Distribution of Biosurfactant-Producing Bacteria in Undisturbed and Contaminated Arid Southwestern Soils

Abstract

Biosurfactants are a unique class of compounds that have been shown to have a variety of potential applications in the remediation of organic-and metal-contaminated sites, in the enhanced transport of bacteria, in enhanced oil recovery, as cosmetic additives, and in biological control. However, little is known about the distribution of biosurfactant-producing bacteria in the environment. The goal of this study was to determine how common culturable surfactant-producing bacteria are in undisturbed and contaminated sites. A series of 20 contaminated (i.e., with metals and/or hydrocarbons) and undisturbed soils were collected and plated on R 2 A agar. The 1,305 colonies obtained were screened for biosurfactant production in mineral salts medium containing 2% glucose. Forty-five of the isolates were positive for biosurfactant production, representing most of the soils tested. The 45 isolates were grouped by using repetitive extragenic palindromic (REP)-PCR analysis, which yielded 16 unique isolates. Phylogenetic relationships were determined by comparing the 16S rRNA gene sequence of each unique isolate with known sequences, revealing one new biosurfactant-producing microbe, a Flavobacterium sp. Sequencing results indicated only 10 unique isolates (in comparison to the REP analysis, which indicated 16 unique isolates). Surface tension results demonstrated that isolates that were similar according to sequence analysis but unique according to REP analysis in fact produced different surfactant mixtures under identical growth conditions. These results suggest that the 16S rRNA gene database commonly used for determining phylogenetic relationships may miss diversity in microbial products (e.g., biosurfactants and antibiotics) that are made by closely related isolates. In summary, biosurfactant-producing microorganisms were found in most soils even by using a relatively limited screening assay. Distribution was dependent on soil conditions, with gram-positive biosurfactant-producing isolates tending to be from heavy metal-contaminated or uncontaminated soils and gram-negative isolates tending to be from hydrocarbon-contaminated or cocontaminated soils.

Screening, stability and antibacterial potential of rhamnolipids from Pseudomonas sp., isolated from hydrocarbon contaminated soil

“…Amiriyan et al (2004) reported 11 biosurfactant producers from Iranian oil reservoirs. The present findings are in accordance with the findings of Bodour et al (2003) and Amiriyan et al (2004). However, findings of Ramesh et al (2010) was contrary from this study who reported biosurfactant only in hydrocarbon contaminated soil.…”

“…A total of seven biosurfactant producing isolates were obtained from soil and oil samples. Bodour et al (2003) obtained 45 biosurfactant producing isolates from hydrocarbon contaminated South Western soils of Arizona and most of the surfactant producing isolates was tending from contaminated and co-contaminated soil. Amiriyan et al (2004) reported 11 biosurfactant producers from Iranian oil reservoirs.…”

“…Carrillo et al (1996) found an association between hemolytic activity and surfactant production, and they recommended the use of blood agar lysis as a primary screening. Bodour et al (2003) used drop collapse assay for screening surfactant producing isolates, they emulsified the coated oil in culture broth and made micro emulsion. Because of the formation of micro emulsions, the culture drops collapsed in coated oil.…”

“…Periodically 1 ml of sample was drawn at regular interval and serially diluted in sterile saline. 0.1 ml of diluted sample was spread plated onto nutrient agar medium and incubated for 7 days at room temperature (Bodour et al, 2003). For the isolation of bacteria from oil, 1 ml of oil sample was added into 9 ml of sterile saline and the mixture was placed on shaker for 1 h to produce well dispersed suspension (Amiriyan et al, 2004).…”

A glycolipid biosurfactant from a native halophilic Bacillus species of Porto Novo, India and its potential microbially enhanced oil recovery properties

“…Usually, different microbial genera synthesize structurally different classes of biosurfactants whereas strains belonging to a same species produce structurally similar biosurfactants. However, small differences in the molecular structures can have major impact on the functions and potential industrial applications of biosurfactants (Bodour et al, 2003).…”