Bacterial Degradation of Carbazole and Microbial Diversity of Hydrocarbon-Contaminated Soils in a Tropical Environment.
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Date
2014
Authors
Salam, L.B
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Abstract
Carbazole, an N-heterocyclic aromatic hydrocarbon is of environmental concern due to its persistence, recalcitrance, mutagenic and toxic activities. Degradation of carbazole has been reported since early 1990s, to lead to production of dead-end metabolites and hydroxylated carbazoles, which are released into the environment. However, angular dioxygenation of carbazole reported in very few bacteria genera, with hydroxylation at C1 and C9a carbons produces anthranilic acid and catechol as major metabolites, which are completely mineralized. Four bacterial strains with extensive degradation abilities on carbazole were isolated from three hydrocarbon-contaminated soils (Abandoned Coal Power Plant, ACPP; Mechanic Workshop, MWO and NEPA Substation, UNILAG, NESU) in Lagos, Nigeria. Physicochemical analyses of the soil samples indicate gross pollution of the soils with a high hydrocarbon content (157 g/kg) and presence of heavy metals (lead, nickel, cadmium). Phylogenetic analysis of the four strains indicated that they were Achromobacter sp. strain SL1 (AB646575.2), Pseudomonas sp. strain SL4 (AB646578.2), Microbacterium esteraromaticum strain SL6 (AB646579.2) and Stenotrophomonas maltophilia strain BA (AB646574). The rate of degradation of carbazole by the four isolates, after 30 days of incubation, were 0.057, 0.062, 0.036 and 0.050 mg l-1 h-1 for strains SL1, SL4, SL6 and BA, respectively. Gas chromatographic analyses of residual carbazole, after 30 days of incubation, revealed that 81.3%, 85%, 64.4% and 76% of 50 ppm carbazole were degraded by strains SLI, SL4, SL6 and BA, respectively. GC-MS and HPLC analyses of the extracts from the growing and resting cells of strains SL1, SL4 and SL6 cultured on carbazole revealed anthranilic acid and catechol, which were not detected in strain BA under the same conditions. The three strains (SL1, SL4, SL6) degrade catechol via the ortho pathway producing cis cis muconic acid as established by UV-Vis spectroscopy. Microcosm experiments with sterile and native soils amended with 100 ppm carbazole indicated carbazole removal rates of 66.96%-82.16% in sterile soils and 19.19%-91.64% in native soils by the test organisms. All four strains utilized a wide range of polycyclic and heterocyclic aromatic hydrocarbons. Clone library analysis of 16S rRNA recovered four hundred and thirty seven clones from MWO soil that cut across thirteen different bacterial phyla as revealed by RDP-II and NCBI. The representative bacteria phyla identified from MWO soil, using clone library analysis, were Proteobacteria, Bacteroidetes, Chloroflexi, Acidobacteria, Firmicutes, Actinobacteria, Verrucomicrobia, Planctomycetes, Chlorobi, Spirochaetes, Chlamydiae, TM7 and OD1. The clone library coverage indicates 42% of the library is covered at the species delineation with Shannon index of 5.59. This study has established carbazole angular dioxygenation and mineralization by isolates from a tropical environment. It also revealed the presence of novel bacterial genera contributing to natural attenuation of hydrocarbon pollutants in soil through clone library analysis
Description
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos.
Keywords
Microbial Diversity , Tropical Environment , Bacterial Degradation , Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology::Microbiology
Citation
Salam, L.B (2014), Bacterial Degradation of Carbazole and Microbial Diversity of Hydrocarbon-Contaminated Soils in a Tropical Environment. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 398pp.