Abstract:
Biodegradation rates for polycyclic aromatic hydrocarbons (PAH) in the environment are limited by their low solubility and sorption to solid surfaces. The purpose of this study was to quantify the effect of biosurfactants on the dissolution, bioavailability, and biodegradation of a slightly soluble PAH, phenanthrene, in a series of batch solution studies. A mathematical model that describes the combined effects of solubilization and biodegradation, including description of bioavailability within surfactant micelles, was used to analyze the experimental results. Two forms of the biosurfactant, a monorhamnolipid and a dirhamnolipid, were tested; it was found that both surfactants increased the solubility and enhanced the rate of phenanthrene biodegradation. Monorhamnolipid was more effective than dirhamnolipid for solubilization; however, overall rates of mineralization were essentially the same. This seems to result from variable bioavailability of substrate: phenanthrene within monorhamnolipid micelles was less bioavailable than phenanthrene within dirhamnolipid micelles. Therefore, the effect of a surfactant on biodegradation is s combination of the solubilizing power of the surfactant and the bioavailability of the substrate within the surfactant micelles. Model analysis of the solubilization data showed that the overall solubilization rate coefficient, K(L), increased with increasing biosurfactant concentration. Analysis of biodegradation data showed that enhanced biodegradation rates depend upon both K(L) and α, the coefficient for substrate bioavailability from micelles. Model simulations using parameters developed from test data are discussed.
PMID: 17186153;Abstract:
Kartchner Caverns in Benson, AZ, was opened for tourism in 1999 after a careful development protocol that was designed to maintain predevelopment conditions. As a part of an ongoing effort to determine the impact of humans on this limestone cave, samples were collected from cave rock surfaces along the cave trail traveled daily by tour groups (200,000 visitors year-1) and compared to samples taken from areas designated as having medium (30-40 visitors year-1) and low (2-3 visitors year-1) levels of human exposure. Samples were also taken from fiberglass moldings installed during cave development. Culturable bacteria were recovered from these samples and 90 unique isolates were identified by using 16S rRNA polymerase chain reaction and sequencing. Diversity generally decreased as human impact increased leading to the isolation of 32, 27, and 22 strains from the low, medium, and high impact areas, respectively. The degree of human impact was also reflected in the phylogeny of the isolates recovered. Although most isolates fell into one of three phyla: Actinobacteria, Firmicutes, or Proteobacteria, the Proteobacteria were most abundant along the cave trail (77% of the isolates), while Firmicutes predominated in the low (66%) and medium (52%) impact areas. Although the abundance of Proteobacteria along the cave trail seems to include microbes of environmental rather than of anthropogenic origin, it is likely that their presence is a consequence of increased organic matter availability due to lint and other organics brought in by cave visitors. Monitoring of the cave is still in progress to determine whether these bacterial community changes may impact the future development of cave formations. © 2006 Springer Science+Business Media, Inc.
PMID: 11010924;PMCID: PMC92350;Abstract:
A model cocontaminated system was developed to determine whether a metal-complexing biosurfactant, rhamnolipid, could reduce metal toxicity to allow enhanced organic biodegradation by a Burkholderia sp. isolated from soil. Rhamnolipid eliminated cadmium toxicity when added at a 10-fold greater concentration than cadmium (890 μM), reduced toxicity when added at an equimolar concentration (89 μM), and had no effect at a 10-fold smaller concentration (8,9 μM). The mechanism by which rhamnolipid reduces metal toxicity may involve a combination of rhamnolipid complexation of cadmium and rhamnolipid interaction with the cell surface to alter cadmium uptake.
