Rhamnolipids: diversity of structures, microbial origins and roles

Abstract

Rhamnolipids are glycolipidic biosurfactants produced by various bacterial species. They were initially found as exoproducts of the opportunistic pathogen Pseudomonas aeruginosa and described as a mixture of four congeners: α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-Rha-C10-C10), α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoate (Rha-Rha-C10), as well as their mono-rhamnolipid congeners Rha-C10-C10 and Rha-C10. The development of more sensitive analytical techniques has lead to the further discovery of a wide diversity of rhamnolipid congeners and homologues (about 60) that are produced at different concentrations by various Pseudomonas species and by bacteria belonging to other families, classes, or even phyla. For example, various Burkholderia species have been shown to produce rhamnolipids that have longer alkyl chains than those produced by P. aeruginosa. In P. aeruginosa, three genes, carried on two distinct operons, code for the enzymes responsible for the final steps of rhamnolipid synthesis: one operon carries the rhlAB genes and the other rhlC. Genes highly similar to rhlA, rhlB, and rhlC have also been found in various Burkholderia species but grouped within one putative operon, and they have been shown to be required for rhamnolipid production as well. The exact physiological function of these secondary metabolites is still unclear. Most identified activities are derived from the surface activity, wetting ability, detergency, and other amphipathic-related properties of these molecules. Indeed, rhamnolipids promote the uptake and biodegradation of poorly soluble substrates, act as immune modulators and virulence factors, have antimicrobial activities, and are involved in surface motility and in bacterial biofilm development.

Produção de biossurfactantes por microrganismos isolados de solo contaminado com óleo diesel

“…Isso se reflete na poluição do solo e das águas superficiais e subterrâneas. 1,2 Os biossurfactantes são compostos microbianos que possuem uma porção hidrofóbica e outra hidrofílica, [3][4][5][6] exibindo alta atividade surfactante e emulsificante, 7 sendo adicionados ao ambiente para estimular o processo de biorremediação, tornando os poluentes disponíveis à biodegradação. 8 Os compostos oleosos são degradados por microrganismos capazes de utilizar hidrocarbonetos como fonte de carbono para obtenção de energia.…”

“…7,19 Os biossurfactantes apresentam vantagens relacionadas à baixa toxicidade, alta biodegradabilidade, variedade de estruturas quí-micas, estabilidade em condições extremas de pH, temperatura e salinidade. 3,8,18 Dentre os problemas relacionados ao uso de biossurfactantes está o seu alto custo de produção, associado a métodos ineficientes de recuperação do produto e ao uso de substratos caros. A diminuição dos custos de produção destes compostos pode ser realizada a partir da otimização dos processos e dos meios de cultivo utilizados.…”

Rhamnolipids, Microbial Virulence Factors, in Alzheimer’s Disease

“…RLs production is regulated by the quorum sensing system depending on the bacterial density in the culture medium [33]. They are released from the periplasm toward the extracellular environment and have been characterized as bacterial virulence factors [32]. Several biological activities of RLs emanating from and being attributed to their detergent-like properties have been identified [30,34], including immune system modulation [34]; promotion of early infiltration of primary human airway epithelia by P. aeruginosa; morphological alterations in the membrane provoking alterations to its integrity especially by causing selective tight-junction changes to the respiratory epithelium [35]; cytotoxicity induced on the fibroblastic cell line [36]; hemolytic activity of erythrocytes [37]; and induction of cytogenetic damage in human lymphocytes and bind DNA in vitro [38].…”

“…RLs are glycolipids, initially reported to be produced by P. aeruginosa, but later several other bacteria were added to the list [30][31][32][33]. RLs are composed of a gluconic and a lipidic segment, commonly comprising one or two rhamnoses and hydroxyl-substituted fatty acids [33].…”

EXTRACCIÓN DE PETRÓLEO EN SUELO CONTAMINADO EMPLEANDO RAMNOLÍPIDOS PRODUCIDOS POR Pseudomonas aeruginosa ORA9

“…Los ramnolípidos, junto a otro grupo de biocompuestos tensoactivos producidos por bacterias y hongos, son conocidos como biosurfactantes. Los ramnolípidos son completamente biodegradables, de baja toxicidad, se obtienen biotecnológicamente a partir de residuales, son estables y muestran propiedades superficiales superiores a los tensoactivos de origen sintético, los cuales, además de dominar el mercado, han mostrado ser persistentes en el ambiente, tóxicos y no sustentables por ser petroderivados (Abdel et al 2010).…”