Moderately thermophilic, hydrocarbonoclastic bacterial communities in Kuwaiti desert soil: enhanced activity via Ca(2+) and dipicolinic acid amendment.

Pristine and oil-contaminated desert soil samples from Kuwait harbored between 10 and 100 cells g(-1) of hydrocarbonoclastic bacteria capable of growth at 50 °C. Enrichment by incubation of moistened soils for 6 months at 50 °C raised those numbers to the magnitude of 10(3) cells g(-1). Most of these organisms were moderately thermophilic and belonged to the genus Bacillus; they grew at 40-50 °C better than at 30 °C. Species belonging to the genera Amycolatopsis, Chelativorans, Isoptericola, Nocardia, Aeribacillus, Aneurinibacillus, Brevibacillus, Geobacillus, Kocuria, Marinobacter and Paenibacillus were also found. This microbial diversity indicates a good potential for hydrocarbon removal in soil at high temperature. Analysis of the same desert soil samples by a culture-independent method (combined, DGGE and 16S rDNA sequencing) revealed dramatically different lists of microorganisms, many of which had been recorded as hydrocarbonoclastic. Many species were more frequent in the oil contaminated than in the pristine soil samples, which may reflect their hydrocarbonoclastic activity in situ. The growth and hydrocarbon consumption potential of all tested isolates were dramatically enhanced by amendment of the cultures with Ca(2+) (up to 2.5 M CaSO4). This enhanced effect was even amplified when in addition 8 % w/v dipicolinic acid was amended. These novel findings are useful in suggesting biotechnologies for waste hydrocarbon remediation at moderately high temperature.

Hydrocarbonoclastic biofilms based on sewage microorganisms and their application in hydrocarbon removal in liquid wastes.

Attempts to establish hydrocarbonoclastic biofilms that could be applied in waste-hydrocarbon removal are still very rare. In this work, biofilms containing hydrocarbonoclastic bacteria were successfully established on glass slides by submerging them in oil-free and oil-containing sewage effluent for 1 month. Culture-dependent analysis of hydrocarbonoclastic bacterial communities in the biofilms revealed the occurrence of the genera Pseudomonas, Microvirga, Stenotrophomonas, Mycobacterium, Bosea, and Ancylobacter. Biofilms established in oil-containing effluent contained more hydrocarbonoclastic bacteria than those established in oil-free effluent, and both biofilms had dramatically different bacterial composition. Culture-independent analysis of the bacterial flora revealed a bacterial community structure totally different from that determined by the culture-dependent method. In microcosm experiments, these biofilms, when used as inocula, removed between 20% and 65% crude oil, n-hexadecane, and phenanthrene from the surrounding effluent in 2 weeks, depending on the biofilm type, the hydrocarbon identity, and the culture conditions. More of the hydrocarbons were removed by biofilms established in oil-containing effluent than by those established in oil-free effluent, and by cultures incubated in the light than by those incubated in the dark. Meanwhile, the bacterial numbers and diversities were enhanced in the biofilms that had been previously used in hydrocarbon bioremediation. These novel findings pave a new way for biofilm-based hydrocarbon bioremediation, both in sewage effluent and in other liquid wastes.

Bioremediation of oily hypersaline soil and water via potassium and magnesium amendment.

Ten hydrocarbonoclastic halobacterial species and 5 haloarchaeal species that had been isolated on a mineral medium with oil as the sole carbon source grew better and consumed more crude oil, as measured by gas-liquid chromatography, in media receiving between 0.50 and 0.75 mol/L KCl and between 1.50 and 2.25 mol/L MgSO4. Chemical analysis revealed that within a certain limit, the higher the KCl and MgSO4 concentrations in the medium, the more K⁺ and Mg²âº, respectively, was accumulated by cells of all the tested halobacteria and haloarchaea. Also, in experiments in which total natural microbial consortia in hypersaline soil and water samples were directly used as inocula, the consumption of hydrocarbons was enhanced in the presence of the above given concentrations of KCl and MgSO4. It was concluded that amendment with calculated concentrations of K⁺ and Mg²âº could be a promising practice for hydrocarbon bioremediation in hypersaline environments.

Oil-bioremediation potential of two hydrocarbonoclastic, diazotrophic Marinobacter strains from hypersaline areas along the Arabian Gulf coasts.

Two halophilic, hydrocarbonoclastics bacteria, Marinobacter sedimentarum and M. flavimaris, with diazotrophic potential occured in hypersaline waters and soils in southern and northern coasts of Kuwait. Their numbers were in the magnitude of 10(3) colony forming units g(-1). The ambient salinity in the hypersaline environments was between 3.2 and 3.5 M NaCl. The partial 16S rRNA gene sequences of the two strains showed, respectively, 99 and 100% similarities to the sequences in the GenBank. The two strains failed to grow in the absence of NaCl, exhibited best growth and hydrocarbon biodegradation in the presence of 1 to 1.5 M NaCl, and still grew and maintained their hydrocarbonoclastic activity at salinities up to 5 M NaCl. Both species utilized Tween 80, a wide range of individual aliphatic hydrocarbons (C9-C40) and the aromatics benzene, biphenyl, phenanthrene, anthracene and naphthalene as sole sources of carbon and energy. Experimental evidence was provided for their nitrogen-fixation potential. The two halophilic Marinobacter strains successfully mineralized crude oil in nutrient media as well as in hypersaline soil and water microcosms without the use of any nitrogen fertilizers.

Enhanced haloarchaeal oil removal in hypersaline environments via organic nitrogen fertilization and illumination.

Hypersaline soil and pond water samples were mixed with 3 % crude oil, some samples were autoclaved to serve as sterile controls; experimental samples were not sterilized. After 6-week incubation at 40 °C under light/dark cycles, the soil microflora consumed 66 %, and after 4 weeks the pond water microflora consumed 63 % of the crude oil. Soil samples treated with 3 % casaminoacids lost 89 % of their oil after 6 weeks and water samples lost 86 % after 4 weeks. Samples treated with casaminoacids and antibiotics that selectively inhibited bacteria, lost even more oil, up to 94 %. Soil-water mixtures incubated under continuous illumination lost double as much more oil than samples incubated in the dark. The soil-water mixture at time zero contained 1.3 × 10(4) CFU g(-1) of hydrocarbon-utilizing microorganisms which were affiliated to Halomonas aquamarina, Exiguobacterium aurantiacum, Haloferax sp., Salinococcus sp., Marinococcus sp. and Halomonas sp. After 6-week incubation with oil, these numbers were 8.7 × 10(7) CFU g(-1) and the Haloferax sp. proportion in the total microflora increased from 20 to 93 %. Experiments using the individual cultures and three other haloarchaea isolated earlier from the same site confirmed that casaminoacids and light enhanced their oil consumption potential in batch cultures.

Mercury resistance and volatilization by oil utilizing haloarchaea under hypersaline conditions.

The hydrocarbon utilizing haloarchaea, Haloferax (two strains), Halobacterium and Halococcus from a hypersaline coastal area of the Arabian Gulf, had the potential for resistance and volatilization of Hg(2+). Individual haloarchaea resisted up to between 100 and 200 ppm HgCl2 in hydrocarbon free media with salinities between 1 and 4 M NaCl, but only up to between 20 and 30 ppm in a mineral medium containing 3 M NaCl, with 0.5% (w/v) crude oil, as a sole source of carbon and energy. Halococcus and Halobacterium volatilized more mercury than Haloferax. The individual haloarchaea consumed more crude oil in the presence of 3 M NaCl than in the presence of 2 M NaCl. At both salinities, increasing the HgCl2 concentration in the medium from 0 to 20 ppm resulted in decreasing the oil consumption values by the individual haloarchaea. However, satisfactory oil consumption still occurred in the presence of 10 ppm HgCl2. It was concluded that haloarchaea with the combined potential for mercury resistance and volatilization and hydrocarbon consumption could be useful in removing toxic mercury forms effectively from oil free, mercury contaminated, hypersaline environments, and mercury and oil, albeit less effectively, from oily hypersaline environments.

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.