Evaluation of microbial surfactants for recovery of hydrophobic pollutants from soil

Summary Several microbially produced biosurfactants were evaluated for their ability to remove hydrophobic compounds from soil. The biosurfactants produced byPseudomonas aeruginosa UG2 andAcinetobacter calcoaceticus RAG-1 displayed the best results, with recovery of [¹⁴C]hexachlorobiphenyl from soil slurries of 48.0 and 41.9%, respectively.P. aeruginosa UG2 produced higher levels of extracellular biosurfactants than four otherP. aeruginosa strains.P. aeruginosa UG2 culture filtrate containing biosurfactants enhanced the recovery of several other individual hydrocarbons and polychlorinated biphenyl compounds, as well as several hydrocarbons in a mixture, from soil. The results, suggest that biosurfactants produced byP. aeruginosa UG2 have the potential for remediation of hydrophobic pollutants in soil environments.     

Biosurfactants,an help in the biodegradation of hexadecane? The case of <Emphasis Type="Italic">Rhodococcus</Emphasis> and <Emphasis Type="Italic">Pseudomonas</Emphasis> strains

The roles of the extracellular biosurfactants produced by two bacterial strains, Pseudomonas aeruginosa GL1 and Rhodococcus equi Ou2, in hexadecane uptake and biodegradation were compared. For this purpose, cell hydrophobicity and production of glycolipidic biosurfactants were evaluated during bacterial growth on hexadecane, as well the effects of these biosurfactants on culture supernatants properties i.e., surface and interfacial tensions, and emulsification and pseudosolubilization capacities. The results showed that the role of biosurfactants was different in these two strains and was directly related to the hydrophobicity of the bacterial cells concerned. Extracellular biosurfactants produced by strain R. equi Ou2 had only a minor role in hexadecane degradation. Direct interfacial accession appeared to be the main mechanism for hexadecane uptake by the hydrophobic cells of strain R. equi Ou2. On the contrary, the biosurfactants produced by P. aeruginosa GL1 were required for growth on hexadecane, and their pseudosolubilization capacity rather than their emulsification capacity was involved in substrate degradation, allowing uptake from hexadecane micelles by the hydrophilic cells of this bacterium. The roles of biosurfactants thus differ widely among bacteria degrading hydrophobic compounds. J.-P. Vandecasteele—in retirement     

Comparison of lipopeptide biosurfactants production by Bacillus subtilis strains in submerged and solid state fermentation systems using a cheap carbon source: Some industrial applications of biosurfactants

Biosurfactants, in general has the potential to aid in the recovery of subsurface organic contaminants (environmental remediation) or crude oils (oil recovery). However, high production and purification costs limit its use in these high-volume applications. In the present study, the efficiency of two Bacillus subtilis strains viz., DM-03 and DM-04 for the production of biosurfactants in two fermentation systems viz., solid state fermentation (SSF) and submerged fermentation (SmF) was compared. Both the B. subtilis strains produced appreciable and equal amount of crude lipopeptide biosurfactants (B. subtilis DM-03: 80.0 ± 9 mg/gds in SmF and 67.0 ± 6 mg/gds in SSF; B. subtilis DM-04: 23.0 ± 5.0 mg/gds in SmF and 20.0 ± 2.5 mg/gds in SSF) in the two different fermentation systems using potato peels as cheap carbon source. These thermostable lipopeptide biosurfactants produced by B. subtilis strains either in SSF or in SmF, exhibited strong emulsifying property and could release appreciable amount of oil from saturated sand pack column. Further, it was shown by biochemical analysis, RP-HPLC profile and IR spectra that there is no qualitative and qualitative differences in the composition of crude biosurfactants produced either in SmF or in SSF system.     

Effect of surfactants on pyrene degradation by Pseudomonas fluorescens 29L

The effect of surfactants on pyrene degradation in Pseudomonas fluorescens 29L was investigated. This strain produced 30.1 μM of rhamnolipid equivalents (RE) of biosurfactants on 50 mg of pyrene per liter of medium. The production of biosurfactants was significantly correlated with the water solubility (S _w) of the substrate and the growth rate on it. When chrysene, with a S _w of 2.8 × 10⁻³ mg per liter of water, was the carbon source, 13.1 μM of RE of biosurfactants were produced compared to 10.3 μM of RE of biosurfactants on acenaphthene with a S _w of 1.9 mg per liter of water. No biosurfactants were produced on salicylic acid, catechol, and citrate. All of the strain 29L mutants which grew on pyrene produced biosurfactants while among the mutants which grew on naphthalene, only 88.4% produced biosurfactants. The rhamnolipid mixture, JBR425, inhibited the growth of Strain 29L wild type (WT) and all of its mutants on pyrene. However, these mutants were able to grow in the presence of pyrene when the growth medium was supplemented with 10⁻⁶ mg of emulsan per milliliter of medium. This study implies biosurfactants are produced by Strain 29L as a physiological response to the hydrophobicity of pyrene. The combined use of indigenous biosurfactants and the added biosurfactant, emulsan, is a biotechnology to enhance pyrene degradation by Pseudomonas fluorescens 29L.     

Cultivar response against root-infecting fungi and efficacy of Pseudomonas aeruginosa in controlling soybean root rot

Abstract

A study was conducted in the greenhouse to examine the resistance of three soybean cultivars against root-infecting fungi, and to determine the role of five strains of Pseudomonas aeruginosa in protecting the roots from these fungal pathogens. In this study soybean cv RAWAL was found to be less susceptible against charcoal rot fungus Macrophomina phaseolina than cvs PARC and BRAGG. Most of the strains of P. aeruginosa used as seed dressing significantly reduced M. phaseolina and Rhizoctonia solani infection on all three cvs PARC, BRAGG and RAWAL (p < 0.05). Most of the strains of P. aeruginosa were effective on cv PARC against Fusarium solani infection, while on cv BRAGG P. aeruginosa strain Pa₃, and on cv RAWAL strain Pa₅ were effective. Both strains Pa₃ and Pa₂₂ gave maximum plant height and fresh weight of shoots, respectively on cvs PARC and BRAGG than other strains. These characteristics make these P. aeruginosa strains good candidates for use as biocontrol agents against soil-borne plant pathogens.     

A Biosurfactant-Producing Pseudomonas aeruginosa Strain

A Pseudomonas aeruginosa strain producing an extracellular surfactant (biosurfactant) was isolated. The growth of this strain, referred to as 50.3, on a mineral glycerol-containing medium produces an emulsifying activity (60%) and decreases the surface tension of the culture liquid by a factor of 2.8 (to 25 mN/m). The optimum conditions for its growth and production of biosurfactants are intense aeration, pH 7.0–8.0, and the presence of Mg²⁺. The optimum biosurfactant properties were achieved when glucose was used as the only source of carbon and energy and NH₄Cl was used as a source of nitrogen. The biosurfactant was isolated from the culture liquid by extraction and precipitation.     

Functional response of Anodonta anatina feeding on a green alga and four strains of cyanobacteria, differing in shape, size and toxicity

We studied the functional response of the freshwater unionid bivalve Anodonta anatina, feeding on five phytoplankton strains differing in food quality: the small green alga Scenedesmus obliquus, a toxic and a non-toxic strain of the filamentous cyanobacterium Planktothrix agardhii and a toxic and a non-toxic strain of the coccoid cyanobacterium Microcystis aeruginosa. On S. obliquus, A. anatina had a type II functional response with a maximum mass-specific ingestion rate (IR_max) of 5.24 mg C g DW⁻¹ h⁻¹ and a maximum mass-specific clearance rate (CR_max) of 492 (±38) ml g DW⁻¹ h⁻¹, the highest values for all the phytoplankton strains that were investigated. On toxic and non-toxic P. agardhii filaments, A. anatina also had a type II functional response, but IR_max and CR_max were considerably lower (IR_max 1.90 and 1.56 mg C g DW⁻¹ h⁻¹; CR_max 387 (±97) and 429 (±71) ml g DW⁻¹ h⁻¹, respectively) than on S. obliquus. Toxicity of P. agardhii had no effect on the filtration rate of the mussels. On the non-toxic M. aeruginosa (small coccoid cells), we also observed a type II functional response, although a type I functional response fitted almost as good to these data. For the colonial and toxic M. aeruginosa, a type I functional response fitted best to the data: IR increased linearly with food concentration and CR remained constant. CR_max and IR_max values for the (colonial) toxic M. aeruginosa (383 (±40) ml g DW⁻¹ h⁻¹; 3.7 mg C g DW⁻¹ h⁻¹) demonstrated that A. anatina filtered and ingested this cyanobacterium as good as the other cyanobacterial strains. However, on the non-toxic M. aeruginosa we observed the lowest CR_max of all phytoplankters (246 (±23) ml g DW⁻¹ h⁻¹, whereas IR_max was similar to that on toxic M. aeruginosa. The high maximum ingestion rates on S. obliquus and M. aeruginosa indicate a short handling time of these phytoplankton species. The high clearance rates on S. obliquus, toxic M. aeruginosa and P. agardhii reflect a high effort of the mussels to filter these particles out of the water column at low concentrations. The low clearance rates on non-toxic M. aeruginosa may be explained by the small size and coccoid form of this cyanobacterium, which may have impaired A. anatina to efficiently capture the cells. Although A. anatina had relatively high maximum clearance rates on non-toxic and toxic P. agardhii, this cyanobacterium does not seem to be a good food source, because of the observed high rates of pseudofaeces production and hence low ingestion rates.     

Rhamnolipid biosurfactants: evolutionary implications,applications and future prospects from untapped marine resource

Rhamnolipid-biosurfactants are known to be produced by the genus Pseudomonas, however recent literature reported that rhamnolipids (RLs) are distributed among diverse microbial genera. To integrate the evolutionary implications of rhamnosyl transferase among various groups of microorganisms, a comprehensive comparative motif analysis was performed amongst bacterial producers. Findings on new RL-producing microorganism is helpful from a biotechnological perspective and to replace infective P. aeruginosa strains which ultimately ensure industrially safe production of RLs. Halotolerant biosurfactants are required for efficient bioremediation of marine oil spills. An insight on the exploitation of marine microbes as the potential source of RL biosurfactants is highlighted in the present review. An economic production process, solid-state fermentation using agro-industrial and industrial waste would increase the scope of biosurfactants commercialization. Potential and prospective applications of RL-biosurfactants including hydrocarbon bioremediation, heavy metal removal, antibiofilm activity/biofilm disruption and greener synthesis of nanoparticles are highlighted in this review.     

Antimicrobial and antioxidant activities of methanol extracts of <Emphasis Type="Italic">Evax pygmaea</Emphasis> (Asteraceae) growing wild in Tunisia

Antimicrobial activity of methanolic extracts obtained from the aerial parts of Evax pygmaea was tested against five bacteria and two strains of phytopathogenic fungi using the agar diffusion and broth microdilution methods. Antioxidant properties were evaluated through the ability of the different fractions to scavenge the stable ABTS (2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals. The TEAC (Trolox Equivalent Antioxidant Capacity) and IC₅₀ values of the fractions were calculated and compared. The experimental data indicated that all fractions exhibit moderate to appreciable antibacterial activities against all Gram-positive cocci and Gram-negative rods except Pseudomonas aeruginosa, but no antifungal activity was observed. Ethyl acetate and methanol fractions were found to cause significant free radical-scavenging effects in both assays. These results may suggest that E. pygmaea could be used as a natural preservative ingredient in the food and/or pharmaceutical industries.     

Pseudomonas aeruginosa PAO1 as a model for rhamnolipid production in bioreactor systems

Rhamnolipids are biosurfactants with interesting physico-chemical properties. However, the main obstacles towards an economic production are low productivity, high raw-material costs, relatively expensive downstream processing, and a lack of understanding the rhamnolipid production regulation in bioreactor systems. This study shows that the sequenced Pseudomonas aeruginosa strain PAO1 is able to produce high quantities of rhamnolipid during 30 L batch bioreactor cultivations with sunflower oil as sole carbon source and nitrogen limiting conditions. Thus PAO1 could be an appropriate model for rhamnolipid production in pilot plant bioreactor systems. In contrast to well-established production strains, PAO1 allows knowledge-based systems biotechnological process development combined with the frequently used heuristic bioengineering approach. The maximum rhamnolipid concentration obtained was 39 g/L after 90 h of cultivation. The volumetric productivity of 0.43 g/Lh was comparable with previous described production strains. The specific rhamnolipid productivity showed a maximum between 40 and 70 h of process time of 0.088 g_RL/g_BDMh. At the same time interval, a shift of the molar di- to mono-rhamnolipid ratio from 1:1 to about 2:1 was observed. PAO1 not only seems to be an appropriate model, but surprisingly has the potential as a strain of choice for actual biotechnological rhamnolipid production.     

Rhamnolipid production by a novel thermophilic hydrocarbon-degrading Pseudomonas aeruginosa AP02-1

Thermophilic bacterial cultures were isolated from a hot spring environment on hydrocarbon containing mineral salts media. One strain identified as Pseudomonas aeruginosa AP02-1 was tested for the ability to utilize a range of hydrocarbons both n-alkanes and polycyclic aromatic hydrocarbons as sole carbon source. Strain AP02-1 had an optimum growth temperature of 45°C and degraded 99% of crude oil 1% (v/v) and diesel oil 2% (v/v) when added to a basal mineral medium within 7 days of incubation. Surface activity measurements indicated that biosurfactants, mainly glycolipid in nature, were produced during the microbial growth on hydrocarbons as well as on both water-soluble and insoluble substrates. Mass spectrometry analysis showed different types of rhamnolipid production depending on the carbon substrate and culture conditions. Grown on glycerol, P. aeruginosa AP02-1 produced a mixture of ten rhamnolipid homologues, of which Rha-Rha-C₁₀-C₁₀ and Rha-C₁₀-C₁₀ were predominant. Rhamnolipid-containing culture broths reduced the surface tension to ≈28 mN and gave stable emulsions with a number of hydrocarbons and remained effective after sterilization. Microscopic observations of the emulsions suggested that hydrophobic cells acted as emulsion-stabilizing agents.     

Production and characterization of a group of bioemulsifiers from the marine Bacillus velezensis strain H3

Marine microbes are a rich source of bioactive compounds, such as drugs, enzymes, and biosurfactants. To explore the bioactive compounds from our marine natural product library, an oil emulsification assay was applied to discover biosurfactants and bioemulsifiers. A spore-forming bacterial strain from sea mud was found to produce bioemulsifiers with good biosurfactant activity and a broad spectrum of antimicrobial properties. It was identified as Bacillus velezensis H3 using genomic and phenotypic data analysis. This strain was able to produce biosurfactants with an optimum emulsification activity at pH 6.0 and 2% NaCl by using starch as the carbon source and ammonium sulfate as the nitrogen source. The emulsification-guided isolation and purification procedure led to the discovery of the biosurfactant components, which were mainly composed of nC₁₄-surfactin and anteisoC₁₅-surfactin as determined by NMR and MS spectra. These compounds can reduce the surface tension of phosphate-buffered saline (PBS) from 71.8 to 24.8 mN/m. The critical micelle concentrations (CMCs) of C₁₄-surfactin and C₁₅-surfactin in 0.1 M PBS (pH 8.0) were determined to be 3.06?×?10^-5 and 2.03?×?10^-5?mol/L, respectively. The surface tension values at CMCs for C₁₄-surfactin and C₁₅-surfactin were 25.7 and 27.0 mM/m, respectively. In addition, the H3 biosurfactant exhibited antimicrobial activities against Staphyloccocus aureus, Mycobacterium, Klebsiella peneumoniae, Pseudomonas aeruginosa, and Candida albicans. Thus B. velezensis H3 is an alternative surfactin producer with potential application as an industrial strain for the lipopeptide production.     

Variation of Microcystin Content of Cyanobacterial Blooms and Isolated Strains in Lake Grand-Lieu (France)

Abstract Cyanobacterial blooms were sampled at five locations in Lake Grand-Lieu on seven different occasions during May–October 1994. Strains of Microcystis aeruginosa and Anabaena circinalis were isolated from the samples. Microcystins were detected in freeze-dried field samples and the isolated strains by HPLC. The toxins were present in the blooms sampled between June and October. The microcystin content in the blooms varied with site and time, from undetectable concentrations to 0.23 mg g⁻¹. The highest concentrations of microcystin were found in blooms sampled in September. Microcystin-LR and microcystins with retention times close to the retention time of [Dha⁷]microcystin-RR (probably varieties of microcystin-RR) were found in the field samples. Sixteen of the 98 isolated M. aeruginosa strains and 2 of the 24 A. circinalis strains produced microcystins. The total amount of microcystins varied from undetectable concentrations to 5.06 mg g⁻¹ in the M. aeruginosa isolates, and from undetectable concentrations to 1.86 mg g⁻¹ in the A. circinalis strains. Microcystin-LR was the main toxin found in strains of M. aeruginosa, but was not present in strains of A. circinalis. Both microcystin-producing strains and strains that did not produce microcystin coexisted in the bloom samples. Received: 23 January 1997; Accepted: 25 March 1997     

Biosurfactant-Mediated Biodegradation of Polycyclic Aromatic Hydrocarbons—Naphthalene

The present study is aimed at the naphthalene degradation with and without biosurfactant produced from Pseudomonas aeruginosa isolated from oil-contaminated soil. The present study was carried out to isolate the bacterial strains for the naphthalene degradation and also for biosurfactant production. The isolated strains were screened for their ability to degrade the naphthalene by the methods of optimum growth rate test and for the production of biosurfactants by cetyltrimethylammonium bromide, blood agar medium, and thin-layer chromatography. The present study also focused on the effect of biosurfactant for the degradation of naphthalene by isolate-1. Two bacterial strains were isolated and screened, one for biodegradation and another for biosurfactant production. The second organism was identified as Pseudomonas aeruginosa by 16S rRNA analysis. The purified biosurfactant reduces the surface tension of water and also forms stable emulsification with hexadecane and kerosene. The end product of naphthalene degradation was estimated as salicylic acid equivalent by spectrophotometric method. The results demonstrated that Pseudomonas aeruginosa has the potential to produce biosurfactant, which enhances the biodegradation of naphthalene. The study reflects the potential use of biosurfactants for an effective bioremediation in the management of contaminated soils.     

Isolation and Characterization of Phenol-catabolizing Bacteria from a Coking Plant

New phenol degrading bacteria with high biodegradation activity and high tolerance were isolated as Burkholderia cepacia PW3 and Pseudomonas aeruginosa AT2. Both isolates could grow aerobically on phenol as a sole carbon source even at 3 g/l. The whole-cell kinetic properties for phenol degradation by strains PW3 and AT2 showed a V_max of 0.321 and 0.253 mg/l/min/(mg protein), respectively. The metabolic pathways for phenol biodegradation in both strains were assigned to the meta-cleavage activity of catechol 2,3-dioxygenase.     

Toxic and non-toxic strains of Microcystis aeruginosa induce temperature dependent allelopathy toward growth and photosynthesis of Chlorella vulgaris

Global warming was believed to accelerate the expansion of cyanobacterial blooms. However, the impact of changes due to the allelopathic effects of cyanobacterial blooms with or without algal toxin production on the ecophysiology of its coexisting phytoplankton species arising from global warming were unknown until recently. In this study, the allelopathic effects of toxic and non-toxic Microcystis aeruginosa strains on the growth of green alga Chlorella vulgaris and photosynthesis of the co-cultivations of C. vulgaris and toxic M. aeruginosa FACHB-905 or non-toxic M. aeruginosa FACHB-469 were investigated at different temperatures. The growth of C. vulgaris, co-cultured with the toxic or non-toxic M. aeruginosa strains, was promoted at 20 °C but inhibited at temperatures ≥25 °C. The inhibitory effects of the toxic and non-toxic M. aeruginosa strains on of the co-cultivations (C. vulgaris and non-toxic M. aeruginosa FACHB-469 or toxic M. aeruginosa FACHB-905) also linearly increased with elevated temperatures. Furthermore, toxic M. aeruginosa FACHB-905 induced more inhibition toward growth of C. vulgaris or P_max and R_d of the mixtures than non-toxic M. aeruginosa FACHB-469. C. vulgaris dominated over non-toxic M. aeruginosa FACHB-469 but toxic M. aeruginosa FACHB-905 overcame C. vulgaris when they were co-cultured in mesocosms in water temperatures from 20 to 25 °C. The results indicate that allelopathic effects of M. aeruginosa strains on C. vulgaris are both temperature- and species-dependent: it was stimulative for C. vulgaris at low temperatures such as 20 °C, but inhibitory at high temperatures (≥25 °C); the toxic strain was determined to be more harmful to C. vulgaris than the non-toxic one. This suggests that global warming may aggravate the ecological risk of cyanobacteria blooms, especially those with toxic species as the main contributors.     

Ammonia may play an important role in the succession of cyanobacterial blooms and the distribution of common algal species in shallow freshwater lakes

With the human intensification of agricultural and industrial activities, large amount of reduced nitrogen enter into the biosphere, which consequently results in the development of global eutrophication and cyanobacterial blooms. However, no research had reported the effect of ammonia toxicity on the algal succession. In this study, we investigated the ammonia toxicity to 19 algal species or strains to test the hypothesis that ammonia may regulate the succession of cyanobacterial blooms and the distribution of common algal species in freshwater lakes. The bloom‐forming cyanobacterium Microcystis aeruginosa PCC 7806 suffered from ammonia toxicity at high pH value and light intensity conditions. Low NH₄Cl concentration (0.06 mmol L^?1) resulted in the decrease of operational PSII quantum yield by 50% compared with the control exposed to 1000 μmol photons m^?2 s^?1 for 1 h at pH 9.0 ± 0.2, which can be reached in freshwater lakes. Furthermore, the tolerant abilities to NH₃ toxicity of 18 freshwater algal species or strains were as follows: hypertrophication species > eutrophication species > mesotrophication species > oligotrophication species. The different sensitivities of NH₃ toxicity in this study could well explain the distributing rule of common algal species in the freshwater lakes of different trophic states. Meanwhile, the cyanobacterial bloom (e.g. M. aeruginosa) always happened at the low concentration of ammonia in summer, and disappeared with the decrease of ammonia. This may be attributed to the toxic effect of ammonia to M. aeruginosa in spring (the average and maximum ammonia concentration were 0.08 and 0.72 mmol L^?1 in 33 Chinese lakes), and the low level of NH₃‐N in summer and fall in the lakes might be used as preferred nitrogen nutrition by M. aeruginosa, rather than with toxicity. Therefore, ammonia could be a key factor to determine the distribution of common algal species and cyanobacterial bloom in the freshwater systems.     

Physiological aspects of hydrocarbon emulsification, metal resistance and DNA profile of biodegrading bacteria isolated from oil polluted sites

The production of biosurfactants was evaluated for seven bacterial strains isolated from different oil contaminated sites by the Emulsification Index using diesel oil as the hydrocarbon source. Minimum Inhibitory Concentrations of Mg²⁺, Cr³⁺ and Cu²⁺ were determined to identify the less sensitive bacteria in order to select the best strains for bioremediation. Plasmid extraction was also performed in order to search for gene sequences involved with biosurfactant synthesis. All strains were able to emulsify diesel oil. Rhodococcus ruber AC239 presented the best index (58%), followed by other Rhodococcus strains. Pseudomonas aeruginosa, R. ruber AC239, AC87 and R. erytropolis AC272 presented smallest sensitivities to heavy metals used, being suitable for use in sites contaminated with high concentrations of them. No plasmid DNA was detected showing that biosurfactant coding genes should be in the chromosomal DNA.     

Effect of drought stress on growth and water relations of the mycorrhizal association Helianthemum almeriense-Terfezia claveryi

 Plants of Helianthemum almeriense were micropropagated on MS medium and inoculated in vitro with Terfezia claveryi mycelium on MH medium and vermiculite. Mycorrhizal (M) and non-mycorrhizal (NM) plants were subjected to a drought stress period of 3 weeks in greenhouse conditions with the soil matric potential maintained at –0.5 MPa. Drought stress did not affect the amount of mycorrhizal colonization. The survival rate of M plants at the end of the drought stress period was higher than that of NM plants. The water potential was higher in M plants than in NM plants by 14% in well-watered and 26% in drought-stressed plants. Transpiration, stomatal conductance and net photosynthesis were higher in M plants than in NM plants. Transpiration was 92% higher in M plants than in NM plants under drought-stress conditions and 40% when irrigated. Stomatal conductance was 45% and 14% higher and net photosynthesis 88% and 54% higher, respectively, in M than in NM plants. Drought-stressed M plants accumulated more N, P and K than drought-stressed NM plants. Reduced negative effects of drought stress on H. almeriense by the desert truffle T. claveryi could be ascribed to specific physiological and nutritional mechanisms, suggesting that this mycorrhizal symbiosis aids adaptation to arid climates. Accepted: 7 July 2000     

Biosurfactant production by two isolates ofPseudomonas aeruginosa

Two strains of biosurfactant-producing bacteria, identified asPseudomonas aeruginosa, were isolated from injection water and crude oil-associated water in Venezuelan oil fields. Both biosurfactants resembled rhamnolipids and produced stable emulsions of heavy and extra-heavy crude oils, reducing the surface tension of water from 72 to 28 dynes/cm. Tenso-active properties of the biosurfactants were not affected by pH, temperature, salinity or Ca²⁺ or Mg²⁺ at concentrations in excess of those found in many oil reservoirs in Venezuela.