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PubMed2002

Occurrence of crude oil degrading bacteria in gasoline and diesel station soils.

Microbial enumeration and identification were carried out on several oil contaminated soil samples collected from gasoline and diesel stations. Bacteria were the most dominant microbiota and were therefore classified to generic level. Eleven main genera were detected and Corynebacterium was the predominant genus in all the samples. Biochemical characterisation and substrate utilisation showed high percentage of lipolytic ability combined with high inorganic nitrogen utilisers. The ability of these cultures to degrade crude oil was tested individually and in mixed bacterial consortium at different temperatures and pH values. Maximum crude oil biodegradation of 78% was achieved using a bacterial consortium containing five cultures (Micrococcus sp. GS2-22, Corynebacterium sp. GS5-66, Flavobacterium sp. DS5-73, Bacillus sp. DS6-86 and Pseudomonas sp. DS10-129) with 1% crude oil at 30 degrees C and pH 7.5. Such a consortium may be useful for bioaugmentation of oil contaminated environments.

Bacteria↗
PubMed2002

Isolation and characterization of bacteria from crude petroleum oil contaminated soil and their potential to degrade diesel fuel.

Potential hydrocarbon degrader bacteria were isolated from soil samples that have been exposed to crude petroleum oil spills. Bacterial population of these polluted soils showed counts ranging between 9.5 x 10(5) and 237.5 x 10(5) CFU/g soil with 2 different colony types of bacterial strains which have been recovered on the agar plates. Results indicated that longer aged contamination exhibited a greater number of microorganisms. Phenotypic examination of the recovered bacteria revealed that they belong mainly to the genus Pseudomonas, Enterobacter and Acinetobacter. Turbidity, dry weight and physical appearance were used as an indication for the ability of these bacteria to grow on diesel. Action of three different Pseudomonas species, Acinetobacter lowffi, Enterobacter cloacae and Rhodococcus erythropolis on 0.1 % (v/v) diesel was followed at 1, 2, 6 and 12 h. Pseudomonas putida and P. mallei and Enterobacter cloacae indicated a positive reaction; however, Pseudomonas maltophilia and Acinetobacter lowffi showed no effect.

Bacteria↗
PubMed2002

Evaluation of carbazole degradation by Pseudomonas rhodesiae strain KK1 isolated from soil contaminated with coal tar.

In this study, strain KK1 isolated from coal tar-contaminated soil was found to be able to mineralize carbazole as a sole source of carbon by radiorespirometric analysis. KK1 cells pregrown on phenanthrene were able to mineralize carbazole much more rapidly than cells pregrown on naphthalene, suggesting a possible close linkage between the pathways for carbazole and phenanthrene catabolism. Also, Rieske-type iron sulfur center sequence of dioxygenase from KK1 was analyzed to evaluate carbazole catabolism by KK1. A gene cloned out from KK1 using a universal dioxygenase primer set was found a dioxygenase for initial catabolism of carbazole based on deduced amino acid sequences. Northern hybridization using the putative carbazole dixoygenase gene fragment as a probe provided the information that catabolism of carbazole might be greatly activated in phenanthrene-grown cells. Analysis of PLFAs extracted from KK1 cells exposed to carbazole revealed that lipids 10:0 3OH, 17:0 cyclo, and 18:0 were representatives produced or significantly increased in response to carbazole. Strain KK1 was identified as Pseudomonas species with 94% confidence when BIOLOG system was applied, as Pseudomonas sp. with over 90% confidence by total cellular compositions of fatty acid, and as Pseudomonas rhodesiae with 99% confidence by 16S rRNA sequence. Accordingly, strain KK1 was identified as Pseudomonas rhodesiae based on combination of the data, and designated Pseudomonas rhodesiae KK1. The phylogenetic tree based on 16S rRNA suggested that strain KK1 was far away in the phylogenetic distance from the strains that can degrade carbazole.

Amino Acid Sequence↗
PubMed2001

The effect of initial concentration of carbofuran on the development and stability of its enhanced biodegradation in top-soil and sub-soil.

Carbofuran was incubated in top-soil and sub-soil samples from a pesticide-free site at a range of initial concentrations from 0.1 to 10 mg kg-1. Amounts of the incubated soils were removed at intervals over the subsequent 12 months, and the rate of degradation of a second carbofuran dose at 10 mg kg-1 was assessed. An applied concentration as low as 0.1 mg kg-1 to top-soil resulted in more rapid degradation of the fresh addition of carbofuran for at least 12 months. The degree of enhancement was generally more pronounced with the higher initial concentrations. When the same study was conducted in sub-soil samples from the same site, an initial dose of carbofuran at 0.1 mg kg-1 resulted in only small increases in rates of degradation of a second carbofuran dose. However, degradation rates in the sub-soil samples were, in many instances, considerably greater than in the corresponding top-soil samples, irrespective of pre-treatment concentration or pre-incubated period. Initial doses of 0.5 mg kg-1 and higher applied to sub-soil successfully activated the sub-soil microflora. Application of the VARLEACH model to simulate carbofuran movement through the soil profile indicated that approximately 0.01 mg kg-1 of carbofuran may reach a depth of 70 cm 400 days after a standard field application. The results therefore imply that adaptation of the sub-soil microflora (c 1 m depth) by normal field rate applications of carbofuran is unlikely to occur. In experiments to investigate this in soils exposed to carbofuran in the field, there was no apparent relationship between top-soil exposure and degradation rates in the corresponding sub-soils. The results further confirmed that same sub-soil samples have an inherent capacity for rapid biodegradation of carbofuran. The high levels of variability observed between replicates in some of the sub-soil samples were attributed to the uneven distribution of a low population of carbofuran-degrading micro-organisms in sub-surface soil. There was no apparent relationship between soil microbial biomass and degradation rates within or between top-soil and sub-soil samples.

Bacteria↗
PubMed1993

Delayed and enhanced biodegradation of soil-applied diphenamid, carbendazim, and aldicarb.

Recent studies have demonstrated that interaction between various agrochemicals and soil microorganisms may either slow down or enhance processes of degradation. Soil disinfestation is employed for the control of soil-borne pathogens and weeds. Soil application of such broad-spectrum biocides, as well as some more selective chemicals, has a strong effect on microbial activity, which may result in drastic reduction in the rate of degradation of pesticides applied to such treated soils. Application of pesticides to previously disinfested soils may extend their biological activity, which in the case of herbicides could cause phytotoxic damage to the next crop. In contrast, repeated application of the same or structurally related pesticides may result in a selective buildup of microbial populations capable of degrading the pesticide at much faster rates. Cases of accelerated degradation were reported for pesticides belonging to various chemical groups. Studies were conducted to evaluate the mechanisms of accelerated degradation. For several pesticides it has been shown that soil fungi are involved in their normal degradation, but not in their accelerated degradation. The shift in the rate of degradation of pesticides such as diphenamid, benomyl, and S-ethyl dipropylthiocarbamate, in soils that have acquired accelerated degradation, seems to be associated with the buildup of populations of bacterial degraders. Moreover, it has been shown that for the herbicide diphenamide, accelerated degradation is apparently linked to the induction of an oxidative demethylation process in soil bacteria, which might be analogous to the development of resistance in pests. Contrary to studies demonstrating accelerated degradation of the systemic insecticide aldicarb and accumulation of aldicarb sulfoxide in non-history soils, our work has shown that repeated application of this carbamate at several locations in Israel over a 10-year period did not induce accelerated degradation. It should be pointed out that in the Israeli soils there was only minimal formation of aldicarb sulfoxide. These studies were performed in soils with a pH ranging from 7.8 to 8.3, which is higher than the pH reported for soils where accelerated degradation was detected.

Aldicarb↗
PubMed2002

Biodegradation of gasoline by gellan gum-encapsulated bacterial cells.

Encapsulated cell bioaugmentation is a novel alternative solution to in situ bioremediation of contaminated aquifers. This study was conducted to evaluate the feasibility of such a remediation strategy based on the performance of encapsulated cells in the biodegradation of gasoline, a major groundwater contaminant. An enriched bacterial consortium, isolated from a gasoline-polluted site, was encapsulated in gellan gum microbeads (16-53 microm diameter). The capacity of the encapsulated cells to degrade gasoline under aerobic conditions was evaluated in comparison with free (non-encapsulated) cells. Encapsulated cells (2.6 mg(cells) x g(-1) bead) degraded over 90% gasoline hydrocarbons (initial concentration 50-600 mg x L(-1)) within 5-10 days at 10 degrees C. Equivalent levels of free cells removed comparable amounts of gasoline (initial concentration 50-400 mg x L(-1)) within the same period but required up to 30 days to degrade the highest level of gasoline tested (600 mg x L(-1)). Free cells exhibited a lag phase in biodegradation, which increased from 1 to 5 days with an increase in gasoline concentration (200-600 x mg L(-1)). Encapsulation provided cells with a protective barrier against toxic hydrocarbons, eliminating the adaptation period required by free cells. The reduction of encapsulated cell mass loading from 2.6 to 1.0 mg(cells) x g(-1) bead caused a substantial decrease in the extent of biodegradation within a 30-day incubation period. Encapsulated cells dispersed within the porous soil matrix of saturated soil microcosms demonstrated a reduced performance in the removal of gasoline (initial concentrations of 400 and 600 mg x L(-1)), removing 30-50% gasoline hydrocarbons compared to 40-60% by free cells within 21 days of incubation. The results of this study suggest that gellan gum-encapsulated bacterial cells have the potential to be used for biodegradation of gasoline hydrocarbons in aqueous systems.

Bacteria↗
PubMed2002

Kinetic and inhibition studies for the aerobic cometabolism of 1,1,1-trichloroethane, 1,1-dichloroethylene, and 1,1-dichloroethane by a butane-grown mixed culture.

Batch kinetic and inhibition studies were performed for the aerobic cometabolism of 1,1,1-trichloroethane (1,1,1-TCA), 1,1-dichloroethylene (1,1-DCE), and 1,1-dichloroethane (1,1-DCA) by a butane-grown mixed culture. These chlorinated aliphatic hydrocarbons (CAHs) are often found together as cocontaminants in groundwater. The maximum degradation rates (k(max)) and half-saturation coefficients (K(s)) were determined in single compound kinetic tests. The highest k(max) was obtained for butane (2.6 micromol/mg TSS/h) followed by 1,1-DCE (1.3 micromol/mg TSS/h), 1,1-DCA (0.49 micromol/mg TSS/h), and 1,1,1-TCA (0.19 micromol/mg TSS/h), while the order of K(s) from the highest to lowest was 1,1-DCA (19 microM), butane (19 microM), 1,1,1-TCA (12 microM) and 1,1-DCE (1.5 microM). The inhibition types were determined using direct linear plots, while inhibition coefficients (K(ic) and K(iu)) were estimated by nonlinear least squares regression (NLSR) fits to the kinetic model of the identified inhibition type. Two different inhibition types were observed among the compounds. Competitive inhibition among CAHs was indicated from direct linear plots, and the CAHs also competitively inhibited butane utilization. 1,1-DCE was a stronger inhibitor than the other CAHs. Mixed inhibition of 1,1,1-TCA, 1,1-DCA, and 1,1-DCE transformations by butane was observed. Thus, both competitive and mixed inhibitions are important in cometabolism of CAHs by this butane culture. For competitive inhibition between CAHs, the ratio of the K(s) values was a reasonable indicator of competitive inhibition observed. Butane was a strong inhibitor of CAH transformation, having a much lower inhibition coefficient than the K(s) value of butane, while the CAHs were weak inhibitors of butane utilization. Model simulations of reactor systems where both the growth substrate and the CAHs are present indicate that reactor performance is significantly affected by inhibition type and inhibition coefficients. Thus, determining inhibition type and measuring inhibition coefficients is important in designing CAH treatment systems.

Bacteria, Aerobic↗
PubMed2003

The effects of metabolites from the indigenous Acidithiobacillus thiooxidans and temperature on the bioleaching of cadmium from soil.

The effect of metabolites from the indigenous Acidithiobacillus thiooxidans and temperature on the bioleaching of cadmium from soil was investigated in the present study. Bioleaching was found to be more effective than chemical leaching of cadmium. The metabolite, mainly sulfuric acid, which was shown to be growth-associated in the exponential phase, plays a major role in bioleaching. The maximum amount of cadmium leached was obtained after 8 days of precultivation when cells were directly involved in the leaching process. It indicates that cells in the exponential growth phase exhibit higher activity toward bioleaching. In contrast, the maximum amount of cadmium leached and the maximum initial rate for bioleaching were reached after 16 days of precultivation when only metabolites were involved in the bioleaching process. It implies that higher sulfuric acid concentration results in higher leaching efficiency. In addition, higher temperature leads to higher leaching efficiency. The optimal operation condition for bioleaching was determined to be a two-stage process: The first stage involves the precultivation of the indigenous A. thiooxidans at 30 degrees C for 8 days followed by 20 minutes of centrifugation to discard cells. The second stage involves the bioleaching with the subsequent supernatant at 50 degrees C.

Acidithiobacillus thiooxidans↗
PubMed2001

Electrokinetic movement and biodegradation of 2,4-dichlorophenoxyacetic acid in silt soil.

The coupling of electrokinetic movement of an organic contaminant, 2,4-dichlorophenoxyacetic acid (2,4-D), through soil and its biodegradation in situ has been demonstrated. In a first experiment, the direction and rate of movement of 2,4-D were determined using homogeneously contaminated soil (864 mg 2,4-D/kg dry weight soil) compacted into six individual compartments, 6 cm long, 3 cm wide, and 4 cm deep. Each compartment was bordered by a carbon felt anode and a stainless steel cathode. The application of a current density of 3.72 A/m(2) led to migration of 2,4-D towards the anode at a rate of approximately 4 cm/day. In a second experiment, electrokinetic movement and biodegradation were combined in situ. Sterilized silt soil contaminated with ring-labeled 14C-2,4-D (811 mg 2,4-D/kg dry weight soil) was compacted into a single soil compartment, 22 cm long, 7 cm wide, and 4 cm deep, in a 4.5 cm region adjacent to the cathode. The remainder of the compartment was filled with sterilized soil (to a total weight of 1,015 g). Burkholderia spp. RASC c2 (1.88 x 10(11) cells), a tetracycline-resistant bacterium with chromosomally encoded degradative genes for 2,4-D, was inoculated into the soil at a position 14-16 cm from the cathode. The reactor was placed within a sealed perspex box, with a constant air flow connected to sodium hydroxide traps. Under an applied current density of 0.89 A/m(2), the pollutant moved towards the bacteria. As it reached the inoculated region, its concentration decreased in the soil and 14CO2 was recovered in the traps. At the end of the experiment, 87.1% of radiolabel had been removed from the soil, 5.8% of which was recovered as 14CO2. A third, control, experiment showed a significant contrast in the absence of an electric current, where a slow rate of diffusion controlled the movement of both 2,4-D and bacteria in the soil and biodegradation occurred at the interface between the diffusing fronts.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2004

Effects of cyclodextrins, humic substances, and rhamnolipids on the washing of a historically contaminated soil and on the aerobic bioremediation of the resulting effluents.

Nontoxic and biodegradable pollutant-mobilizing agents, instead of chemical surfactants, were tested in the washing of an actual-site chloroaromatic-contaminated soil. A soil historically contaminated by chlorinated anilines and benzenes, thiophenes and several polycyclic aromatic hydrocarbons was subjected to washing by suspending it (15% w/v) in water or in water with 1.0% (w/v) beta-clodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), rhamnolipid (RL), dissolved humic substances (HS), or Triton X-100 (TX) in shaken batch reactors for 24 hr. The resulting wastewaters were amended with nutrients and treated aerobically in shaken reactors for 65 days. The biogenic agents markedly enhanced (by 237%, beta-CD; 265%, HP-beta-CD; 400%, RL; 566%, HS) the capability of water of eluting organic pollutants from the soil. TX enhanced the overall pollutant removal by about 660%; however, a lower depletion of the initial soil ecotoxicity, along with a more extensive impact on the soil organic matter, was observed. Furthermore, TX adversely affected the bioremediation of the resulting effluent by apparently inducing a premature decrease of specialized bacterial biomass. By contrast, the biogenic agents, and in particular HS and RL, sustained the biodegradation and dechlorination of pollutants by apparently enhancing the availability of specialized bacteria in the reactors. Thus, the biogenic agents proposed here seem to be promising nontoxic and nonaggressive soil washing agents for the integrated physicochemical (washing) and biological (aerobic posttreatment) restoration of poorly bioremediable (chloro) organics-contaminated soils.

Aerobiosis↗
PubMed2004

Effects of humic substances and soya lecithin on the aerobic bioremediation of a soil historically contaminated by polycyclic aromatic hydrocarbons (PAHs).

The high hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) strongly reduces their bioavailability in aged contaminated soils, thus limiting their bioremediation. The biodegradation of PAHs in soils can be enhanced by employing surface-active agents. However, chemical surfactants are often recalcitrant and exert toxic effects in the amended soils. The effects of two biogenic materials as pollutant-mobilizing agents on the aerobic bioremediation of an aged-contaminated soil were investigated here. A soil historically contaminated by about 13 g kg(-1) of a large variety of PAHs, was amended with soya lecithin (SL) or humic substances (HS) at 1.5% w/w and incubated in aerobic solid-phase and slurry-phase reactors for 150 days. A slow and only partial biodegradation of low-molecular weight PAHs, along with a moderate depletion of the initial soil ecotoxicity, was observed in the control reactors. The overall removal of PAHs in the presence of SL or HS was faster and more extensive and accompanied by a larger soil detoxification, especially under slurry-phase conditions. The SL and HS could be metabolized by soil aerobic microorganisms and enhanced the occurrence of both soil PAHs and indigenous aerobic PAH-degrading bacteria in the reactor water phase. These results indicate that SL and HS are biodegradable and efficiently enhance PAH bioavailability in soil. These natural surfactants significantly intensified the aerobic bioremediation of a historically PAH-contaminated soil under treatment conditions similar to those commonly employed in large-scale soil bioremediation.

Biodegradation, Environmental↗
PubMed2004

Stimulating in-soil rhamnolipid production in a bioslurry reactor by limiting nitrogen.

A soil with aged contamination from lubricating oil (LO) and polychlorinated biphenyls (PCBs) was treated in a bioslurry reactor to investigate in-soil biosurfactant production by Pseudomonas aeruginosa, the most abundant indigenous, culturable, hydrocarbon-degrading microorganism. After 2 days of growth on LO, a depletion of nitrogen stimulated the production and accumulation of rhamnolipids to levels roughly 20 times the critical micelle concentration. Surface tensions and concentrations of monorhamnolipid and dirhamnolipid, PCBs, and total petroleum hydrocarbons (TPH) were measured in a slurry filtrate. Soil-bound PCBs and TPH were also quantified. Rhamnolipid production was observed within 1 to 2 days after nitrogen depletion in each of the 10 batches tested. By day 6, total rhamnolipid concentrations increased from below detection to average values over 1,000 mg/L, which caused over 98% of soil-bound PCBs and over 99% of TPH to be emulsified and recovered in the filtrate. After 70 days, rhamnolipid concentrations were only reduced by 15%, because of nitrogen-limited rates of rhamnolipid biodegradation. The results show that in-soil biosurfactant production can be stimulated in a controlled way with nutrient limitation and can be used to achieve soil washing.

Bioreactors↗
PubMed2005

Degradation of aromatic hydrocarbons by white-rot fungi in a historically contaminated soil.

Phanerochaete chrysosporium NRRL 6361 and Pleurotus pulmonarius CBS 664.97 were tested for their ability to grow under nonsterile conditions and to degrade various aromatic hydrocarbons in an aged contaminated soil that also contained high concentrations of heavy metals. After 24 days fungal incubation, carbon-CO2 liberated, an indicator of microbial activity, reached a plateau. At the end of the incubation time (30 days), fungal colonization was clearly visible and was confirmed by ergosterol and cell organic carbon determinations. In spite of unfavorable pH (around 7.4) and the presence of heavy metals, both fungi produced Mn-peroxidase activity. In contrast, laccase and aryl-alcohol oxidase were detected only in the soil treated with P. pulmonarius CBS 664.97 and lignin-peroxidase in that with P. chrysosporium NRRL 6361. No lignin-modifying enzyme activities were present in non-inoculated soil incubated for 30 days (control microcosm). Regardless of the fungus employed, a total removal of naphtalene, tetrachlorobenzene, and dichloroaniline isomers, diphenylether and N-phenyl-1-naphtalenamine, was observed. Significant release of chloride ions was also observed in fungal-treated soil, in comparison with that recorded in the control microcosm. Both fungi led to a significant decrease in soil toxicity, as assessed using two different soil contact assays, including the Lepidium sativum L. germination test and the Collembola mortality test.

Biodegradation, Environmental↗
PubMed2006

Development and assessment of an innovative soil-washing process based on the use of cholic acid-derivatives as pollutant-mobilizing agents.

Surfactant-aided soil washing is often proposed for the restoration of aged organic pollutant-contaminated soils. As many of commercial surfactants have been found to be toxic and recalcitrant, the opportunity to use in this process cheap, non-toxic, and biodegradable pollutant-mobilizing agents, such as deoxycholic acid (DA), bovine bile (BB), and the residue resulting from DA extraction from BB (BBR), was studied in this work. A soil historically contaminated by chlorinated anilines and benzenes, thiophenes, and several polycyclic aromatic hydrocarbons was suspended at 15% w/v and washed in water or water amended at 1.0% (w/v) with DA, BB, BBR, or Triton X-100 (TX). The resulting effluents were supplemented with nutrients and subjected to aerobic bioremediation. The biogenic agents enhanced the water pollutant elution potential by 230/440%. TX enhanced the same parameter by about 540%; however, it mediated a lower depletion of the initial soil ecotoxicity and a more extensive mobilization of soil constituents with respect to the biogenic agents. Furthermore, TX adversely affected the biotreatability of resulting effluents, by adversely affecting the growth of cultivable bacterial biomass and the structure of eubacterial community of the effluent. On the contrary, the biogenic agents, and in particular DA and BB, enhanced the effluents bioremediation, by sustaining the growth and increasing the complexity of the effluent eubacterial communities. Thus, DA and BB are very promising additives for an effective and environmental friendly soil washing treatment of aged (chloro)organics contaminated soils.

Animals↗
PubMed2002

Stereoselective degradation of metalaxyl and metalaxyl-M in soil and sunflower plants.

A high proportion of agrochemicals are chiral compounds. Since stereoisomers often show different biological and physiological properties, the biological and metabolic responses to these compounds and their fate in the environment are expected to be different. In this work we investigate a possible stereo and/or enantioselective degradation in soil and plants (sunflower) of the fungicide Metalaxyl (rac-Metalaxyl) and the new compound Metalaxyl-M ((-)-(R)-Metalaxyl) and propose procedures for extraction, cleanup, chromatographic separation of enantiomers, and determination of the R : S ratio by using an HPLC chiral column. The degradation of the two stereoisomers of Metalaxyl proved to be enantioselective and dependent on the media: the (+)-(S)-enantiomer showed a faster degradation in plants, while the (-)-(R)-enantiomer showed a faster degradation in soil. In this study there was no evidence that racemization of Metalaxyl-M took place either in soil or in sunflowers.

Alanine↗
PubMed2003

Increased solubility of (heavy) metals in soil during microbial transformations of sucrose and casein amendments.

Unsterile soil samples pH 6.8 were amended with 10% sucrose or 0.1% NH4NO3/2% casein to influence solubility of metal cations. Microbial formation of aliphatic carboxylic acids reduced pH of sucrose soil to 4.3 and increased the solubility of heavy metals by 60-fold due to the increased presence of H+, and the metal-chelating and humic-molecule fragmenting properties of carboxylic acids. Soil pH increased finally to 7.8 upon the degradation of the carboxylic acids. In casein soil, ammonia production increased pH initially to 8.5 and promoted solubility of metal-containing humic compounds. Subsequent nitrification reduced pH to 5.6 to increase concentations of Ca and Mg in the soil solution, which prevented a comparable increase in the solubility of heavy metals competitively. It is concluded that amendment with sugar and nitrogen occasionally increases the concentrations of (hazardous) elements in the soil solution to facilitate their uptake by metal hyperaccumulating plants.

Bacteria↗
PubMed2005

Selection of bacteria and plant seeds for potential use in the remediation of diesel contaminated soils.

Enumeration and recovery of the dominant bacteria from a chronically fuel contaminated soil has been investigated. Bacterial counts from these polluted soils ranged between 0.70x10(8) and 28.20x10(8) CFU/g soil. Three different types of bacterial colonies have been recovered on the agar plates. Biochemical examination of the recovered bacteria revealed that they mainly belonged to the genus Pseudomonas, Micrococcus and Bacillus. Turbidity, cell biomass (dry weight basis), and physical appearance determined the growth of these bacteria on diesel. A noticeable decline in alfalfa (Medicago sativa) seeds germination of 15-30% was shown at 500 mg/kg diesel or higher. Under these contaminated conditions, fescue grass (Cyndon dactylon) exhibited a higher viability than alfalfa indicating that C. dactylon seeds are relatively tolerant to diesel and can possibly be used in phytoremediation of diesel contaminated soils. Results of diesel phyotoxicity to seed germination of these two plants were based on filter paper media and therefore; should be considered as first indication only. Extrapolation of such results to actual soil conditions should be cautiously approached taking into account diesel sorption on soil and mechanisms of its bioavailability.

Bacillus↗
PubMed2006

Bacterial community changes in diesel-oil-contaminated soil microcosms biostimulated with Luria-Bertani medium or bioaugmented with a petroleum-degrading bacterium, Pseudomonas aeruginosa strain WatG.

The microbial community structure of diesel-oil-contaminated soil microcosms biostimulated with Luria-Bertani medium (LB-BS) or bioaugmented with a petroleum-degrading bacterium, Pseudomonas aeruginosa strain WatG (WatG-BA), was investigated by denaturing gradient gel electrophoresis (DGGE) and by monitoring diesel oil degradation. The degradation in WatG-BA (64.0% +/- 4.2%) was higher than that in LB-BS (49.5% +/- 12.0%) during the first two weeks. The microbial community in WatG-BA, which was markedly dominated by strain WatG, was much simpler than that in LB-BS, where hydrocarbon degraders occurred after a lag of 3-7 days after the addition of diesel oil. The clustering profiles of the DGGE banding patterns of the two soil microcosms were only 12% similar. This difference is probably due to antibacterial substances, such as rhamnolipids, secreted by strain WatG.

Actinobacteria↗