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.
Abstract:
The efficiency of biosurfactant-facilitated removal of soil-bound metals is affected by biosurfactant sorption to soil. In this study, batch and column experiments were performed to minimize rhamnolipid biosurfactant sorption and to optimize rhamnolipid application for removal of cadmium from four soils. In batch studies, rhamnolipid sorption to a model coarse loamy soil was found to vary with applied rhamnolipid and K+ concentration of the rhamnolipid matrix. The presence of solution-phase biosurfactant was correlated to the release into solution of a soil-bound metal (cadmium). A series of column experiments was performed to evaluate whether rhamnolipid could remove cadmium from soil under saturated flow conditions. Four different soils were contaminated with cadmium and treated first with an KNO3 electrolyte solution (3.5 or 7 mM K+) and then with a rhamnolipid- containing solution (5 or 10 mM). Results showed that between 15 and 36% of the cadmium was removed by the initial electrolyte treatment and an additional 8-54% of the cadmium was removed by rhamnolipid treatment. Rhamnolipid treatment was very effective for three of the soils tested, but for the soil with the highest clay content, rhamnolipid application caused soil dispersion and column plugging.
