Differential Spreading of Rhamnolipid Congeners from Pseudomonas aeruginosa

Rhamnolipids are surfactants produced by many Pseudomonad bacteria, including the species Pseudomonas aeruginosa. These rhamnolipids are known to aid and enable numerous phenotypic traits that improve the survival of the bacteria that make them. These surfactants are also important for industrial products ranging from pharmaceuticals to cleaning supplies to cosmetics, to name a few. Rhamnolipids have structural diversity that leads to an array of congeners; however, little is known about the localization and distribution of these congeners in two-dimensional space. Differential distribution of congeners can reduce the uniformity of applications in industrial settings and create heterogeneity within biological communities. We examined the distribution patterns of combinations of rhamnolipids in commercially available mixtures, cell-free spent media, and colony biofilms using mass spectrometry. We found that even in the absence of cells, congeners exhibit different distribution patterns, leading to different rhamnolipid congener distributions on a surface. Congeners with shorter fatty acid chains were more centrally located, while longer chains were more heterogeneous and distally located. We found that congeners with similar structures can distribute differently. Within developing colony biofilms, we found rhamnolipid distribution patterns differed from cell-free environments, lacking simple trends noted in cell-free environments. Most strikingly, we found the distribution patterns of individual congeners in the colony biofilms to be diverse. We note that the congener distribution is far from homogeneous but composed of numerous local microenvironments of varied rhamnolipid congener composition.