Synthesis of biosurfactants by bacterial cells: Heavy-metals tolerance and siderophores

Abstract

Environment unfriendly nature of chemical surfactants and pollution of the environment with heavy metals, especially from industries have become great challenges worldwide, hence the need for an urgent solution. This study aimed to search for novel strains exhibiting multiple industrial applications of heavy-metal tolerance, siderophore and biosurfactant capabilities. Soil samples were collected from industrial metal dumpsites and farmland soils. Isolation, enrichment and characterization of bacteria were carried out using biochemical and molecular techniques. Bacterial isolates were evaluated for heavy metals tolerance by agar-well diffusion and smear methods. Siderophore test was carried out using iron (III) chloride assay and isolates were employed in biosurfactant synthesis using solvent extraction method. Results showed that the prominent genus are Pseudomonas, Proteus, Staphylococcus and Micrococcus species. Resistance to heavy metals were observed to be higher at lower concentrations (100 mg/L) and reduced at higher concentrations (200–600 mg/L). Six isolates tolerated Ni at 600 mg/L and five bacterial isolates resisted Pb and Zn at 600 mg/L while other isolates displayed different inhibition zones. The evaluation of the isolates for siderophores synthesis revealed that only 5 bacterial isolates were positive. Among the positive biosurfactant producers, Burkholderia cepacia strain HB21 gave the highest biosurfactants yield (1.87 g/L and 0.96 g/L) while the least yield of 0.74 g/L and 0.38 g/L were produced by Achromobacter xylosoxidans strain 207–4B with and without agitation. These findings reveal that Burkholderia cepacia strain HB21 is a novel metal-tolerant strain with siderophore and biosurfactant producing potentials and may be useful for industrial applications