewable raw material meet costumers requests. Rhamnolipids are one of the most intensively studied microbial produced biosurfactants. Rhamnolipids lower surface tension of water from 72 to 25–30 mN m−1 and exhibit CMCs Bergström et al (1946) firstly described rhamnolipids and the structure of rhamnolipids was elucidated by Jarvis and Johnson (1949). Rhamnolipids contain one or two rhamnose moieties glycosidically bound to a lipid moiety made out of one, two or three β-hydroxy fatty acid chains which are in turn bound together through an ester bound (Abdel-Mawgoud et al 2010). Beuker et al AMB Expr (2016) 6:11
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