Number Of Hydrocarbon Degraders Research Articles

Effect of nickel on the mineralization of hydrocarbons by indigenous microbiota in Kuwait soils

Assessment of nickel contents in soil samples in Kuwait indicated only a minor difference in concentration in hydrocarbon-contaminated (86 mg kg(-1) soil) and non-contaminated soils (84 mg kg(-1) soil). The potential inhibitory effects of nickel on the number of hydrocarbon degraders, and hydrocarbon utilization were investigated over a wide range of nickel concentrations to span concentrations observed in the soil. Nickel addition, as nickel sulphate, to soil samples reduced the number of hydrocarbon degraders in all samples by a wide range (15-96%) depending on concentration and the hydrocarbon substrate utilized. Similarly, the metabolic activities were affected as observed in mineralization (3-60%) of soils amended with various concentrations of nickel. The inhibitive effects of nickel on hexadecane and crude oil utilization were minimal but were significantly higher with naphthalene (P < 0.05) in both hydrocarbon-contaminated and non-contaminated soils. Polarographic determination of hydrocarbons induced oxygen uptake rate demonstrated the tendency of nickel to significantly inhibit (P < 0.05) the oxidation of polyaromatic hydrocarbons compared to aliphatic hydrocarbons.

Phytoremediation of petroleum hydrocarbons in tropical coastal soils II. microbial response to plant roots and contaminant

The goal of this study was to understand the interaction between plants and microorganisms during petroleum-hydrocarbon bioremediation in Pacific Islands coastal soils. Total bacteria and hydrocarbon-degrading microorganisms population dyanamics were examined in the rhizospheres of tropical trees and shrubs, which were evaluated for their phytoremediation potential in a greenhouse experiment. The respective and combined effects of plant roots and diesel contaminant on the microbial populations were determined in relation to diesel fuel depletion. An increase in the grading populations size of the hydrocarbon-degrading populations of microbes, elicited by rhizodeposition, is generally regarded as conducive to an enhanced degradation of petroleum hydrocarbon pollutants in vegetated soil. The soil was a coastal sandy loam (pH 7.8) which was artificially contaminated with 10 g of No. 2 diesel fuel/kg soil or left uncontaminated. The pots were irrigated with fertilizer and 1% NaCl. The enumerations were carried out in the contaminated and uncontaminated rhizospheres of three trees, kiawe (Prosopis pallida), milo (Thespesia populnea), and kou (Cordia subcordata) and three shrubs, beach naupaka (Scaevola sericea), false sandalwood (Myoporum sandwicense), and oleander (Nerium oleander). Unplanted control soils were included in the experiment. Total bacteria and phenanthrene-degrading bacteria were enumerated on plates. Diesel- and pristane-degrading microorganisms were enumerated by the most-probable-number technique in tissue-culture plates. All four types of microorganisms responded to the rhizosphere of the 6 plants in uncontaminated soil and to the diesel contaminant in unplanted soil. In contaminated rhizospheres, no effect of the plant on the hydrocarbon-degrader numbers was visible. Total bacteria responded more to the plant roots than to the contaminant. The phenanthrene-degrading bacteria and pristane-degrading microorganisms were more influenced by the contaminant than by the plants. The diesel-degrading microorganisms were equally stimulated by the plants and the contaminant. The numbers of hydrocarbon degraders were similar in the contaminated rhizospheres of the three effective plants (kiawe, kou, and milo) and in those of the three ineffective shrubs. The results suggest the quality of the rhizodeposition is plant-dependent and governs the type of diesel-degrader populations that will be enhanced by a given plant. In the proposed phytoremediation-benefit model plant roots maintain high levels of hydrocaron degraders in uncontaminated soil. When the root enters a contaminated zone of soil, those hydrocarbon degraders that prefer the contaminant would switch to the contaminant as a carbon source, effectively removing the hydrocarbons. If the root exudates and the contaminant are equally attractive to the hydrocarbon degraders, the contaminant degradaton would be less effective.

Characterization of hydrocarbon-degrading microbial populations in contaminated and pristine Alpine soils.

Biodegradation of petroleum hydrocarbons in cold environments, including Alpine soils, is a result of indigenous cold-adapted microorganisms able to degrade these contaminants. In the present study, the prevalence of seven genotypes involved in the degradation of n-alkanes (Pseudomonas putida GPo1 alkB; Acinetobacter spp. alkM; Rhodococcus spp. alkB1, and Rhodococcus spp. alkB2), aromatic hydrocarbons (P. putida xylE), and polycyclic aromatic hydrocarbons (P. putida ndoB and Mycobacterium sp. strain PYR-1 nidA) was determined in 12 oil-contaminated (428 to 30,644 mg of total petroleum hydrocarbons [TPH]/kg of soil) and 8 pristine Alpine soils from Tyrol (Austria) by PCR hybridization analyses of total soil community DNA, using oligonucleotide primers and DNA probes specific for each genotype. The soils investigated were also analyzed for various physical, chemical, and microbiological parameters, and statistical correlations between all parameters were determined. Genotypes containing genes from gram-negative bacteria (P. putida alkB, xylE, and ndoB and Acinetobacter alkM) were detected to a significantly higher percentage in the contaminated (50 to 75%) than in the pristine (0 to 12.5%) soils, indicating that these organisms had been enriched in soils following contamination. There was a highly significant positive correlation (P < 0.001) between the level of contamination and the number of genotypes containing genes from P. putida and Acinetobacter sp. but no significant correlation between the TPH content and the number of genotypes containing genes from gram-positive bacteria (Rhodococcus alkB1 and alkB2 and Mycobacterium nidA). These genotypes were detected at a high frequency in both contaminated (41.7 to 75%) and pristine (37.5 to 50%) soils, indicating that they are already present in substantial numbers before a contamination event. No correlation was found between the prevalence of hydrocarbon-degradative genotypes and biological activities (respiration, fluorescein diacetate hydrolysis, lipase activity) or numbers of culturable hydrocarbon-degrading soil microorganisms; there also was no correlation between the numbers of hydrocarbon degraders and the contamination level. The measured biological activities showed significant positive correlation with each other, with the organic matter content, and partially with the TPH content and a significant negative correlation with the soil dry-mass content (P < 0.05 to 0.001).

Biodegradation of petroleum hydrocarbons in continental shelf regions of the Bering Sea

Rates of petroleum hydrocarbon biodegradation were measured in water and sediment samples collected from the Bering Sea. Radiolabelled hydrocarbons, hexadecane, pristane, 9-methyl anthracene, and benz(a)anthracene were used to measure most probable numbers of hydrocarbon degraders and biodegradation potentials for various classes of hydrocarbons. Additionally, a six week flow through experiment in the laboratory was conducted to determine biodegradative capacities of sediment microorganisms for alipathic and aromatic components of Cook Inlet crude oil. Results indicated low populations of hydrocarbon degraders in both waters and sediments of the Bering Sea, low mineralization of hydrocarbons, but some modification of the composition of crude oil exposed to the indiginous microorganisms of the Bering Sea. Some differences were observed between ice covered and ice free areas with higher rates of microbial oil degradation associated with ice covered areas. Flow-through experiments demonstrated very low biodegradation of crude oil by sediment microorganisms even when supplied with nutrients. For trajectory modelling purposes our studies indicate that conservation of hydrocarbons must be assumed for at least three weeks, providing sufficient time for oil spilt into the Bering Sea to impact coastal regions.