Isolation and characterization of biosurfactant-producing bacteria from the Thar Desert

The Thar Desert, one of the most extreme arid ecosystems, harbours a diverse and resilient microbial community adapted to high temperatures, low moisture, and osmotic stress. In this study, soil samples collected from sand dunes in Churu, Rajasthan, were explored for the isolation of biosurfactant-producing bacteria. A total of ten morphologically distinct bacterial isolates were obtained and screened for biosurfactant activity using drop collapse (DC), emulsification index percentage (EA₂₄) %, surface tension (ST), and interfacial tension (IFT) assays. Among them, three isolates S4, S6, and S9 displayed significant biosurfactant activity. Isolate S9 recorded the highest activity with an EA₂₄% of 57.16 ± 2.63%, ST of 24.61 ± 1.2 mNm^-1, and IFT of 4.42 ± 1.26 mNm^-1, followed by S6 with an EA₂₄% of 54.13 ± 3.7%, ST of 26.64 ± 2.09 mNm^-1, and IFT of 5.81 ± 1.71 mNm^-1. Isolate S4 showed an EA₂₄% of 51.83 ± 1.8%, ST of 27.87 ± 1.5 mNm^-1, and IFT of 7.39 ± 1.31 mNm^-1. The molecular identification through 16S rRNA gene sequencing confirmed that S4 corresponds to Cytobacillus kochii, S6 to Acinetobacter soli, and S9 to Bacillus cereus. These strains demonstrated considerable potential for biotechnological applications, including bioremediation of hydrophobic pollutants and sustainable agriculture. The findings highlight the Thar Desert as an underexplored reservoir of extremophilic, surface-active compound-producing bacteria with noteworthy ecological and industrial relevance.