Enhanced biodegradation of diesel oil by a newly identified Rhodococcus baikonurensis EN3 in the presence of mycolic acid

PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70-95% for fluorene, 44-89% for phenanthrene, 86-97% for anthracene, and 6.5-78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198's ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.

Continuous bioreactors enable high-level bioremediation of diesel-contaminated seawater at low and mesophilic temperatures using Antarctic bacterial consortia: Pollutant analysis and microbial community composition

In 2020, more than 21,000 tons of diesel oil were released accidently into the environment with most of it contaminating water bodies. There is an urgent need for sustainable technologies to clean up rivers and oceans to protect wildlife and human health. One solution is harnessing the power of bacterial consortia; however isolated microbes from different environments have shown low diesel bioremediation rates in seawater thus far. An outstanding question is whether Antarctic microorganisms that thrive in environments polluted with hydrocarbons exhibit better diesel degrading activities when propagated at higher temperatures than those encountered in their natural ecosystems. Here, we isolated bacterial consortia, LR-30 (30 °C) and LR-10 (10 °C), from the Antarctic rhizosphere soil of Deschampsia antarctica (Livingston Island), that used diesel oil as the only carbon substrate. We found that LR-30 and LR-10 batch bioreactors metabolized nearly the entire diesel content when the initial concentration was 10 (g/L) in seawater. Increasing the initial diesel concentration to 50 gDiesel/L, LR-30 and LR-10 bioconverted 33.4 and 31.2 gDiesel/L in 7 days, respectively. The 16S rRNA gene sequencing profiles revealed that the dominant bacterial genera of the inoculated LR-30 community were Achromobacter (50.6%), Pseudomonas (25%) and Rhodanobacter (14.9%), whereas for LR-10 were Pseudomonas (58%), Candidimonas (10.3%) and Renibacterium (7.8%). We also established continuous bioreactors for diesel biodegradation where LR-30 bioremediated diesel at an unprecedent rate of (34.4 g/L per day), while LR-10 achieved (24.5 g/L per day) at 10 °C for one month. The abundance of each bacterial genera present significantly fluctuated at some point during the diesel bioremediation process, yet Achromobacter and Pseudomonas were the most abundant member at the end of the batch and continuous bioreactors for LR-30 and LR-10, respectively.

Impact of diesel and biodiesel contamination on soil microbial community activity and structure

Soil contamination as a result of oil spills is a serious issue due to the global demand for diesel fuel. As an alternative to diesel, biodiesel has been introduced based on its high degradability rates and potential for reducing of greenhouse gases emissions. This study assessed the impacts diesel and biodiesel contamination on soil microbial community activity and structure. Our results suggest higher microbial activity in biodiesel contaminated soils and analysis of PLFA profiles confirmed shifts in microbial community structure in response to contamination. High-throughput 16S rRNA amplicon sequencing also revealed a lower bacterial richness and diversity in contaminated soils when compared to control samples, supporting evidence of the detrimental effects of hydrocarbons on soil microbiota. Control samples comprised mostly of Actinobacteria, whereas Proteobacteria were predominantly observed in diesel and biodiesel contaminated soils. At genus level, diesel and biodiesel amendments highly selected for Rhodococcus and Pseudomonas spp., respectively. Moreover, predicted functional profiles based on hydrocarbon-degrading enzymes revealed significant differences between contaminated soils mostly due to the chemical composition of diesel and biodiesel fuel. Here, we also identified that Burkholderiaceae, Novosphingobium, Anaeromyxobacter, Pseudomonas and Rhodococcus were the main bacterial taxa contributing to these enzymes. Together, this study supports the evidence of diesel/biodiesel adverse effects in soil microbial community structure and highlights microbial taxa that could be further investigated for their biodegradation potential.

Mesocosm-based simulations to optimize a bioremediation strategy for the effective restoration of wildfire-impacted soils contaminated with high-molecular-weight hydrocarbons

AIMS

We obtained four microbial isolates from soil exposed to forest fire and evaluated their potential bioremediation activity when combined with a biosurfactant-producing bacterial strain for the decontamination of wildfire-impacted soil polluted with high-molecular-weight (HMW) hydrocarbons.

METHODS AND RESULTS

We established mesocosm trials to compare three bioremediation strategies: natural attenuation, bioaugmentation and biostimulation. Chemical analysis, culture-dependent and culture-independent methods were used to evaluate the bioremediation efficiency and speciation of the microbial cenoses based on these approaches. After treatment for 90 days, bioaugmentation removed 75·2-75·9% of the HMW hydrocarbons, biostimulation removed 63·2-69·5% and natural attenuation removed ~22·5%. Hydrocarbon degradation was significantly enhanced in the mesocosm supplemented with the biosurfactant-producing bacterial strain after 20 and 50 days of treatment compared to the other bioremediation strategies.

CONCLUSIONS

We found that the bioaugmentation approach was more effective than biostimulation and natural attenuation for the removal of HMW hydrocarbons from fire-impacted soil.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study showed that micro-organisms from wildfire-impacted soil show significant potential for bioremediation, and that biosurfactant-producing bacterial strains can be combined with them as part of an effective bioremediation strategy.

Tween 20 regulate the function and structure of transmembrane proteins of Bacillus cereus: Promoting transmembrane transport of fluoranthene

Polycyclic aromatic hydrocarbons (PAHs) are degraded by the highly efficient degrading bacterium Bacillus cereus. Transmembrane transport is highly important in PAH degradation by bacteria. Surfactants are the key substances that promote PAH adsorption, uptake and transmembrane transport by Bacillus cereus. In this study, the isobaric tags for relative and absolute quantitation (iTRAQ) approach was used for high-throughput screening of key functional proteins during transmembrane fluoranthene transport by Bacillus cereus treated with Tween 20. In addition, SWISS-MODEL was used to simulate the tertiary structures of key transmembrane proteins and analyze how Tween 20 promotes transmembrane transport. Transmembrane fluoranthene transport into Bacillus cereus requires transmembrane proteins and energy. Tween 20 was observed to improve bacterial motility and transmembrane protein expression. The interior of representative transmembrane proteins is mostly composed of hydrophobic β-sheets while amphipathic α-helices are primarily distributed at their periphery. The primary reason for this configuration may be α-helices promote the aggregation of surfactants and the phospholipid bilayer and the β-sheets promote surfactant insertion into the phospholipid bilayer to enhance PAH transport into Bacillus cereus. Investigating the effect of Tween 20 on Bacillus cereus transmembrane proteins during transmembrane fluoranthene transport is important for understanding the mechanism of PAH degradation by microorganisms.

Isolation, identification, and characterization of diesel-oil-degrading bacterial strains indigenous to Changqing oil field, China

In the present study, 12 indigenous diesel-oil-degrading bacteria were isolated from the petroleum-contaminated soils of the Changqing oil field (Xi'an, China). Measurement of the diesel-oil degradation rates of these strains by the gravimetric method revealed that they ranged from 42% to 66% within 2 weeks. The highest degradation rates were observed from strains CQ8-1 (66%), CQ8-2 (62.6%), and CQ11 (59%), which were identified as Bacillus thuringiensis, Ochrobactrum anthropi, and Bordetella bronchialis, respectively, based on their 16S rDNA sequences. Moreover, the physiological and biochemical properties of these three strains were analyzed by Gram staining, catalase, oxidase, and Voges-Proskauer tests. Transmission electron microscopy showed that all three strains were rod shaped with flagella. Gas chromatography and mass spectrometric analyses indicated that medium- and long-chain n-alkanes in diesel oil (C11-C29) were degraded to different degrees by B. thuringiensis, O. anthropi, and B. bronchialis, and the degradation rates gradually decreased as the carbon numbers increased. Overall, the results of this study indicate strains CQ8-1, CQ8-2, and CQ11 might be useful for environmentally friendly and cost-effective bioremediation of oil-contaminated soils.

Microbial communities associated with barley growing in an oil sands reclamation area in Alberta, Canada

Microbial communities that colonize the plant rhizosphere and the root interior can ameliorate plant stress and promote growth. These plant–microbe associations are being investigated to assist in reclamation soils in northern Alberta. This study assessed the diversity of bacterial species associated with barley plants growing at different cover managements and slope positions in an oil sands reclamation area. Phospholipid fatty acid analysis of the microbial communities indicated that both cover type and slope, in addition to soil total and organic carbon, NH4+, and organic matter, were significant determinants of microbial community composition. However, analysis of denaturing gel gradient electrophoresis (DGGE) banding patterns revealed that while most bulk and rhizosphere soils differentiated by cover management, no clustering was observed in endophytes. In addition, techniques to assess culture-dependent endophytic bacteria revealed a dominance of the class Gammaproteobacteria, in which Enterobacteriaceae (44%), Xanthomonaceae (30%), and Pseudomonaceae (26%) were the most abundant families in this class. Several endophytic isolates also matched those from DGGE profiles. The results of this study suggest that plants growing on oil sands reclamation covers host a wide range of bacterial endophytes, which should be assessed as to their potential to assist plant establishment and growth at such sites.

Simulating the fate of indigenous antibiotic resistant bacteria in a mild slope wastewater polluted stream

The fate of indigenous surface-water and wastewater antibiotic resistant bacteria in a mild slope stream simulated through a hydraulic channel was investigated in outdoor experiments. The effect of (i) natural (dark) decay, (ii) sunlight, (iii) cloudy cover, (iv) adsorption to the sediment, (v) hydraulic conditions, (vi) discharge of urban wastewater treatment plant (UWTP) effluent and (vii) bacterial species (presumptive Escherichia coli and enterococci) was evaluated. Half-life time (T_1/2) of E. coli under sunlight was in the range 6.48-27.7min (initial bacterial concentration of 10⁵CFU/mL) depending on hydraulic and sunlight conditions. E. coli inactivation was quite similar in sunny and cloudy day experiments in the early 2hr, despite of the light intensity gradient was in the range of 15-59W/m²; but subsequently the inactivation rate decreased in the cloudy day experiment (T_1/2=23.0min) compared to sunny day (T_1/2=17.4min). The adsorption of bacterial cells to the sediment (biofilm) increased in the first hour and then was quite stable for the remaining experimental time. Finally, when the discharge of an UWTP effluent in the stream was simulated, the proportion of indigenous antibiotic resistant E. coli and enterococci was found to increase as the exposure time increased, thus showing a higher resistance to solar inactivation compared to the respective total populations.

From oil spills to barley growth - oil-degrading soil bacteria and their promoting effects

Heavy contamination of soils by crude oil is omnipresent in areas of oil recovery and exploitation. Bioremediation by indigenous plants in cooperation with hydrocarbon degrading microorganisms is an economically and ecologically feasible means to reclaim contaminated soils. To study the effects of indigenous soil bacteria capable of utilizing oil hydrocarbons on biomass production of plants growing in oil-contaminated soils eight bacterial strains were isolated from contaminated soils in Kazakhstan and characterized for their abilities to degrade oil components. Four of them, identified as species of Gordonia and Rhodococcus turned out to be effective degraders. They produced a variety of organic acids from oil components, of which 59 were identified and 7 of them are hitherto unknown acidic oil metabolites. One of them, Rhodococcus erythropolis SBUG 2054, utilized more than 140 oil components. Inoculating barley seeds together with different combinations of these bacterial strains restored normal growth of the plants on contaminated soils, demonstrating the power of this approach for bioremediation. Furthermore, we suggest that the plant promoting effect of these bacteria is not only due to the elimination of toxic oil hydrocarbons but possibly also to the accumulation of a variety of organic acids which modulate the barley's rhizosphere environment.

Pseudosolubilized n-alkanes analysis and optimization of biosurfactants production by Pseudomonas sp. DG17

The pseudosolubilized medium-chain-length n-alkanes during biodegradation process, and optimization of medium composition and culture conditions for rhamnolipid production by Pseudomonas sp. DG17 using Plackett-Burman design and Box-Behnken design, were examined in this study. The results showed that pseudosolubilized concentration of C14 to C20 n-alkanes was higher than that of C24 to C26. After incubation for 120 h, pseudosolubilized C16H34 increased to 2.63 ± 0.21 mg. Meanwhile, biodegradation rates of n-alkanes decreased along with the increase of carbon chain length. Carbon-14 assay suggested that nonlabeled C14H30, C16H34, and C20H42 inhibited the biodegradation of (14)C n-octadecane, and Pseudomonas sp. DG17 utilized different alkanes simultaneously. Three significant variables (substrate concentration, salinity, and C/N) that could influence rhamnolipid production were screened by Plackett-Burman design. Results of Box-Behnken design suggested that rhamnolipid concentration could be achieved at 91.24 mg L(-1) (observed value) or 87.92 mg L(-1) (predicted value) with the optimal levels of concentration, salinity, and C/N of 400 mg L(-1), 1.5 %, and 45, respectively.

The detection and phylogenetic analysis of the alkane 1-monooxygenase gene of members of the genus Rhodococcus

Naturally occurring and anthropogenic petroleum hydrocarbons are potential carbon sources for many bacteria. The AlkB-related alkane hydroxylases, which are integral membrane non-heme iron enzymes, play a key role in the microbial degradation of many of these hydrocarbons. Several members of the genus Rhodococcus are well-known alkane degraders and are known to harbor multiple alkB genes encoding for different alkane 1-monooxygenases. In the present study, 48 Rhodococcus strains, representing 35 species of the genus, were investigated to find out whether there was a dominant type of alkB gene widespread among species of the genus that could be used as a phylogenetic marker. Phylogenetic analysis of rhodococcal alkB gene sequences indicated that a certain type of alkB gene was present in almost every member of the genus Rhodococcus. These alkB genes were common in a unique nucleotide sequence stretch absent from other types of rhodococcal alkB genes that encoded a conserved amino acid motif: WLG(I/V/L)D(G/D)GL. The sequence identity of the targeted alkB gene in Rhodococcus ranged from 78.5 to 99.2% and showed higher nucleotide sequence variation at the inter-species level compared to the 16S rRNA gene (93.9-99.8%). The results indicated that the alkB gene type investigated might be applicable for: (i) differentiating closely related Rhodococcus species, (ii) properly assigning environmental isolates to existing Rhodococcus species, and finally (iii) assessing whether a new Rhodococcus isolate represents a novel species of the genus.

Alkane-degrading properties of Dietzia sp. H0B, a key player in the Prestige oil spill biodegradation (NW Spain)

AIMS

Investigation of the alkane-degrading properties of Dietzia sp. H0B, one of the isolated Corynebacterineae strains that became dominant after the Prestige oil spill.

METHODS AND RESULTS

Using molecular and chemical analyses, the alkane-degrading properties of strain Dietzia sp. H0B were analysed. This Grampositive isolate was able to grow on n-alkanes ranging from C₁₂ to C₃₈ and branched alkanes (pristane and phytane). 8-Hexadecene was detected as an intermediate of hexadecane degradation by Dietzia H0B, suggesting a novel alkane-degrading pathway in this strain. Three putative alkane hydroxylase genes (one alkB homologue and two CYP153 gene homologues of cytochrome P450 family) were PCR-amplified from Dietzia H0B and differed from previously known hydroxylase genes, which might be related to the novel degrading activity observed on Dietzia H0B. The alkane degradation activity and the alkB and CYP153 gene expression were observed constitutively regardless of the presence of the substrate, suggesting additional, novel pathways for alkane degradation.

CONCLUSIONS

The results from this study suggest novel alkane-degrading pathways in Dietzia H0B and a genetic background coding for two different putative oil-degrading enzymes, which is mostly unexplored and worth to be subject of further functional analysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study increases the scarce information available about the genetic background of alkane degradation in genus Dietzia and suggests new pathways and novel expression mechanisms of alkane degradation.

Characterization of two diesel fuel degrading microbial consortia enriched from a non acclimated, complex source of microorganisms

BACKGROUND

The bioremediation of soils impacted by diesel fuels is very often limited by the lack of indigenous microflora with the required broad substrate specificity. In such cases, the soil inoculation with cultures with the desired catabolic capabilities (bioaugmentation) is an essential option. The use of consortia of microorganisms obtained from rich sources of microbes (e.g., sludges, composts, manure) via enrichment (i.e., serial growth transfers) on the polluting hydrocarbons would provide bioremediation enhancements more robust and reproducible than those achieved with specialized pure cultures or tailored combinations (co-cultures) of them, together with none or minor risks of soil loading with unrelated or pathogenic allocthonous microorganisms.

RESULTS

In this work, two microbial consortia, i.e., ENZ-G1 and ENZ-G2, were enriched from ENZYVEBA (a complex commercial source of microorganisms) on Diesel (G1) and HiQ Diesel (G2), respectively, and characterized in terms of microbial composition and hydrocarbon biodegradation capability and specificity. ENZ-G1 and ENZ-G2 exhibited a comparable and remarkable biodegradation capability and specificity towards n-C10 to n-C24 linear paraffins by removing about 90% of 1 g l-1 of diesel fuel applied after 10 days of aerobic shaken flask batch culture incubation at 30 degrees C. Cultivation dependent and independent approaches evidenced that both consortia consist of bacteria belonging to the genera Chryseobacterium, Acinetobacter, Psudomonas, Stenotrophomonas, Alcaligenes and Gordonia along with the fungus Trametes gibbosa. However, only the fungus was found to grow and remarkably biodegrade G1 and G2 hydrocarbons under the same conditions. The biodegradation activity and specificity and the microbial composition of ENZ-G1 and ENZ-G2 did not significantly change after cryopreservation and storage at -20 degrees C for several months.

CONCLUSIONS

ENZ-G1 and ENZ-G2 are very similar highly enriched consortia of bacteria and a fungus capable of extensively degrading a broad range of the hydrocarbons mainly composing diesel fuels. Given their remarkable biodegradation potential, stability and resistance to cryopreservation, both consortia appear very interesting candidates for bioaugmentation operations on Diesel fuel impacted soils and sites.

Bacterial communities from shoreline environments (costa da morte, northwestern Spain) affected by the prestige oil spill

The bacterial communities in two different shoreline matrices, rocks and sand, from the Costa da Morte, northwestern Spain, were investigated 12 months after being affected by the Prestige oil spill. Culture-based and culture-independent approaches were used to compare the bacterial diversity present in these environments with that at a nonoiled site. A long-term effect of fuel on the microbial communities in the oiled sand and rock was suggested by the higher proportion of alkane and polyaromatic hydrocarbon (PAH) degraders and the differences in denaturing gradient gel electrophoresis patterns compared with those of the reference site. Members of the classes Alphaproteobacteria and Actinobacteria were the prevailing groups of bacteria detected in both matrices, although the sand bacterial community exhibited higher species richness than the rock bacterial community did. Culture-dependent and -independent approaches suggested that the genus Rhodococcus could play a key role in the in situ degradation of the alkane fraction of the Prestige fuel together with other members of the suborder Corynebacterineae. Moreover, other members of this suborder, such as Mycobacterium spp., together with Sphingomonadaceae bacteria (mainly Lutibacterium anuloederans), were related as well to the degradation of the aromatic fraction of the Prestige fuel. The multiapproach methodology applied in the present study allowed us to assess the complexity of autochthonous microbial communities related to the degradation of heavy fuel from the Prestige and to isolate some of their components for a further physiological study. Since several Corynebacterineae members related to the degradation of alkanes and PAHs were frequently detected in this and other supralittoral environments affected by the Prestige oil spill along the northwestern Spanish coast, the addition of mycolic acids to bioremediation amendments is proposed to favor the presence of these degraders in long-term fuel pollution-affected areas with similar characteristics.

Assessment of microbial diversity in effluent treatment plants by culture dependent and culture independent approaches

Microbial community structure of two distinct effluent treatment plants (ETPs) of pesticide and pharmaceutical industries was assessed and defined by (i) culture dependent and culture independent approaches on the basis of 16S rRNA gene sequencing, (ii) diversity index analysis - operational taxonomic units (OTUs). A total of 38 and 44 bacterial OTUs having 85-99% similarity with the closest match in the database were detected among pharmaceutical and pesticide sludge samples, respectively. Fifty percent of the OTUs were related to uncultured bacteria. These OTUs had a Shannon diversity index value of 2.09-2.33 for culturables and in the range of 3.25-3.38 for unculturables. The high species evenness values of 0.86 and 0.95 indicated the vastness of microbial diversity retrieved by these approaches. The dominant cultured bacteria indicative of microbial diversity in functional ETPs were Alcaligenes, Bacillus and Pseudomonas. Brevundimonas, Citrobacter, Pandoraea and Stenotrophomonas were specific to pesticide ETP and Agrobacterium, Brevibacterium, Micrococcus, Microbacterium, Paracoccus and Rhodococcus were specific to pharmaceutical ETP. These microbes can thus be maintained and exploited for efficient functioning and maintenance of ETPs.

Variability of enzyme system of Nocardioform bacteria as a basis of their metabolic activity

The present review describes some aspects of organization of biodegradative pathways of Nocardioform microorganisms, first of all, with respect to their ability to degrade aromatic compounds, mostly methylbenzoate, chlorosubstituted phenols, and chlorinated biphenyls and the intermediates of their transformation: 4-chlorobenzoate and para-hydroxybenzoate. Various enzyme systems induced during degradation processes are defined. The ability of microorganisms to induce a few key enzymes under the influence of xenobiotics is described. This ability may increase the biodegradative potential of strains allowing them to survive in the changing environment or demonstrate to some extent the unspecific response of microorganisms to the effect of toxicants. Nocardioform microorganisms responsible for degradation of such persistent compounds as polychlorinated biphenyls, polyaromatic hydrocarbons, chlorinated benzoates and phenols and other xenobiotics are characterized. The possibility of using Nocardioform microorganisms in some aspects of biotechnology due to their ability to produce some compounds important for industry is also estimated.

Biodegradability of commercial and weathered diesel oils

This work aimed to evaluate the capability of different microorganisms to degrade commercial diesel oil in comparison to a weathered diesel oil collected from the groundwater at a petrol station. Two microbiological methods were used for the biodegradability assessment: the technique based on the redox indicator 2,6 -dichlorophenol indophenol (DCPIP) and soil respirometric experiments using biometer flasks. In the former we tested the bacterial cultures Staphylococcus hominis, Kocuria palustris, Pseudomonas aeruginosa LBI, Ochrobactrum anthropi and Bacillus cereus, a commercial inoculum, consortia obtained from soil and groundwater contaminated with hydrocarbons and a consortium from an uncontaminated area. In the respirometric experiments it was evaluated the capability of the native microorganisms present in the soil from a petrol station to biodegrade the diesel oils. The redox indicator experiments showed that only the consortia, even that from an uncontaminated area, were able to biodegrade the weathered diesel. In 48 days, the removal of the total petroleum hydrocarbons (TPH) in the respirometric experiments was approximately 2.5 times greater when the commercial diesel oil was used. This difference was caused by the consumption of labile hydrocarbons, present in greater quantities in the commercial diesel oil, as demonstrated by gas chromatographic analyses. Thus, results indicate that biodegradability studies that do not consider the weathering effect of the pollutants may over estimate biodegradation rates and when the bioaugmentation is necessary, the best strategy would be that one based on injection of consortia, because even cultures with recognised capability of biodegrading hydrocarbons may fail when applied isolated.

Bacterial metabolism of long-chain n-alkanes

Degradation of alkanes is a widespread phenomenon in nature, and numerous microorganisms, both prokaryotic and eukaryotic, capable of utilizing these substrates as a carbon and energy source have been isolated and characterized. In this review, we summarize recent advances in the understanding of bacterial metabolism of long-chain n-alkanes. Bacterial strategies for accessing these highly hydrophobic substrates are presented, along with systems for their enzymatic degradation and conversion into products of potential industrial value. We further summarize the current knowledge on the regulation of bacterial long-chain n-alkane metabolism and survey progress in understanding bacterial pathways for utilization of n-alkanes under anaerobic conditions.

Hydrocarbon emulsification and enhanced crude oil degradation by lauroyl glucose ester

Enzymatically synthesized lauroyl glucose emulsified different hydrophobic substrates when assayed spectrophotometrically. Stable emulsions were formed with triglycerides as well as with hydrocarbons. There was a linear relation between the concentration of lauroyl glucose (50-450 microg) and emulsification activity under the assay conditions when tested with aromatic and aliphatic hydrocarbons. This sugar ester was able to emulsify the aromatic hydrocarbons benzene, toluene and xylene. Long chain alkanes (n-decane and n-hexadecane) as well as brominated long chain alkanes (1-bromodecane and 1-bromohexadecane) were efficiently emulsified. The effect of lauroyl glucose ester on degradation of crude oil by a known oil-degrading Rhodococcus species was also investigated. The culture showed enhanced degradation of crude oil when lauroyl glucose ester was used as an emulsifier. It degraded 70% of the aliphatic fraction of Bombay High crude oil in the presence of the sugar ester at a concentration of 200mg l(-1) as compared to 50% without the emulsifier.