Life at the energetic edge: kinetics of circumneutral iron oxidation by lithotrophic iron-oxidizing bacteria isolated from the wetland-plant rhizosphere

Batch cultures of a lithotrophic Fe(II)-oxidizing bacterium, strain BrT, isolated from the rhizosphere of a wetland plant, were grown in bioreactors and used to determine the significance of microbial Fe(II) oxidation at circumneutral pH and to identify abiotic variables that affect the partitioning between microbial oxidation and chemical oxidation. Strain BrT grew only in the presence of an Fe(II) source, with an average doubling time of 25 h. In one set of experiments, Fe(II) oxidation rates were measured before and after the cells were poisoned with sodium azide. These experiments indicated that strain BrT accounted for 18 to 53% of the total iron oxidation, and the average cellular growth yield was 0.70 g of CH2O per mol of Fe(II) oxidized. In a second set of experiments, Fe(II) was constantly added to bioreactors inoculated with live cells, killed cells, or no cells. A statistical model fitted to the experimental data demonstrated that metabolic Fe(II) oxidation accounted for up to 62% of the total oxidation. The total Fe(II) oxidation rates in these experiments were strongly limited by the rate of Fe(II) delivery to the system and were also influenced by O2 and total iron concentrations. Additionally, the model suggested that the microbes inhibited rates of abiotic Fe(II) oxidation, perhaps by binding Fe(II) to bacterial exopolymers. The net effect of strain BrT was to accelerate total oxidation rates by up to 18% compared to rates obtained with cell-free treatments. The results suggest that neutrophilic Fe(II)-oxidizing bacteria may compete for limited O2 in the rhizosphere and therefore influence other wetland biogeochemical cycles.     

Human T cell responses to the Epstein-Barr nuclear antigen-1 (EBNA-1) as evaluated by synthetic peptides

A panel of synthetic peptides derived from Epstein-Barr virus (EBV) nuclear antigen 1 (EB-NA-1) was used to examine human T cell responses to this antigen. In six of seven normal persons with past EBV infection, T cell precursors specific for five peptides (P27, amino acid residues 83-101;P62, 148-166;E31, 353-367;E41, 368-381; and E11, 461-474) were detectable. The precursor frequencies were in the range of 1:20,000 to less than 1:100,000 peripheral blood mononuclear cells as determined by limiting dilution analyses. Only two of these peptides were predicted as alpha-helices; all peptides were glycine-rich. Four other peptides were not reactive in the seven individuals tested. T cell responses were not detectable in donors without prior EBV infection. Infectious mononucleosis patients investigated 4-6 weeks after diagnosis had likewise no detectable peptide-specific T cell precursors. Thus, it appears that T cells recognizing peptides from EBNA-1 arise and persist in people with past EBV infection.     

Discrimination of multiple Dehalococcoides strains in a trichloroethene enrichment by quantification of their reductive dehalogenase genes

While many anaerobic microbial communities are capable of reductively dechlorinating tetrachloroethene (PCE) and trichloroethene (TCE) to dichloroethene (DCE), vinyl chloride (VC), and finally ethene, the accumulation of the highly toxic intermediates, cis-DCE (cDCE) and VC, presents a challenge for bioremediation processes. Members of the genus Dehalococcoides are apparently solely responsible for dechlorination beyond DCE, but isolates of Dehalococcoides each metabolize only a subset of PCE dechlorination intermediates and the interactions among distinct Dehalococcoides strains that result in complete dechlorination are not well understood. Here we apply quantitative PCR to 16S rRNA and reductase gene sequences to discriminate and track Dehalococcoides strains in a TCE enrichment derived from soil taken from the Alameda Naval Air Station (ANAS) using a four-gene plasmid standard. This standard increased experimental accuracy such that 16S rRNA and summed reductase gene copy numbers matched to within 10%. The ANAS culture was found to contain only a single Dehalococcoides 16S rRNA gene sequence, matching that of D. ethenogenes 195, but both the vcrA and tceA reductive dehalogenase genes. Quantities of these two genes in the enrichment summed to the quantity of the Dehalococcoides 16S rRNA gene. Further, between ANAS subcultures enriched on TCE, cDCE, or VC, the relative copy number of the two dehalogenases shifted 14-fold, indicating that the genes are present in two different Dehalococcoides strains. Comparison of cell yields in VC-, cDCE-, and TCE-enriched subcultures suggests that the tceA-containing strain is responsible for nearly all of the TCE and cDCE metabolism in ANAS, whereas the vcrA-containing strain is responsible for all of the VC metabolism.