Screening of bacteria, isolated from PAH-contaminated soils, for production of biosurfactants and bioemulsifiers

Abstract

Fifty-seven bacterial strains were isolated from PAH-contaminated soils using PAl-I-amended minimal medium. The isolates were screened for their production of biosurfactants and bioemulsifiers when grown in liquid media containing selected PAHs. The results suggest that many, but not all, of the isolates are able to produce biosurfactants or bioemulsifiers under the experimental conditions. The majority of the strains isolated on phenanthrene, pyrene, and fluoranthene were better emulsifiers than surface tension reducers and the stability of the formed emulsions was in general high. The strains isolated on anthracene were in general better in lowering the surface tension than in forming emulsions. In all strains, reduction of surface tension and emulsion formation did not correlate. However, in the majority of strains the two factors were associated with the bacterial cell surfaces, rather than the culture supernatants. Nevertheless, supernatants from selected surfactant-producing anthracene isolates increased the aqueous solubility of anthracene. Although a significant potential for surfactant and emulsifier production in the microbiota of the PAH-contaminated soils was found in this study, the ability of individual strains to mineralize PAl-Is did not coincide with production of surface-active compounds.

Soy protein hydrolysis with microbial protease to improve antioxidant and functional properties

“…The capacity of the hydrolysates to emulsify hydrophobic substances was tested. Each hydrolysate was mixed with 2 mL of soybean oil and allowed to stand for 24 h at room temperature (Willumsen and Karlson 1997). After this time the emulsifying index (E24) was determined as: E24−(height of the layer/ height of the total)×100.…”

Isolation and characterization of halophilic Archaea able to produce biosurfactants

“…The criterion used for selecting biosurfactant producers is the ability to reduce the surface tension below 40 mN m-1 [16,9] while a criterion cited for emulsionstabilizing capacity is the ability to maintain at least 50% of the original emulsion volume 24 h after formation [56]. Strains were cultivated on the standard medium and screening of biosurfactant producing colonies was performed using the qualitative drop-collapse test described by Jain et al [33] after being modified by Bodour and Maier [9].…”

“…Also, Willumsen and Karlson [56], a criterion cited for emulsion-stabilizing capacity is the ability to maintain at least 50% of the original emulsion volume 24h after formation. The 2 strains tested produced extracellular biosurfactant and produced a strong biosurfactant capable of generating a stable emulsion over several hours.…”

The Potential of Bacterial Isolates for Emulsification with a Range of Hydrocarbons

“…Allen et al (37) found that all microbial isolates from subsurface soil contaminated with unleaded gasoline showed emulsification activity when overlaid with gasoline, whereas emulsification activity by microbial cultures overlaid with kerosene and diesel fuel were weaker. Willumsen and Karlson (40) found that 67% of their isolates were able to form detectable emulsions with diesel fuel. One might speculate that this relatively low percentage of emulsifiers among isolates from soil contaminated with PAH as opposed to soil contaminated with aliphatic hydrocarbons might indicate that growth on PAH does not require emulsification to the same extent as growth on aliphatic hydrocarbons.…”