Olukayode O. Amund

Extensive biodegradation of polychlorinated biphenyls in Aroclor 1242 and electrical transformer fluid (Askarel) by natural strains of microorganisms indigenous to contaminated African systems

Evidence for substantial aerobic degradation of Aroclor 1242 and Askarel fluid by newly characterized bacterial strains belonging to the Enterobacter, Ralstonia and Pseudomonas genera is presented. The organisms exhibited degradative activity in terms of total PCB/Askarel degradation, degradation of individual congeners and diversity of congeners attacked. Maximal degradation by the various isolates of Askarel ranged from 69% to 86% whereas, Aroclor 1242, with the exception of Ralstonia sp. SA-4 (9.7%), was degraded by 37% to 91%. PCB analysis showed that at least 45 of the representative congeners in Aroclor 1242 were extensively transformed by benzoate-grown cells without the need for biphenyl as an inducer of the upper degradation pathway. In incubations with Aroclor 1242, no clear correlation was observed between percentage of congener transformed and the degree of chlorination, regardless of the presence or absence of biphenyl. Recovery of significant but nonstoichiometric amounts of chloride from the culture media showed partial dechlorination of congeners and suggested production of partial degradation products. Addition of biphenyl evidently enhanced dechlorination of the mixture by some isolates. With the exception of Ralstonia sp. SA-5, chloride released ranged from 24% to 60% in the presence of biphenyl versus 0.35% to 15% without biphenyl.

Microbial population changes in tropical agricultural soil experimentally contaminated with crude petroleum

Impacts of crude petroleum pollution on the soil environment and microbial population dynamics as well as recovery rates of an abandoned farmland was monitored for seven months spanning the two major seasons in Nigeria with a view to establishing process conditions necessary for development of effective strategies for bioremediation. The physico-chemistry of the control and contaminated soils differed just significantly (P soil showed significant diversity in structure and number of flora .There was an initial drop in microbial population densities at the onset of pollution but, a gradual increase was observed thereafter. Higher counts of microflora were obtained for April, May, June and July samples which coincided with the onset and peak of wet season. A rapid and significant reduction in residual oil concentration was observed during this period. Overall, nearly 100% of the crude oil pollutant was degraded within the 28-week study period. The residual oil concentration gave a high but negative correlation coefficient (r = - 0.84 to -0.90) with total heterotrophic and hydrocarbon-utilizing populations. On application of data generated to model equations, approximately 60.5 weeks would elapse before the contaminated soil could recover from the impact of the oil. Our results show that a natural population readily able to degrade crude oil is present in the soil chosen for this study. However, it may be necessary to monitor the level of inorganic nutrients and adjust some appropriately to enhance biodegradation of the organic pollutant.

Biodegradation of petroleum hydrocarbons in the presence of nickel and cobalt.

Bioremediation of environments co‐contaminated with hydrocarbons and heavy metals often pose a challenge as heavy metals exert toxicity to existing communities of hydrocarbon degraders. Multi‐resistant bacterial strains were studied for ability to degrade hydrocarbons in chemically defined media amended with 5.0 mM Ni2+, and Co2+. The bacteria, Pseudomonas aeruginosa CA207Ni, Burkholderia cepacia AL96Co, and Corynebacterium kutscheri FL108Hg, utilized crude oil and anthracene without lag phase at specific growth rate spanning 0.3848–0.8259 per day. The bacterial populations grew in hydrocarbon media amended with nickel (Ni) and cobalt (Co) at 0.8393–1.801 days generation time (period of exponential growth, t = 15 days). The bacteria degraded 96.24–98.97, and 92.94–96.24% of crude oil, and anthracene, respectively, within 30 days without any impedance due to metal toxicity (at 5.0 mM). Rather, there was reduction of Ni and Co concentrations in the axenic culture 30 days post‐inoculation to 0.08–0.12 and 0.11–0.15 mM, respectively. The metabolic functions of the bacteria are active in the presence of toxic metals (Ni and Co) while utilizing petroleum hydrocarbons for increase in biomass. These findings are useful to other baseline studies on decommissioning of sites co‐contaminated with hydrocarbons and toxic metals.

Extracellular amylase production by cassava-fermenting bacteria

SummaryFermentation of cassava tubers was accompanied by a gradual decrease in pH, increased amylase activity in the steep liquor, and increased microbial load and lactic acid concentration. Amylase-producing bacterial strains associated with cassava fermentation were isolated and identified asBacillus subtilis, Bacillus licheniformis andBacillus cereus. The pH optima for the partially purified enzymes of these organisms were 7.0, 5.5 and 7.5, whilst their temperature optima were 30, 37 and 80°C. There was no significant difference in amylase activities when starch, dextrin, amylopectin, glucose and maltose were used as growth substrates.

Purification and properties of an α-amylase produced by a cassava-fermenting strain ofMicrococcus luteus

An extracellular α-amylase produced by a cassava-fermenting strain ofMicrococcus luteus was purified 26-fold by gel filtration and ion-exchange chromatography. The molar mass was estimated to be approximately 56 kDa. The optimum temperature of the enzyme was 30°C, optimum pH 6.0 and optimum substrate concentration was 0.6% (W/V). Treatment of the enzyme at 70°C for 10 min resulted in 70% loss of activity. The activation energy was determined to be 34.8 kJ/mol. The activity of the enzyme was enhanced by Mg2+, Ca2+, K+, Na+ and inhibited by EDTA, KCN and citric acid. The enzyme may find some application in local food processing.

Utilization and degradation of an ester-based synthetic lubricant by Acinetobacter lwoffi

An oil-degrading bacterium, Acinetobacter lwoffi, isolated by elective culture from the Medway estuary, utilized an ester-based synthetic lubricating oil EMKARATE DE 155 as sole carbon and energy source. Analysis of culture supernatants by gas chromatography showed the accumulation of a nondegradable metabolite 1,1,1 Tris (hydroxymethyl) propane in addition to two metabolizable fatty acids, octanoic and decanoic acids as products of the synthetic oil degradation. Esterase activities were subsequently demonstrated in oil and acetate-grown cells. The synthetic oil therefore appears to be partially biodegradable in the environment.

Microbial Communities in Sediments of Lagos Lagoon, Nigeria: Elucidation of Community Structure and Potential Impacts of Contamination by Municipal and Industrial Wastes.

Estuarine sediments are significant repositories of anthropogenic contaminants, and thus knowledge of the impacts of pollution upon microbial communities in these environments is important to understand potential effects on estuaries as a whole. The Lagos lagoon (Nigeria) is one of Africa’s largest estuarine ecosystems, and is impacted by hydrocarbon pollutants and other industrial and municipal wastes. The goal of this study was to elucidate microbial community structure in Lagos lagoon sediments to identify groups that may be adversely affected by pollution, and those that may serve as degraders of environmental contaminants, especially polycyclic aromatic hydrocarbons (PAHs). Sediment samples were collected from sites that ranged in types and levels of anthropogenic impacts. The sediments were characterized for a range of physicochemical properties, and microbial community structure was determined by Illumina sequencing of the 16S rRNA genes. Microbial diversity (species richness and evenness) in the Apapa and Eledu sediments was reduced compared to that of the Ofin site, and communities of both of the former two were dominated by a single operational taxonomic unit (OTU) assigned to the family Helicobacteraceae (Epsilonproteobacteria). In the Ofin community, Epsilonproteobacteria were minor constituents, while the major groups were Cyanobacteria, Bacteroidetes, and Firmicutes, which were all minor in the Apapa and Eledu sediments. Sediment oxygen demand (SOD), a broad indicator of contamination, was identified by multivariate analyses as strongly correlated with variation in alpha diversity. Environmental variables that explained beta diversity patterns included SOD, as well as levels of naphthalene, acenaphthylene, cobalt, cadmium, total organic matter, or nitrate. Of 582 OTU identified, abundance of 167 was significantly correlated (false discovery rate q≤ 0.05) to environmental variables. The largest group of OTU correlated with PAH levels were PAH/hydrocarbon-degrading genera of the Oceanospirillales order (Gammaproteobacteria), which were most abundant in the hydrocarbon-contaminated Apapa sediment. Similar Oceanospirillales taxa are responsive to marine oil spills and thus may present a unifying theme in marine microbiology as bacteria adapted for degradation of high hydrocarbon loads, and may represent a potential means for intrinsic remediation in the case of the Lagos lagoon sediments.

Extensive Biodegradation of Nigerian Crude Oil (Escravos Light) by Newly Characterized Yeast Strains

Abstract Because microbial degradation is known to be an efficient process in the in situ decontamination of oil-bearing environments, it is believed that development of effective bioremediation strategies will be aided by microbial sourcing of novel and competent hydrocarbon degraders with a broad and unusual substrate spectrum. Thus, in keeping with this objective, two Candida strains (MN1 and MC1) isolated after a repeated batch enrichment technique were tested for their biodegradation potentials on Nigerian crude oil, Escravos light. Axenic cultures of strains MN1 and MC1 grew at a rate of 1.623 and 0.586 d−1, respectively, in mineral salts medium supplemented with 8.4 g L−1 of crude oil. Whereas strain MN1 degraded aliphatic fractions by 97.6% and the aromatics by 74.61%, the corresponding values obtained for MC1 were 97.2% and 67.29% during the 14-day incubation period. The gas chromatography (GC) fingerprinting of aliphatic fractions showed major degradation of heptadecane (C17), octadecane (C18), nonadecane (C19), eicosane (C20), undodecane (C21), tricosane (C23), hexacosane (C26), octacosane (C28), and nonacosane (C29) in less than 6 days, whereas nearly 100% of these fractions including the isoprenoid molecules was metabolized in 14 days. Among the aromatic fractions that were nearly eliminated during the cultivation period were naphthalene, phenanthrene, fluoranthrene, chrysene, benzo(a)anthracene, benzo(b)fluoranthrene, and benzo(a)pyrene. Interestingly, substrate uptake studies showed that both strains grew very well on petroleum cuts, biphenyl, phenol, xylene, and quite a number of polycyclic aromatic hydrocarbons including pyrene, phenanthrene, and anthracene.

Metabolism of Atrazine in Liquid Cultures and Soil Microcosms by Nocardioides Strains Isolated from a Contaminated Nigerian Agricultural Soil

Atrazine-degrading microorganisms designated EAA-3 and EAA-4, belonging to the genus Nocardioides, were obtained from an agricultural soil in Nigeria. The degradation kinetics of the two strains revealed total disappearance of 25 mg l−1 of atrazine in less than 72 h of incubation at the rate of 0.42 mg l−1 h−1 and 0.35 mg l−1 h−1, respectively. Screening for atrazine catabolic genes in these organisms revealed the presence of trzN, atzB, and atzC. Other genes, specifically atzA, atzD, and trzD, were not detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy, while desisopropyl desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine were attacked but in the presence of glucose. A soil microcosm study showed that degradation was faster in microcosms contaminated with 13 mg of atrazine per g−1 of soil compared with 480 mg g−1 of soil. In the former, degradation was 10% higher in the inoculated soil than the non-inoculated control (natural attenuation) over the 28-day study period. Corresponding value obtained for the latter was nearly 70% higher. This study has demonstrated that the bacterial strains isolated enhanced atrazine degradation and the catabolic activities of these strains were not affected with increasing soil atrazine concentration.

Degradation of commercial detergent products by microbial populations of the Lagos lagoon

The biodegradability potentials of three detergent products with the trade names Omo, Teepol and sodium dodecyl sulfate (SDS) by the native bacteria of the Lagos lagoon was carried out using the lagoon die-away method. Physicochemical parameters of the water samples showed that the lagoon in Apapa was more polluted than at theUniversity of Lagos. In 12 days, approximately 30, 60 and 97% of Omo, Teepol and SDS respectively were degraded. SDS with an alkyl sulfate moiety as surfactant supported the highest growth of the detergent-utilizing organisms, indicating that the components of Omo and Teepol are more resistant to microbial attack. The detergent-utilizing bacteria identified were mainly Gram-negative and of the following genera:Vibrio, Klebsiella, Flavobacterium, Pseudomonas, Escherichia, Enterobacter, Proteus, Shigella andCitrobacter. Vibrio was the most frequently encountered organism whileProteus was the rarest. Results of this investigation had shown that detergents made in Nigeria may still contain components that are recalcitrant to biodegradation.