Crude oil degradation was observed in water samples from three sites along the course of a polluted stream in Lagos, Nigeria. Consistent increase and decrease in the total viable counts (TVCs) of indigenous organisms occurred in the test and control experiments, respectively. Enrichments of the water samples with crude oil resulted in the isolation of nine bacteria belonging to seven genera. A mixed culture was developed from the assemblage of the nine species. The defined microbial consortium utilized a wide range of pure HCs including cycloalkane and aromatic HCs. Utilization of crude oil and petroleum cuts, i.e., kerosene and diesel resulted in an increase in TVC (till day 10) concomitant with decreases in pH and residual oil concentration. Crude oil, diesel and kerosene were degraded by 88, 85 and 78%, respectively, in 14 days. Substrate uptake studies with axenic cultures showed that growth was not sustainable on either cyclohexane or aromatics while degradation of the petroleum fractions fell below 67% in spite of extended incubation period (20 day). From the GC analysis of recovered oil, while reductions in peaks of n-alkane fractions and in biomarkers namely n-C 17 /pristane and n-C 18 / phytane ratios were observed in culture fluids of pure strains, complete removal of all the HC components of kerosene, diesel and crude oil including the isoprenoids was obtained with the consortium within 14 days.

The general toxicity (root growth inhibition and malformation) and genotoxicity (induction of chromosome aberrations in root cells) of an oil field wastewater have been investigated by the Allium test. A series of 10 small bulbs of Allium cepa L. were cultivated in various concentrations of the wastewater, and after 48 h one root tip from each bulb was harvested and processed for cytological studies by the aceto-orcein squash technique. After 96 h, mean lengths of root bundles were obtained and the Effect Concentration (EC) values calculated. Treatment with wastewater resulted in significant dosedependent root growth inhibition. EC,, (96 h) was 28.5 '% while a total phytotoxic effect was induced by the undiluted sample. The wastewater is mitodepressive and increased significantly the frequency of chromosome aberrations in root cells (sticky chromosomes, c-mitosis, spindle multipolarity, bridges and fragments). At lower concentrations c-mitosis was the most common aberration. The suitability of the Allium test in genotoxicity screening is highlighted and the impact and significance of positive results on the environment and human health are discussed.

Pseudomonas sp. strain LP1, an organism isolated on the basis of its ability to grow on pyrene, was assayed for its degradative and biosurfactant production potentials when growing on crude, diesel and engine oils. The isolate exhibited specific growth rate and doubling time of 0.304 days -1 and 2.28 days, respectively on crude oil (Escravos Light). The corresponding values on diesel were 0.233 days -1 and 2.97 days, while on engine oil, were 0.122 days -1 and 5.71 days. The organism did not show significant biosurfactant production towards crude oil and diesel, but readily produced biosurfactant on engine oil. The highest Emulsification index (E 24 ) value for the biosurfactant produced by LP1 on engine oil was 80.33 ± 1.20, on day 8 of incubation. Biosurfactant production was growth-associated. The surface-active compound which exhibited zero saline tolerance had its optimal activity at 50°C and pH 2.0.

Samples of soil, water, and sediments from industrial estates in Lagos were collected and analyzed for heavy metals and physicochemical composition. Bacteria that are resistant to elevated concentrations of metals (Cd(2+), Co(2+), Ni(2+), Cr(6+), and Hg(2+)) were isolated from the samples, and they were further screened for antibiotic sensitivity. The minimum tolerance concentrations (MTCs) of the isolates with dual resistance to the metals were determined. The physicochemistry of all the samples indicated were heavily polluted. Twenty-two of the 270 bacterial strains isolated showed dual resistances to antibiotics and heavy metals. The MTCs of isolates to the metals were 14 mM for Cd(2+), 15 mM for Co(2+) and Ni(2+), 17 mM for Cr(6+), and 10 mM for Hg(2+). Five strains (Pseudomonas aeruginosa, Actinomyces turicensis, Acinetobacter junni, Nocardia sp., and Micrococcus sp.) resisted all the 18 antibiotics tested. Whereas Rhodococcus sp. and Micrococcus sp. resisted 15 mM Ni(2+), P. aeruginosa resisted 10 mM Co(2+). To our knowledge, there has not been any report of bacterial strains resisting such high doses of metals coupled with wide range of antibiotics. Therefore, dual expressions of antibiotics and heavy-metal resistance make the isolates, potential seeds for decommissioning of sites polluted with industrial effluents rich in heavy metals, since the bacteria will be able to withstand in situ antibiosis that may prevail in such ecosystems.

No abstract