Comparison of autochthonous bacteria and commercially available cultures with respect to their effectiveness in fuel oil degradation

Influence of pollution history on the response of coastal bacterial and nanoeukaryote communities to crude oil and biostimulation assays

Pollution history has often been proposed to explain site-dependent bioremediation efficiencies, but this hypothesis has been poorly explored. Here, bacteria and their heterotrophic nanoflagellates (HNF) predators originating from pristine and chronically oil-polluted coastal sites were subjected to crude oil ± nutrients or emulsifier amendments. The addition of crude oil had a more visible effect on bacteria originating from the pristine site with a higher increase in the activity of given OTU and inactivation of other petroleum-sensitive bacteria, as revealed by DNA and RNA-based comparison. Such changes resulted in a delay in microbial growth and in a lower bacterial degradation of the more complex hydrocarbons. Biostimulation provoked a selection of different bacterial community assemblages and stirred metabolically active bacteria. This resulted in a clear increase of the peak of bacteria and their HNF predators and higher oil degradation, irrespective of the pollution history of the site.

Multi-factors on biodegradation kinetics of polycyclic aromatic hydrocarbons (PAHs) by Sphingomonas sp. a bacterial strain isolated from mangrove sediment

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediment is an attractive remediation technique and its success depends on biodegradation kinetics, and the optimal condition for the PAH-degrading isolates; however, information on this aspect is still scarce. The effects of multi-factors on biodegradation of phenanthrene, a 3-ring model PAH, in contaminated sediment slurry by Sphingomonas sp. a bacterial strain isolated from surface mangrove sediment, were investigated using the orthogonal experimental design (form L(16)(4(5))). The most significant factors were salinity and inoculum size, while the effects of phenanthrene concentrations, nutrient addition and temperatures were insignificant. The optimal biodegradation condition in contaminated mangrove sediment slurry was 30 degrees C, 15 ppt salinity, a carbon/nitrogen ratio of 100:1 (the background ratio in sediment) and an inoculum size of 10(6) most probable number g(-1) sediment. The phenanthrene biodegradation could be best described by the first order rate model, C=C(0)e(-kt), where k (the rate constant) is equaled to 0.1185, under the optimal condition. The kinetic model was verified and its validity in predicting biodegradation by Sphingomonas sp. at various phenanthrene concentrations was proved by experimental data.

Protocol for laboratory testing of crude-oil bioremediation products in freshwater conditions

In 1993, the Environmental Protection Agency, National Risk Management Research Laboratory (EPA, NRMRL), with the National Environmental Technology Application Center (NETAC), developed a protocol for evaluation of bioremediation products in marine environments [18]. The marine protocol was adapted for application in freshwater environments by using a chemically defined medium and an oil-degrading consortium as a positive control. Four products were tested using the modified protocol: two with nutrients and an oleophilic component; one with nutrients, sorbent, and organisms; and one microbial stimulant. A separate experiment evaluated the use of HEPES and MOPSO buffers as replacements for phosphate buffer. The oleophilic nutrient products yielded oil degradation similar to the positive control, with an average alkane removal of 97.1+/-2.3% and an aromatic hydrocarbon removal of 64.8+/-1.2%. The positive control, which received inoculum plus nutrients, demonstrated alkane degradation of 98.9+/-0.1% and aromatic degradation of 52.9+/-0.1%. The sorbent-based product with inoculum failed to demonstrate oil degradation, while the microbial stimulant showed less oil degradation than the positive control. Replacement of phosphate buffer with other buffers had no significant effect on one product's performance. Differences in product performance were easily distinguishable using the protocol, and performance targets for alkane and aromatic hydrocarbon degradation are suggested.

The fate of diesel hydrocarbons in soils and their effect on the germination of perennial ryegrass

Hydrocarbon contamination in soils may be toxic to plants and soil microorganisms and act as a source of groundwater contamination. The objective of this study was to evaluate the fate of diesel in soils with or without added nutrients. The soils examined either had or had not a previous history of hydrocarbon contamination. Particular aspects examined were soil respiration, changes in microbial population, breakdown of diesel hydrocarbons, and phytotoxicity to the germination of perennial ryegrass. Soil respiration was measured as evolved CO2. Bacterial population was determined as colony forming units in dilution plates and fungal activity was measured as hyphal length. The fate of individual hydrocarbons was determined by gas chromatography-mass spectrometry after extraction with dichloromethane. When diesel was added to soil with no previous history of hydrocarbon contamination at rates up to 50 mg/g, the respiration response showed a lag phase of 6 days and maximum respiration occurred at day 11. The lag phase was 2 days and maximum respiration occurred at day 3 in soil with a previous history of hydrocarbon contamination. After the peak, respiration decreased up to about 20 days in both soils. Thereafter, respiration become more or less constant but substantially greater than the control. N and P addition along with diesel did not reduce the lag phase but increased the respiration over the first 20 days of incubation. Diesel addition with or without N and P increased the bacterial population 10- to 100-fold but fungal hyphal length did not increase. Diesel addition at a rate of 136 mg/g did not increase the microbial population. Removal of inhibition to germination of perennial ryegrass was linked to the decomposition of nC10 and nC11 hydrocarbons and took from 11 to 30 days at diesel additions up to 50 mg/g depending on the soil. Inhibition to germination of perennial ryegrass persisted to more than 24 weeks at the 136 mg/g of diesel addition.

Biodegradation of phenanthrene in soil

We investigated the potential of an aerobic polycyclic aromatic hydrocarbon (PAH)-adapted consortium to degrade phenanthrene in soil. Optimal degradation conditions were determined as pH7.0 and 30 degrees C with a water content of 100% wt soil/wt water (w/w). At a concentration of 5 microg/g, phenanthrene degradation (k1) was measured at 0.0269 l/hr with a half-life (t(1/2)) of 25.8 hrs. Our results show that the higher the phenanthrene concentration, the slower the degradation rates. Phenanthrene degradation was enhanced by treatment with yeast extract, glucose, or pyruvate, but was not significantly improved by the addition of acetate. Degradation was delayed by the addition of either compost or potassium nitrate and enhanced by the addition of nonionic surfactants (Brij30, Brij35, Triton X100 or Triton N101) at critical micelle concentration (CMC). Phenanthrene degradation was delayed at levels above CMC.

Bioremediation of petroleum hydrocarbon-contaminated soil by composting in biopiles

Composting of contaminated soil in biopiles is an ex situ technology, where organic matter such as bark chips are added to contaminated soil as a bulking agent. Composting of lubricating oil-contaminated soil was performed in field scale ( [Formula: see text] m(3)) using bark chips as the bulking agent, and two commercially available mixed microbial inocula as well as the effect of the level of added nutrients (N,P,K) were tested. Composting of diesel oil-contaminated soil was also performed at one level of nutrient addition and with no inoculum. The mineral oil degradation rate was most rapid during the first months, and it followed a typical first order degradation curve. During 5 months, composting of the mineral oil decreased in all piles with lubrication oil from approximately 2400 to 700 mg (kg dry w)(-1), which was about 70% of the mineral oil content. Correspondingly, the mineral oil content in the pile with diesel oil-contaminated soil decreased with 71% from 700 to 200 mg (kg dry w)(-1). In this type of treatment with addition of a large amount of organic matter, the general microbial activity as measured by soil respiration was enhanced and no particular effect of added inocula was observed.

Biomarkers for monitoring efficacy of bioremediation by microbial inoculants

Bioaugmentation of contaminated sites with microbes that are adapted or genetically engineered for degradation of specific toxic compounds is an area that is currently being explored as a clean-up option. Biomarkers have been developed to track the survival and efficacy of specific bacteria that are used as inocula for bioremediation of contaminated soil. Examples of biomarkers include the luc gene, encoding firefly luciferase and the gfp gene, encoding the green fluorescent protein (GFP). The luc gene was used to tag different bacteria used for bioremediation of gasoline or chlorophenols. The bacteria were monitored on the basis of luciferase activity in cell extracts from soil. The gfp gene was also used to monitor bacteria during degradation of chlorophenol in soil, based on fluorescence of the GFP protein. Other biomarkers can also be used for monitoring of microbial inocula used for bioaugmentation of contaminated sites. The choice of biomarker and monitoring system depends on the particular site, bacterial strain and sensitivity and specificity of detection required.

Laboratory evaluation of crude oil biodegradation with commercial or natural microbial inocula

Experiments have been performed to screen eight microbial commercial products that, according to the manufacturers, are able to degrade crude oil. This study compared the crude oil biodegradation activity of commercial inocula with that of natural inocula (activated sludge and tropical aquarium water). Some of the latter were previously adapted to the crude oil as the only carbon source. Nutrients and sorbents in the commercial formulations were eliminated, and each inoculum was precultured on marine yeast extract medium. Crude oil biodegradability tests were conducted with close initial substrate concentration to initial bacterial concentration ratios (S0/X0) of 0.94 g of crude oil/109CFU, which allowed a comparison of biodegradation activity. The inocula oxidized the crude oil after a short lag time of less than 3-18 days. After that time, the rate of oxidation varied between 45 and 244 mg O2/(L·day). Crude oil biodegradation after a 28-day test was effective only for 10 out of 12 inocula (from 0.1 to 25% in weight). Biodegradation mainly corresponded to the saturated fraction of the crude oil; the asphaltene fraction was never significantly biodegraded. Our results led to the conclusion that natural inocula, either adapted or not adapted to crude oil, were the most active (from 16 to 25% of loss in crude oil weight) and only one commercial inoculum was able to degrade 18% of the crude oil. Other inocula had a biodegradation activity ranging from 0.1 to 14%.Key words: biodegradability tests, microbial inoculum, crude oil, seeding.

Effect of drying on bioremediation bacteria properties

Bioremediation bacteria with drought-resistance characteristics were selected and compared to a collection of 10 strains selected only for their bioremediation properties. Twenty-six strains were selected from dried diesel-polluted soil, and they exhibit a better level of survival during drying, compared to collection bioremediation strains (two orders of magnitude difference). The lyophilization process does not affect the strains' ability to grow on xenobiotic compound when measured immediately after drying. However, collection bioremediation strains selected only for their bioremediation properties lose up to 80% of their properties when stored at 25 degrees C for 15 d, but the strains selected for their drought resistance lose their properties to a lesser extent during the same period. The maximal growth rate and the rate of xenobiotic degradation of the still-active cells are not affected by the drying process.

Impact of inoculation protocols, salinity, and pH on the degradation of polycyclic aromatic hydrocarbons (PAHs) and survival of PAH-degrading bacteria introduced into soil

Degradation of polycyclic aromatic hydrocarbons (PAHs) and survival of bacteria in soil was investigated by applying different inoculation protocols. The soil was inoculated with Sphingomonas paucimobilis BA 2 and strain BP 9, which are able to degrade anthracene and pyrene, respectively. CFU of soil bacteria and of the introduced bacteria were monitored in native and sterilized soil at different pHs. Introduction with mineral medium inhibited PAH degradation by the autochthonous microflora and by the strains tested. After introduction with water (without increase of the pore water salinity), no inhibition of the autochthonous microflora was observed and both strains exhibited PAH degradation.

Petroleum spill bioremediation in marine environments

Bioremediation is a promising technology for responding to marine oil spills. A majority of molecules in crude oils and refined products are biodegradable, and they will eventually leave the environment as they are consumed by microbes. Bioremediation aims to stimulate the rate of this process. Successful bioremediation efforts have so far focused on applying fertilizers to aerobic oiled shorelines to at least partially relieve the nitrogen limitation of biodegradation by indigenous microorganisms. Nevertheless, there seems to be room for improving the process by developing better fertilizers, developing surfactants to stimulate degradation, and perhaps using exogenous bacteria. There also is room to extend the application to oiled marshes and other anaerobic sediments, and perhaps to floating slicks. This review covers our present understanding of hydrocarbon degradation in the marine environment, and discusses field trials and field use of bioremediation as an important adjunct to other tools for responding to marine oil spills.