PMID: 12788727;PMCID: PMC161513;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 R2A 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.
Direct revegetation, or phytostabilization, is a containment strategy for contaminant metals associated with mine tailings in semiarid regions. The weathering of sulfide ore-derived tailings frequently drives acidification that inhibits plant establishment resulting in materials prone to wind and water dispersal. The specific objective of this study was to associate pyritic mine waste acidification, characterized through pore-water chemistry analysis, with dynamic changes in microbial community diversity and phylogenetic composition, and to evaluate the influence of different treatment strategies on the control of acidification dynamics. Samples were collected from a highly instrumented one-year mesocosm study that included the following treatments: 1) unamended tailings control; 2) tailings amended with 15% compost; and 3) the 15% compost-amended tailings planted with Atriplex lentiformis. Tailings samples were collected at 0, 3, 6 and 12months and pore water chemistry was monitored as an indicator of acidification and weathering processes. Results confirmed that the acidification process for pyritic mine tailings is associated with a temporal progression of bacterial and archaeal phylotypes from pH sensitive Thiobacillus and Thiomonas to communities dominated by Leptospirillum and Ferroplasma. Pore-water chemistry indicated that weathering rates were highest when Leptospirillum was most abundant. The planted treatment was most successful in disrupting the successional evolution of the Fe/S-oxidizing community. Plant establishment stimulated growth of plant-growth-promoting heterotrophic phylotypes and controlled the proliferation of lithoautotrophic Fe/S-oxidizers. The results suggest the potential for eco-engineering a microbial inoculum to stimulate plant establishment and inhibit proliferation of the most efficient Fe/S-oxidizing phylotypes.
PMID: 11131386;Abstract:
Pseudomonas aeruginosa produces and secretes rhamnose-containing glycolipid biosurfactants called rhamnolipids. This review describes rhamnolipid biosynthesis and potential industrial and environmental applications of rhamnolipids. Rhamnolipid production is dependent on central metabolic pathways, such as fatty acid synthesis and dTDP-activated sugars, as well as on enzymes participating in the production of the exopolysaccharide alginate. Synthesis of these surfactants is regulated by a very complex genetic regulatory system that also controls different P. aeruginosa virulence-associated traits. Rhamnolipids have several potential industrial and environmental applications including the production of fine chemicals, the characterization of surfaces and surface coatings, as additives for environmental remediation, and as a biological control agent. Realization of this wide variety of applications requires economical commercial-scale production of rhamnolipids.
PMID: 11764852;Abstract:
Development of environmentally benign approaches to remediation of metal-contaminated soils and sewage sludges are needed to replace currently used techniques of either landfilling or metal extraction using caustic or toxic agents. We report results from four application technologies that use a metal-chelating biosurfactant, rhamnolipid, for removal of metals or metal-associated toxicity from metal-contaminated waste. The four applications include: 1) removal of metals from sewage sludge; 2) removal of metals from historically contaminated soils; 3) combined biosurfactant/phytoremediation of metal-contaminated soil; and 4) use of biosurfactant to facilitate biodegradation of the organic component of a metal-organic co-contaminated soil (in this case the biosurfactant reduces metal toxicity). These four technologies are nondestructive options for situations where the final goal is the removal of bioavailable and leachable metal contamination while maintaining a healthy ecosystem. Some of the approaches outlined may require multiple treatments or long treatment times which must be acceptable to site land-use plans and to the stakeholders involved. However, the end-product is a soil, sediment, or sludge available for a broad range of land use applications.
PMID: 12676702;PMCID: PMC154800;Abstract:
One limitation of employing lux bioreporters to monitor in situ microbial gene expression in dynamic, lab. oratory-scale systems is the confounding variability in the luminescent responses. For example, despite careful control of oxygen tension, growth stage, and cell number, luminescence from Pseudomonas putida RB1353, a naphthalene-degrading lux bioreporter, varied by more than sevenfold during saturated flow column experiments in our laboratory. Therefore, this study was conducted to determine what additional factors influence the luminescent response. Specifically, this study investigated the impact of temperature, pH, and initial cell number (variations within an order of magnitude) on the peak luminescence of P. putida RB1353 and the maximum degradation rate (Vmax) during salicylate and naphthalene catabolism. Statistical analyses based on general linear models indicated that under constant oxygen tension, temperature and pH accounted for 98.1% of the variability in luminescence during salicylate catabolism and 94.2 and 49.5% of the variability in Vmax during salicylate and naphthalene catabolism, respectively. Temperature, pH, and initial substrate concentration accounted for 99.9% of the variability in luminescence during naphthalene catabolism. Initial cell number, within an order of magnitude, did not have a significant influence on either peak luminescence or Vmax during salicylate and naphthalene catabolism. Over the ranges of temperature and pH evaluated, peak luminescence varied by more than 4 orders of magnitude. The minimum parameter deviation required to alter lux gene expression during salicylate and naphthalene catabolism was a change in temperature of 1°C, a change in pH of 0.2, or a change in initial cell number of 1 order of magnitude. Results from this study indicate that there is a need for careful characterization of the impact of environmental conditions on both the expression of the reporter and catabolic genes and the activities of the gene products. For example, even though lux gene expression was occurring at ∼35°C, the luciferase enzyme was inactive. Furthermore, this study demonstrates that with careful characterization and standardization of measurement conditions, the attainment of a reproducible luminescent response and an understanding of the response are feasible.
