Isolation and genetic identification of yeast producing biosurfactants, evaluated by different screening methods

The present study, investigated the potential application of yeast isolates for extracellular biosurfactant production. Twenty-five yeast isolates are primarily evaluated for their biosurfactant activity using ten screening analytical methods. Isolates 263, 27(1), 20(2) and 24(1) achieved maximum emulsification indexes of 59.65, 56.14, 52.63 and 47.37%, maximum diameters of oil free clearing zone at 2.25, 2.15, 2.03 and 1.89 cm, largest diameters of liquid droplets on the hydrophobic surface and significantly reduced surface tension of MSM from 90.93 to 51.64, 54.07, 57.45 and 62.40 mN m−1, respectively. The four isolates were hydrocarbon utilizers, lipase producers, showed no hemolytic activity while gave positive results in CTAB and phenol‑sulfuric acid tests, indicating that they produced anionic biosurfactant with possible glycolipid structure. Those promising isolates were identified by 18S rRNA gene amplification and sequencing analysis. Yeast isolates 263 and 27(1) were identified as Geotrichum candidum, 20(2) was Galactomyces pseudocandidum and 24(1) was Candida tropicalis.