Selection of biosurfactan/bioemulsifier-producing bacteria from hydrocarbon-contaminated soil

Abstract

Petroleum-derived hydrocarbons are among the most persistent soil contaminants, and some hydrocarbondegrading microorganisms can produce biosurfactants to increase bioavailability and degradation. The aim of this work was to identify biosurfactant-producing bacterial strains isolated from hydrocarboncontaminated sites, and to evaluate their biosurfactant properties. The drop-collapse method and minimal agar added with a layer of combustoleo were used for screening, and positive strains were grown in liquid medium, and surface tension and emulsification index were determined in cell-free supernantant and cell suspension. A total of 324 bacterial strains were tested, and 17 were positive for the drop-collapse and hydrocarbon-layer agar methods. Most of the strains were Pseudomonas, except for three strains (Acinetobacter, Bacillus, Rhodococcus). Surface tension was similar in cell-free and cell suspension measurements, with values in the range of 58 to 26 (mN/m), and all formed stable emulsions with motor oil (76-93% E 24 ). Considering the variety of molecular structures among microbial biosurfactants, they have different chemical properties that can be exploited commercially, for applications as diverse as bioremediation or degradable detergents.

Isolation of Surfactant-Resistant Pseudomonads from the Estuarine Surface Microlayer

“…The excretion of biosurfactants is considered an adaptation to interfacial life, increasing cell hydrophobicity and improving floatation and dispersion [26,79]. Attempts to isolate surfactantresistant bacteria from surfactant-rich environments [7,48,72], and biosurfactant-producing strains from environments enriched in hydrophobic substrates [54], are documented in the literature. However, the SML remains a rather unexplored compartment in both the perspectives.…”

“…However, hydrophobic substrates are not a prerequisite for biosurfactant production [74], and biosurfactant-producing microorganisms have been isolated with other carbon sources, namely, Zobell medium [21], nutrient agar [1], minimal medium with glucose [13,25], and PY medium amended with synthetic surfactants [54]. Some of the attempts to use hydrophobic carbon sources in selective or enrichment media have also achieved modest percentages of positive results, despite intense screening efforts: less than 10% of the isolates from oil-contaminated soils [48,72,77], 4% from oil-spilled seawater [46], and 9.2% from terrestrial and marine samples [7]. A high percentage of surfactantproducing isolates (73.8%) was retrieved from the guts of sea polychaetes [54], but the concentrations produced were very low, and since the method used for the detection was the oil-spreading assay [81], the results can hardly be compared.…”

“…Because of their environmental and technical advantages relative to their synthetic counterparts [56], biosurfactants have gained biotechnological and economical interest. Therefore, the prospection for new biosurfactants-producing strains has more recently been directed to hydrocarbon-contaminated sites [63,72], marine environments [54,63], and uncommon or extreme microbial habitats [36,40,71]. Pseudomonads include oil-degrading and biosurfactant (rhamnolipids)-producing strains and are frequently found in oil-impacted marine sites [27].…”

Microbiotechnology Based Surfactants and Their Applications

“…Using the emulsification index E 24 test, Viramontes-Ramos et al (2010) identified six isolates that could efficiently emulsify different hydrocarbons (more than 50% against diesel, decane, kerosene and motor oil) without showing a significant reduction in surface tension of their culture broths. The emulsifying potential of surface active compounds from different yeasts showing no reduction in surface tension, has been evaluated using the emulsification index test (Amaral et al, 2006;Monteiro et al, 2010).…”

Drop collapse assay on lotus leaf (Nelumbo nucifera): a simple and cost effective method for rapid detection of biosurfactants

“…Biosurfactant producing microorganisms are collected from natural environments using various established methods such as drop collapse assay, microplate assay, penetration assay, oil spread method, solubilization of crystalline anthracene, etc. (Van Hamme & Ward, 2001;Youssef et al, 2004;Walter et al, 2010;Viramontes-Ramos et al, 2010). In present study drop collapse assay was modified with an intention to make it rapid and cost effective to overcome some limitations in the existing assay (Jain et al, 1991).…”