Review Article Rhamnolipids: Production in bacteria other than Pseudomonas aeruginosa Jeiry Toribio 1 , Ana E. Escalante 2 and Gloria Sobero ´ n-Cha ´vez 1 1 Departamento de Biologı ´a Molecular y Biotecnologı ´a, Instituto de Investigaciones Biome ´ dicas, Universidad Nacional Auto ´noma de Me ´xico, Apartado, Mexico 2 Departamento de Ecologı ´a Evolutiva, Instituto de Ecologı ´a, Universidad Nacional Auto ´noma de Me ´xico, Apartado, Mexico Rhamnolipids produced by Pseudomonas aeruginosa are the most studied biosurfactants due to their potential applications in a wide variety of industries and the high levels of their production. However, even though these biosurfactants are already produced at an industrial scale, the fact that P. aeruginosa is an opportunistic pathogen impose a restriction for its large scale production due to the intrinsic health hazard of the process. Other bacterial species that have been reported to be rhamnolipid producers are the pathogens Burkholderia mallei and B. pseudomallei, and recently the non-pathogenic B. thailandensis. This short review presents information on rhamnolipid production by bacteria different from P. aeruginosa, as well as some approaches that have been taken to produce rhamnolipids using non-pathogenic bacteria by genetic engineering of different bacteria. The low frequency of occurrence of rhamnolipid production among natural isolates that are not P. aeruginosa or Burkholderia, as well as the absence of orthologs of the genes involved in rhamnolipid synthesis (rhl genes) among the hundreds of sequenced bacterial genomes, suggest that the rare reported cases of these type of rhamnolipid-producing bacteria have acquired this trait through horizontal gene transfer either from P. aeruginosa or from a member of Burkholderia. Keywords: heterologous production / Rhamnolipids / rhl genes Received: November 25, 2009 / Revised: May 13, 2010 / Accepted: June 19, 2010 DOI: 10.1002/ejlt.200900256 1 Rhamnolipids application in industry Surfactants are currently used in a wide variety of industries and they represent a huge market of several billion dollars each year. Recently, surfactants produced by microorganisms (bio- surfactants) have received special attention due to their low toxicity and biodegradability that makes them very good can- didates for specific uses in environmental biotechnology [1]. The most important limitation for the commercial use of biosurfactants is the high cost of their production, so at present their wide spread industrial production is not econ- omically feasible. The biosurfactant that has been studied in most detail is rhamnolipids synthesized by P. aeruginosa [2], and it is one of the three biosurfactants that are commercially available [3], together with sophorolipids and surfactin. Furthermore, these glycolipids are the only biosurfactant that have been approved by US Environmental Protection Agency for use in food products, cosmetics, and pharmaceuticals [3]. However, the commercial-scale production of rhamnolipids has the great disadvantage that they are currently produced by the opportunistic human pathogen P. aeruginosa that represent an important health problem [4]. In this short review we will present the reported cases of other type of bacteria that are rhamnolipids producers, and thus could represent an alternative for the production of this biosurfactant at an industrial scale, as well as some strategies to produce rhamnolipids using genetic engineering strategies. 2 Rhamnolipids production by P. aeruginosa P. aeruginosa is a g-proteobacteria that can be isolated from different habitats including water, soil, and plants, and it is also an opportunistic human pathogen causing serious nosocomial infections [4]. As stated above, this bacterium Correspondence: Dr. Gloria Sobero ´ n-Cha ´ vez, Departamento de Biologı ´a Molecular y Biotecnologı ´a, Instituto de Investigaciones Biome ´ dicas, Universidad Nacional Auto ´noma de Me ´xico, Apartado Postal 70228, DF, 04510, Mexico E-mail: gloria@biomedicas.unam.mx Fax: (52-55) 55506447 Abbreviations: HAAs, 3-(3-hydroxyalkanoyloxy)alkanoic acids; HSL, homoserine lactones; QSR, quorum sensing response; URPB, ‘‘uncommon’’-rhamnolipid producing bacteria 1082 Eur. J. Lipid Sci. Technol. 2010, 112, 1082–1087 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com