In order to enhance the utilization of inorganic nanoparticles in biological systems, it is important to develop a fundamental understanding of the influence they have on cellular health and function. Experiments were conducted to test silica, silica/iron oxide, and gold nanoparticles for their effects on the growth and activity of Escherichia coli (E. coli). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the morphology and quantify size distribution of the nanoparticles, respectively. TEM was also used to verify the interactions between composite iron oxide nanoparticles and E. coli. The results from DLS indicated that the inorganic nanoparticles formed small aggregates in the growth media. Growth studies measured the influence of the nanoparticles on cell proliferation at various concentrations, showing that the growth of E. coli in media containing the nanoparticles indicated no overt signs of toxicity.

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Baltimore Harbor (Baltimore, MD) sediments were utilized to initiate anaerobic enrichment cultures with polycyclic aromatic hydrocarbons (PAHs) in the absence of supplementary electron acceptors. Cultures amended with naphthalene and phenanthrene exhibited sustained, transferable degradation of the PAHs. Bromoethanesulfonic acid, a selective inhibitor of methanogenesis, inhibited the degradation of 200 microM: naphthalene and phenanthrene; molecular characterization based on 16S rRNA sequences confirmed that methanogenic Archaea were eliminated, thus providing evidence that methanogenesis is involved in the degradation pathway.

Previous research demonstrated that methanogenic cultures enriched from Baltimore Harbor (Baltimore, MD) sediments were able to degrade naphthalene and phenanthrene. In this report, the degradation activity was maintained through a sequential transfer without adding additional sediments and the established polycyclic aromatic hydrocarbon (PAH)-degrading methanogenic communities were characterized via comparative sequence analysis of clone libraries of 16S rRNA genes amplified using bacteria-specific and Archaea-specific primers. The phylogenetic analysis indicated that the addition of PAHs clearly shifted the structure of the methanogenic community and resulted in an increase in populations of species previously found in other hydrocarbon-degrading communities. Of particular interest is the fact that the dominant microbial population of the naphthalene cultures was different from that of the phenanthrene cultures, suggesting that different species are involved in the degradation. Finally, this information may lead to the identification and isolation of methanogenic populations that can degrade PAHs.

Defined microbial communities were developed by combining selective enrichment with molecular monitoring of total community genes coding for 16S rRNAs (16S rDNAs) to identify potential polychlorinated biphenyl (PCB)-dechlorinating anaerobes that orthodechlorinate 2,3,5,6-tetrachlorobiphenyl. In enrichment cultures that contained a defined estuarine medium, three fatty acids, and sterile sediment, a Clostridium sp. was predominant in the absence of added PCB, but undescribed species in the δ subgroup of the class Proteobacteria, the low-G+C gram-positive subgroup, the Thermotogales subgroup, and a single species with sequence similarity to the deeply branching speciesDehalococcoides ethenogenes were more predominant during active dechlorination of the PCB. Species with high sequence similarities to Methanomicrobiales andMethanosarcinales archaeal subgroups were predominant in both dechlorinating and nondechlorinating enrichment cultures. Deletion of sediment from PCB-dechlorinating enrichment cultures reduced the rate of dechlorination and the diversity of the community. Substitution of sodium acetate for the mixture of three fatty acids increased the rate of dechlorination, further reduced the community diversity, and caused a shift in the predominant species that included restriction fragment length polymorphism patterns not previously detected. Although PCB-dechlorinating cultures were methanogenic, inhibition of methanogenesis and elimination of the archaeal community by addition of bromoethanesulfonic acid only slightly inhibited dechlorination, indicating that the archaea were not required for ortho dechlorination of the congener. Deletion of Clostridium spp. from the community profile by addition of vancomycin only slightly reduced dechlorination. However, addition of sodium molybdate, an inhibitor of sulfate reduction, inhibited dechlorination and deleted selected species from the community profiles of the class Bacteria. With the exception of one 16S rDNA sequence that had the highest sequence similarity to the obligate perchloroethylene-dechlorinating Dehalococcoides, the 16S rDNA sequences associated with PCB ortho dechlorination had high sequence similarities to the δ, low-G+C gram-positive, andThermotogales subgroups, which all include sulfur-, sulfate-, and/or iron(III)-respiring bacterial species.