Aerobic biodegradation of gasoline oxygenates MTBE and TBA.

MTBE degradation was investigated using a continuously stirred tank reactor (CSTR) with biomass retention (porous pot reactor) operated under aerobic conditions. MTBE was fed to the reactor at an influent concentration of 150 mg/l (1.70 mmol/l). A second identical reactor was operated as a control under the same conditions with the addition of 2.66 g/l of sodium azide, to kill any biological activity. Results from these experiments suggest that biomass retention is critical to the degradation of MTBE. The rate of MTBE removal was shown to be related to the VSS concentration. MTBE removal exceeded 99.99% when the VSS concentration in the reactor was over 600 mg/l. Results obtained from batch experiments conducted on mixed liquor samples from the porous pot reactor indicate that the individual rates of biodegradation of MTBE and TBA were higher for initial concentrations of 15 mg/l than for concentrations of 5 mg/l. The presence of TBA at lower concentrations did not effect the rate of MTBE degradation, however higher concentrations of TBA did reduce the rate of biodegradation of MTBE. Denaturing Gradient Gel Electrophoresis (DGGE) analysis reveals that the culture consisted of a community of bacterial organisms of about 6 species.

Phylogenetic analysis of aerobic freshwater and marine enrichment cultures efficient in hydrocarbon degradation: effect of profiling method.

Aerobically grown enrichment cultures derived from hydrocarbon-contaminated seawater and freshwater sediments were generated by growth on crude oil as sole carbon source. Both cultures displayed a high rate of degradation for a wide range of hydrocarbon compounds. The bacterial species composition of these cultures was investigated by PCR of the 16S rDNA gene using multiple primer combinations. Near full-length 16S rDNA clone libraries were generated and screened by restriction analysis prior to sequence analysis. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was carried out using two other PCR primer sets targeting either the V3 or V6-V8 regions, and sequences derived from prominent DGGE bands were compared to sequences obtained via cloning. All data sets suggested that the seawater culture was dominated by alpha-subgroup proteobacteria, whereas the freshwater culture was dominated by members of the beta- and gamma-proteobacteria. However, the V6-V8 primer pair was deficient in the recovery of Sphingomonas-like 16S rDNA due to a 3' terminal mismatch with the reverse primer. Most 16S rDNA sequences recovered from the marine enrichment were not closely related to genera containing known oil-degrading organisms, although some were detected. All methods suggested that the freshwater enrichment was dominated by genera containing known hydrocarbon-degrading species.

Synaptogenesis in the cerebral hemisphere (accessory hyperstriatum) of the chick embryo.

Axosomatic and axodendritic synapses, containing almost exclusively spherical clear vesicles, were first detected in the embryonic chick hyperstriatal complex at about 10 days of incubation. Axodendritic synapses gradually become more plentiful during the subsequent week in ovo, while axosomatic synapses remain scarce at all stages. An explosive formation of new synapses, all of them packed with spherical clear vesicles, occurs shortly before hatching. This event coincides with rapid maturation of the dendritic branches, especially with respect to spine formation.