Karen Ray

Production of sophorolipid biosurfactants by multiple species of the Starmerella (Candida) bombicola yeast clade

Sophorolipids are carbohydrate-based, amphiphilic biosurfactants that are of increasing interest for use in environmentally benign cleaning agents. Sophorolipid production was tested for 26 strains representing 19 species of the Starmerella yeast clade, including Starmerella bombicola and Candida apicola, which were previously reported to produce sophorolipids. Five of the 19 species tested showed significant production of sophorolipids: S. bombicola, C. apicola, Candida riodocensis, Candida stellata and a new species, Candida sp. NRRL Y-27208. A high-throughput matrix-assisted laser desorption/ionization-time of flight MS assay was developed that showed S. bombicola and C. apicola to produce a lactone form of sophorolipid, whereas C. riodocensis, C. stellata and Candida sp. NRRL Y-27208 produced predominantly free acid sophorolipids. Phylogenetic analysis of sequences for the D1/D2 domains of the nuclear large subunit rRNA gene placed all sophorolipid-producing species in the S. bombicola subclade of the Starmerella clade.

Isolation and characterization of rhamnolipid‐producing bacterial strains from a biodiesel facility

Novel strains of rhamnolipid-producing bacteria were isolated from soils at a biodiesel facility on the basis of their ability to grow on glycerol as a sole carbon source. Strains were identified as Acinetobacter calcoaceticus, Enterobacter asburiae, Enterobacter hormaechei, Pantoea stewartii, and Pseudomonas aeruginosa. The strains of the former five species were found to produce rhamnolipids in quantities the same as, or similar to, coisolated strains of P. aeruginosa. Measurements of surface tension revealed that that emulsifying properties of these strains were similar to levels displayed by rhamnolipids produced by P. aeruginosa. Results of matrix-assisted laser desorption/ionization time-of-flight MS analyses revealed that the predominant compounds made by all strains were C10-C10 mono- and dirhamnolipids. Notably, E. hormaechei and one strain of A. calcoaceticus produced rhamnolipids in amounts similar to the pseudomonads. As all strains examined were from the same taxonomic class of Proteobacteria, further examination of this group may reveal many additional species not previously known to produce rhamnolipids in addition to novel strains of species currently known to produce rhamnolipids.