Characterization of rhamnolipids produced by wild-type and engineered Burkholderia kururiensis

Biosurfactants are a class of functional molecules produced and secreted by microorganisms, which play important roles in cell physiology such as flagellum-dependent or -independent bacterial spreading, cell signaling, and biofilm formation. They are amphipathic compounds and comprise a variety of chemical structures, including rhamnolipids, typically produced by Pseudomonas spp. and also reported within other bacterial genera. The present study is focused on Burkholderia kururiensis KP23ᵀ, a trichloroethylene (TCE)-degrading, N-fixing, and plant growth-promoting bacterium. Herein, we describe the production of rhamnolipids by B. kururiensis, and its characterization by LTQ-Orbitrap Hybrid Mass Spectrometry, a powerful tool that allowed efficient identification of molecular subpopulations, due to its high selectivity, mass accuracy, and resolving power. The population of rhamnolipids produced by B. kururiensis revealed molecular species commonly observed in Pseudomonas spp. and/or Burkholderia spp. In addition, this strain was used as a platform for expression of two Pseudomonas aeruginosa biosynthetic enzymes: RhlA, which directly utilizes β-hydroxydecanoyl-ACP intermediates in fatty acid synthesis to generate the HAA, and RhlB, the rhamnosyltransferase 1, which catalyzes the transfer of dTDP-L-rhamnose to β-hydroxy fatty acids in the biosynthesis of rhamnolipids. We show that rhamnolipid production by the engineered B. kururiensis was increased over 600 % when compared to the wild type. Structural analyses demonstrated a molecular population composed mainly of monorhamnolipids, as opposed to wild-type B. kururiensis and P. aeruginosa in which dirhamnolipids are predominant. We conclude that B. kururiensis is a promising biosurfactant-producing organism, with great potential for environmental and biotechnological applications due to its non-pathogenic characteristics and efficiency as a platform for metabolic engineering and production of tailor-made biosurfactants.