Indigenous hydrocarbon-utilizing bacterioflora in oil-polluted habitats in Kuwait, two decades after the greatest man-made oil spill.

Kuwaiti habitats with two-decade history of oil pollution were surveyed for their inhabitant oil-utilizing bacterioflora. Seawater samples from six sites along the Kuwaiti coasts of the Arabian Gulf and desert soil samples collected from seven sites all over the country harbored oil-utilizing bacteria whose numbers made up 0.0001-0.01% of the total, direct, microscopic counts. The indigenous bacterioflora in various sites were affiliated to many species. This was true when counting was made on nitrogen-containing and nitrogen-free media. Seawater samples harbored species belonging predominantly to the Gammaproteobacteria and desert soil samples contained predominantly Actinobacteria. Bacterial species that grew on the nitrogen-free medium and that represented a considerable proportion of the total in all individual bacterial consortia were diazotrophic. They gave positive acetylene-reduction test and possessed the nifH genes in their genomes. Individual representative species could utilize a wide range of aliphatic and aromatic hydrocarbons, as sole sources of carbon and energy. Quantitative determination showed that the individual species consumed crude oil, n-octadecane and phenanthrene, in batch cultures. It was concluded that the indigenous microflora could be involved in bioremediation programs without bioaugmentation or nitrogen fertilization. Irrigation would be the most important practice in bioremediation of the polluted soil desert areas.

Phytoremediation of mercury in pristine and crude oil contaminated soils: Contributions of rhizobacteria and their host plants to mercury removal.

The rhizospheric soils of three tested legume crops: broad beans (Vicia faba), beans (Phaseolus vulgaris) and pea (Pisum sativum), and two nonlegume crops: cucumber (Cucumis sativus) and tomato, (Lycopersicon esculentum) contained considerable numbers (the magnitude of 10(5)g(-1) soil) of bacteria with the combined potential for hydrocarbon-utilization and mercury-resistance. Sequencing of the 16S rRNA coding genes of rhizobacteria associated with broad beans revealed that they were affiliated to Citrobacter freundii, Enterobacter aerogenes, Exiquobacterium aurantiacum, Pseudomonas veronii, Micrococcus luteus, Brevibacillus brevis, Arthrobacter sp. and Flavobacterium psychrophilum. These rhizobacteria were also diazotrophic, i.e. capable of N(2) fixation, which makes them self-sufficient regarding their nitrogen nutrition and thus suitable remediation agents in nitrogen-poor soils, such as the oily desert soil. The crude oil attenuation potential of the individual rhizobacteria was inhibited by HgCl(2), but about 50% or more of this potential was still maintained in the presence of up to 40 mgl(-1) HgCl(2). Rhizobacteria-free plants removed amounts of mercury from the surrounding media almost equivalent to those removed by the rhizospheric bacterial consortia in the absence of the plants. It was concluded that both the collector plants and their rhizospheric bacterial consortia contributed equivalently to mercury removal from soil.

Biodegradation of crude oil and pure hydrocarbons by extreme halophilic archaea from hypersaline coasts of the Arabian Gulf.

Two extreme halophilic Haloferax strains and one strain each of Halobacterium and Halococcus were isolated from a hypersaline coastal area of the Arabian Gulf on a mineral salt medium with crude oil vapor as a sole source of carbon and energy. These archaea needed at least 1 M NaCl for growth in culture, and grew best in the presence of 4 M NaCl or more. Optimum growth temperatures lied between 40 and 45 degrees C. The four archaea were resistant to the antibiotics chloramphenicol, cycloheximide, nalidixic acid, penicillin, streptomycin and tetracycline. The strains could grow on a wide scope of aliphatic and aromatic (both mono-and polynuclear) hydrocarbons, as sole sources of carbon and energy. Quantitative measurements revealed that these extreme halophilic prokaryotes could biodegrade crude oil (13-47%, depending on the strain and medium salinity), n-octadecane (28-67%) and phenanthrene (13-30%) in culture after 3 weeks of incubation. The rates of biodegradation by all strains were enhanced with increasing NaCl concentration in the medium. Optimal concentration was 3 M NaCl, but even with 4 M NaCl the hydrocarbon-biodegradation rates were higher than with 1 and 2 M NaCl. It was concluded that these archaea could contribute to self-cleaning and bioremediation of oil-polluted hypersaline environments.