RESUMO
A diesel fuel-contaminated aquifer was bioremediated in situ by the injection of oxidants (O2 and NO3-) and nutrients in order to stimulate microbial activity. After 3.5 years of remediation, an aquifer sample was excavated and the material was used (i) to isolate bacterial strains able to grow on selected hydrocarbons under denitrifying conditions and (ii) to construct a laboratory aquifer column in order to simulate the aerobic and denitrifying remediation processes. Five bacterial strains isolated from the aquifer sample were able to grow on toluene (strains T2 to T4, T6, and T10), and nine bacterial strains grew on toluene and m-xylene (strains M3 to M7 and M9 to M12). Strains T2 to T4, T6, and T10 were cocci, and strains M3 to M7 and M9 to M12 were rods. The morphological and physiological differences were also reflected in small sequence variabilities in domain III of the 23S rRNA and in the 16S rRNA. Comparative sequence analyses of the 16S rRNA of one isolate (T3 and M3) of each group revealed a close phylogenetic relationship for both groups of isolates to organisms of the genus Azoarcus. Two 16S rRNA-targeted oligonucleotide probes (Azo644 and Azo1251) targeting the experimental isolates, bacteria of the Azoarcus tolulyticus group, and Azoarcus evansii were used to investigate the significance of hydrocarbon-degrading Azoarcus spp. in the laboratory aquifer column. The number of bacteria in the column determined after DAPI (4',6-diamidino-2-phenylindole) staining was 5.8 x 10(8) to 1.1 x 10(9) cells g of aquifer material-1. About 1% (in the anaerobic zone of the column) to 2% (in the aerobic zone of the column) of these bacteria were detectable by using a combination of probes Azo644 and Azo1251, demonstrating that hydrocarbon-degrading Azoarcus spp. are significant members of the indigenous microbiota. More than 90% of the total number of bacteria were detectable by using probes targeting higher phylogenetic groups. Approximately 80% of these bacteria belonged to the beta subdivision of the class Proteobacteria (beta-Proteobacteria), and 10 to 16% belonged to the gamma-Proteobacteria. Bacteria of the alpha-Proteobacteria were present in high numbers (10%) only in the aerobic zone of the column.
Assuntos
Bactérias/metabolismo , Petróleo/metabolismo , Tolueno/metabolismo , Poluentes Químicos da Água/metabolismo , Xilenos/metabolismo , Bactérias/genética , Bactérias/isolamento & purificação , Sequência de Bases , Biodegradação Ambiental , Primers do DNA/genética , Dados de Sequência Molecular , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , RNA Ribossômico 23S/genética , Homologia de Sequência do Ácido Nucleico , Microbiologia da ÁguaRESUMO
Evidence shows the presence on the chromosome of Methanobacterium wolfei of a defective prophage which, by DNA-DNA hybridization, is closely related to the virulent archaeophage psi M1 of Methanobacterium thermoautotrophicum Marburg. Partial sequencing of a M. wolfei 16S rRNA gene and phylogenetic analysis indicated that this organism is more closely related to other representatives of the genus Methanobacterium than to M. thermoautotrophicum Marburg. The chromosomal region of M. wolfei encoding the putative prophage was found to be deleted for two non-contiguous segments of the phage psi M1 genome and thus encompassed only 80 to 90% of the psi M1 DNA. The prophage region was mapped to a 30 kb restriction fragment on the physical map of the M. wolfei chromosome. A randomly chosen DNA fragment was cloned from phage psi M1 DNA, as was its homologous counterpart from the chromosome of M. wolfei. The 126-bp region present in both clones exhibited 100% sequence identity.
Assuntos
Bacteriófagos/genética , Cromossomos Bacterianos , Methanobacterium/virologia , DNA Viral/química , Evolução Molecular , Methanobacterium/genética , Dados de Sequência Molecular , Filogenia , RNA Bacteriano/química , RNA Ribossômico 16S/química , Mapeamento por Restrição , Análise de Sequência de DNARESUMO
Two adjacent genes in Bradyrhizobium japonicum, fbcF and fbcH, encode the Rieske iron sulfur protein and cytochromes b and c1, characteristic constituents of the respiratory complex III. Remarkably, fbcH is a single gene of which the 5' half codes for cytochrome b and the 3' half codes for cytochrome c1. Experimental evidence suggests that a large FbcH precursor is posttranslationally processed into the two proteins. B. japonicum fbcF and fbcH insertion mutants grow aerobically but are unable to fix nitrogen in root nodule symbiosis with soybean. Thus, fbcF and fbcH are symbiotically essential. We propose that B. japonicum makes use of a cytochrome bc1-containing respiratory chain on its way to become a microaerobic endosymbiont, whereas under aerobiosis, respiration can occur by a bc1-independent pathway.
