The presence of toxic metals in natural environments presents a potential health hazard for humans. Metal contaminants in these environments are usually tightly bound to colloidal particles and organic matter. This represents a major constraint to their removal using currently available in situ remediation technologies. One technique that has shown potential for facilitated metal removal from soil is treatment with an anionic microbial surfactant, rhamnolipid. Successful application of rhamnolipid in metal removal requires knowledge of the rhamnolipid-metal complexation reaction. Therefore, our objective was to evaluate the biosurfactant complexation affinity for the most common natural soil and water cations and for various metal contaminants. The conditional stability constant (log K) for each of these metals was determined using an ion-exchange resin technique. Results show the measured stability constants follow the order (from strongest to weakest): Al3+ > Cu2+ > Pb2+ > Cd2+ > Zn2+ > Fe3+ > Hg2+ > Ca2+ > Co2+ > Ni2+ > Mn2+ > Mg2+ > K+. These data indicate that rhamnolipid will preferentially complex metal contaminants such as lead, cadmium, and mercury in the presence of common soil or water cations. The measured rhamnolipid-metal stability constants were found in most cases to be similar or higher than conditional stability constants reported in the literature for metal complexation with acetic acid, oxalic acid, citric acid, and fulvic acids. These results help delineate the conditions under which rhamnolipid may be successfully applied as a remediation agent in the removal of metal contaminants from soil, as well as surface waters, ground water, and wastestreams.

No abstract

The overwhelming taxonomic diversity and metabolic complexity of microorganisms can be simplified by a life-history classification; copiotrophs grow faster and rely on resource availability, whereas oligotrophs efficiently exploit resource at the expense of growth rate. Here, we hypothesize that community-level traits inferred from metagenomic data can distinguish copiotrophic and oligotrophic microbial communities. Moreover, we hypothesize that oligotrophic microbial communities harbor more unannotated genes. To test these hypotheses, we conducted metagenomic analyses of soil samples collected from copiotrophic vegetated areas and from oligotrophic bare ground devoid of vegetation in an arid-hyperarid region of the Sonoran Desert, Arizona, USA. Results supported our hypotheses, as we found that multiple ecologically informed life-history traits including average 16S ribosomal RNA gene copy number, codon usage bias in ribosomal genes and predicted maximum growth rate were higher for microbial communities in vegetated than bare soils, and that oligotrophic microbial communities in bare soils harbored a higher proportion of genes that are unavailable in public reference databases. Collectively, our work demonstrates that life-history traits can distill complex microbial communities into ecologically coherent units and highlights that oligotrophic microbial communities serve as a rich source of novel functions.

Asthma increased dramatically in the last decades of the 20th century and is representative of chronic diseases that have been linked to altered microbial exposure and immune responses. Here we evaluate the effects of environmental exposures typically associated with asthma protection or risk on the microbial community structure of household dust (dogs, cats, and day care). PCR-denaturing gradient gel analysis (PCR-DGGE) demonstrated that the bacterial community structure in house dust is significantly impacted by the presence of dogs or cats in the home (P ‫؍‬ 0.0190 and 0.0029, respectively) and by whether or not children attend day care (P ‫؍‬ 0.0037). In addition, significant differences in the dust bacterial community were associated with asthma outcomes in young children, including wheezing (P ‫؍‬ 0.0103) and specific IgE (P ‫؍‬ 0.0184). Our findings suggest that specific bacterial populations within the community are associated with either risk or protection from asthma.Recent studies have begun to explore the microbial composition of house dust, finding great diversity and a high abundance of Gram-positive organisms (18,24). Yet this transient community remains relatively unexplored despite increasing evidence of an association between microbial exposure and human health, in particular, the development of chronic diseases such as asthma. Settings with high levels of microbial exposure, such as farms and day care centers, have been associated with protection from asthma (3, 23), while interventions that reduce home microbial exposures have been related to higher rates of allergic sensitization (29). Moreover, variability in home microbial exposures has been linked to differences in immune response and asthma risk in childhood (1, 4). Finally, genes involved in innate immune responses to microbes have been found to interact with microbial exposures, resulting in altered risks for asthma (10). Microbial exposure has primarily been assessed in these studies through measurement of surrogates, such as lipopolysaccharide (LPS, or endotoxin), a component of the outer membrane of Gram-negative bacteria (16), and more recently N-acetyl muramic acid for Gram-positive bacteria (28) and ergosterol for fungi (25). While the use of such surrogates has confirmed a negative relationship between levels of microbial exposure and the development of asthma, exploration is needed beyond a handful of surrogates to more completely represent the complexity of the actual microbial communities present in homes.A preliminary experiment was performed to characterize the bacterial communities of dust from homes in Tucson, AZ. First, general bacterial community diversity was examined in house dust samples by using a PhyloChip microarray as described by Brodie et al. (5). These samples were obtained from homes of four volunteers in the Tucson area. Array results revealed an average of 295 Ϯ 16 (mean Ϯ standard deviation) unique operational taxonomic units (OTUs) per sample, where a taxon was considered present in the sample when more t...

Definition of Biosurfactants and Bioemulsifiers Types of Biosurfactants and Bioemulsifiers Screening for Surfactant and Emulsification Activities Industrial and Biotechnology Applications