High-performance liquid chromatography method for the characterization of rhamnolipid mixtures produced by pseudomonas aeruginosa UG2 on corn oil

Dry powder inhalation containing muco-inert ciprofloxacin and colistin co-loaded liposomes for pulmonary P. Aeruginosa biofilm eradication

Pseudomonas aeruginosa (PA), a predominant pathogen in lung infections, poses significant challenges due to its biofilm formation, which is the primary cause of chronic and recalcitrant pulmonary infections. Bacteria within these biofilms exhibit heightened resistance to antibiotics compared to their planktonic counterparts, and their secreted toxins exacerbate lung infections. Diverging from traditional antibacterial therapy for biofilm eradication, this study introduces a novel dry powder inhalation containing muco-inert ciprofloxacin and colistin co-encapsulated liposomes (Cipro-Col-Lips) prepared using ultrasonic spray freeze drying (USFD) technique. This USFD dry powder is designed to efficiently deliver muco-inert Cipro-Col-Lips to the lungs. Once deposited, the liposomes rapidly diffuse into the airway mucus, reaching the biofilm sites. The muco-inert Cipro-Col-Lips neutralize the biofilm-secreted toxins and simultaneously trigger the release of their therapeutic payload, exerting a synergistic antibiofilm effect. Our results demonstrated that the optimal USFD liposomal dry powder formulation exhibited satisfactory in vitro aerosol performance in terms of fine particle fraction (FPF) of 44.44 ± 0.78 %, mass median aerodynamic diameter (MMAD) of 4.27 ± 0.21 μm, and emitted dose (ED) of 99.31 ± 3.31 %. The muco-inert Cipro-Col-Lips effectively penetrate the airway mucus and accumulate at the biofilm site, neutralizing toxins and safeguarding lung cells. The triggered release of ciprofloxacin and colistin works synergistically to reduce the biofilm's antibiotic resistance, impede the development of antibiotic resistance, and eliminate 99.99 % of biofilm-embedded bacteria, including persister bacteria. Using a PA-beads induced biofilm-associated lung infection mouse model, the in vivo efficacy of this liposomal dry powder aerosol was tested, and the results demonstrated that this liposomal dry powder aerosol achieved a 99.7 % reduction in bacterial colonization, and significantly mitigated inflammation and pulmonary fibrosis. The USFD dry powder inhalation containing muco-inert Cipro-Col-Lips emerges as a promising therapeutic strategy for treating PA biofilm-associated lung infections.

Microbe cultivation guidelines to optimize rhamnolipid applications

In the growing landscape of interest in natural surfactants, selecting the appropriate one for specific applications remains challenging. The extensive, yet often unsystematized, knowledge of microbial surfactants, predominantly represented by rhamnolipids (RLs), typically does not translate beyond the conditions presented in scientific publications. This limitation stems from the numerous variables and their interdependencies that characterize microbial surfactant production. We hypothesized that a computational recipe for biosynthesizing RLs with targeted applicational properties could be developed from existing literature and experimental data. We amassed literature data on RL biosynthesis and micellar solubilization and augmented it with our experimental results on the solubilization of triglycerides (TGs), a topic underrepresented in current literature. Utilizing this data, we constructed mathematical models that can predict RL characteristics and solubilization efficiency, represented as logPRL = f(carbon and nitrogen source, parameters of biosynthesis) and logMSR = f(solubilizate, rhamnolipid (e.g. logPRL), parameters of solubilization), respectively. The models, characterized by robust R2 values of respectively 0.581-0.997 and 0.804, enabled the ranking of descriptors based on their significance and impact-positive or negative-on the predicted values. These models have been translated into ready-to-use calculators, tools designed to streamline the selection process for identifying a biosurfactant optimally suited for intended applications.

Swarming of P. aeruginosa: Through the lens of biophysics

Swarming is a collective flagella-dependent movement of bacteria across a surface that is observed across many species of bacteria. Due to the prevalence and diversity of this motility modality, multiple models of swarming have been proposed, but a consensus on a general mechanism for swarming is still lacking. Here, we focus on swarming by Pseudomonas aeruginosa due to the abundance of experimental data and multiple models for this species, including interpretations that are rooted in biology and biophysics. In this review, we address three outstanding questions about P. aeruginosa swarming: what drives the outward expansion of a swarm, what causes the formation of dendritic patterns (tendrils), and what are the roles of flagella? We review models that propose biologically active mechanisms including surfactant sensing as well as fluid mechanics-based models that consider swarms as thin liquid films. Finally, we reconcile recent observations of P. aeruginosa swarms with early definitions of swarming. This analysis suggests that mechanisms associated with sliding motility have a critical role in P. aeruginosa swarm formation.

The Glycine-Glucolipid of Alcanivorax borkumensis Is Resident to the Bacterial Cell Wall

The marine bacterium Alcanivorax borkumensis produces a surface-active glycine-glucolipid during growth with long-chain alkanes. A high-performance liquid chromatography (HPLC) method was developed for absolute quantification. This method is based on the conversion of the glycine-glucolipid to phenacyl esters with subsequent measurement by HPLC with diode array detection (HPLC-DAD). Different molecular species were separated by HPLC and identified as glucosyl-tetra(3-hydroxy-acyl)-glycine with varying numbers of 3-hydroxy-decanoic acid or 3-hydroxy-octanoic acid groups via mass spectrometry. The growth rate of A. borkumensis cells with pyruvate as the sole carbon source was elevated compared to hexadecane as recorded by the increase in cell density as well as oxygen/carbon dioxide transfer rates. The amount of the glycine-glucolipid produced per cell during growth on hexadecane was higher compared with growth on pyruvate. The glycine-glucolipid from pyruvate-grown cells contained considerable amounts of 3-hydroxy-octanoic acid, in contrast to hexadecane-grown cells, which almost exclusively incorporated 3-hydroxy-decanoic acid into the glycine-glucolipid. The predominant proportion of the glycine-glucolipid was found in the cell pellet, while only minute amounts were present in the cell-free supernatant. The glycine-glucolipid isolated from the bacterial cell broth, cell pellet, or cell-free supernatant showed the same structure containing a glycine residue, in contrast to previous reports, which suggested that a glycine-free form of the glucolipid exists which is secreted into the supernatant. In conclusion, the glycine-glucolipid of A. borkumensis is resident to the cell wall and enables the bacterium to bind and solubilize alkanes at the lipid-water interface. IMPORTANCE Alcanivorax borkumensis is one of the most abundant marine bacteria found in areas of oil spills, where it degrades alkanes. The production of a glycine-glucolipid is considered an essential element for alkane degradation. We developed a quantitative method and determined the structure of the A. borkumensis glycine-glucolipid in different fractions of the cultures after growth in various media. Our results show that the amount of the glycine-glucolipid in the cells by far exceeds the amount measured in the supernatant, confirming the proposed cell wall localization. These results support the scenario that the surface hydrophobicity of A. borkumensis cells increases by producing the glycine-glucolipid, allowing the cells to attach to the alkane-water interface and form a biofilm. We found no evidence for a glycine-free form of the glucolipid.

Guava Seed Oil: Potential Waste for the Rhamnolipids Production

Guava is consumed in natura and is also of considerable importance to the food industry. The seeds and peel of this fruit are discarded, however, guava seeds yield oil (~13%) that can be used for the bioproducts synthesis. The use of a by-product as a carbon source is advantageous, as it reduces the environmental impact of possible harmful materials to nature, while adding value to products. In addition, the use of untested substrates can bring new yield and characterization results. Thus, this research sought to study rhamnolipids (RLs) production from guava seed oil, a by-product of the fructorefinery. The experiments were carried out using Pseudomonas aeruginosa LBI 2A1 and experimental design was used to optimize the variables Carbon and Nitrogen concentration. Characterization of RLs produced occurred by LC-MS. In this study, variables in the quadratic forms and the interaction between them influenced the response (p < 0.05). The most significant variable was N concentration. Maximum RLs yield achieved 39.97 g/L, predominantly of mono-RL. Characterization analysis revealed 9 homologues including the presence of RhaC10C14:2 (m/z 555) whose structure has not previously been observed. This research showed that guava seed oil is an alternative potential carbon source for rhamnolipid production with rare rhamnolipid homologues.

Production and Characterization of Rhamnolipids Produced by Pseudomonas aeruginosa DBM 3774: Response Surface Methodology Approach

Rhamnolipids are extensively studied biosurfactants due to their potential in many industrial applications, eco-friendly production and properties. However, their availability for broader application is severely limited by their production costs, therefore the optimization of efficacy of their cultivation gains significance as well as the information regarding the physio-chemical properties of rhamnolipids resulting from various cultivation strategies. In this work, the bioprocess design focused on optimization of the rhamnolipid yield of Pseudomonas aeruginosa DBM 3774 utilizing the response surface methodology (RSM). Six carbon sources were investigated for their effect on the rhamnolipid production. The RSM prediction improved the total rhamnolipid yield from 2.2 to 13.5 g/L and the rhamnolipid productivity from 11.6 to 45.3 mg/L/h. A significant effect of the carbon source type, concentration and the C/N ratio on the composition of the rhamnolipid congeners has been demonstrated for cultivation of P. aeruginosa DBM 3774 in batch cultivation. Especially, changes in presence of saturated fatty acid in the rhamnolipid congeners, ranging from 18.8% of unsaturated fatty acids (carbon source glycerol; 40 g/L) to 0% (sodium citrate 20 g/L) were observed. This demonstrates possibilities of model based systems as basis in cultivation of industrially important compounds like biosurfactants rhamnolipids and the importance of detailed study of interconnection between cultivation conditions and rhamnolipid mixture composition and properties.

Rhamnolipids produced under aerobic/anaerobic conditions: Comparative analysis and their promising applications

This research comprises a comparative study of the properties, rhl genes expression, and structural difference in rhamnolipids produced under different oxygen conditions via Pseudomonas sp. CH1. The critical micelle concentration (CMC) of rhamnolipids produced under aerobic conditions (RAO) was 100 mg/L. In contrast, rhamnolipids produced under anaerobic conditions (RNO) had a low CMC of 40 mg/L. RNO comprised six rhamnolipids homologs, and the proportion of mono-rhamnolipids was up to 87.83%; meanwhile, the percent ratio of di-rhamnolipids and mono-rhamnolipids in RAO was 63.1:36.9. Additionally, diversified applications for solubilization of hydrophobic pollutants and reduction in heavy oil viscosity were investigated. The addition of RNO greatly enhanced the solubility of phenanthrene in water, from 1.29 mg/L to 193.14 mg/L, a 148.7-fold increase. Moreover, the viscosity of heavy oil decreased by over 90% for both kinds of rhamnolipids, whereas RAO effectively reduced the viscosity even at a low temperature (10 °C). The findings of this study provide insights into the versatile potential applications of rhamnolipids produced under different oxygen conditions.

Effect of rhamnolipids on the fungal elimination of toluene vapor in a biotrickling filter under stressed operational conditions

The application of rhamnolipids in a fungal-cultured biotrickling filter (BTF) has a significant impact on toluene removal. Two BTFs were used; BTF-A, a control bed, and BTF-B fed with rhamnolipids. The effect of empty bed residence times (EBRTs) on toluene bioavailability was investigated. Removal of toluene was carried out at EBRTs of 30 and 60 s and inlet loading rates (LRs) of 23-184 g m^-3 h^-1. At 30 s EBRT, when inlet LR was increased from 23 to 184 g m^-3 h^-1, the removal efficiency (RE) decreased from 93% to 50% for the control bed, and from 94% to 87% for BTF-B. Increasing the EBRT simultaneously with inlet LRs, confirms that BTF-A was diffusion-limited by registering a RE of 62% for toluene inlet LR of 184 g m^-3 h^-1, whereas BTF-B, achieved RE > 96%, confirming a significant improvement in toluene biodegradability. Overall, the best performance was observed at 60 s EBRT and inlet LR of 184 g m^-3 h^-1, providing a maximum elimination capacity (EC) of 176.8 g m^-3 h^-1 under steady-state conditions. While a maximum EC of 114 g m^-3 h^-1 was observed under the same conditions in the absence of rhamnolipids (BTF-A). Measurements of critical micelle concentration showed that 150 mg L^-1 of rhamnolipids demonstrated the lowest aqueous surface tension and maximum formation of micelles, while 175 mg L^-1 was the optimum dose for fungal growth. Production rate of carbon dioxide, and dissolved oxygen contents highlighted the positive influence of rhamnolipids on adhesive forces, improved toluene mineralization, and promotion of microbial motility over mobility.

Bio-cleaning Efficiency of Rhamnolipids Produced from Native Pseudomonas aeruginosa Grown on Agro-industrial By-products for Liquid Detergent Formulation

The cleaning activity of surface-active agents such as rhamnolipids (RLs) requires utmost effectiveness and is employed abundantly in various industries, particularly laundry cleaning, detergents, and cosmetics. In the current study, RLs were produced from Pseudomonas aeruginosa isolated from oil-contaminated soil using a minimal medium amended with agro-industrial by-products of refinery vegetable oil wastes (comprising of unsaturated types of fatty acids as determined by GC analysis) and dairy whey. The results showed that an amount of 5.72 g/L of RLs were obtained, while lower concentrations were obtained using chemically defined carbon sources. Ten congeners of mono- and di-RLs were detected by LC-MS, and they reduced the surface tension of water to 26 mN/m with a critical micelle concentration of 33 mg/L. Furthermore, the produced RLs showed promising cleaning and detergency properties in the removal of different stains on tested fabrics with a Stain Removal Index (SRI) of 17.45%. Moreover, an efficient cleaning was obtained when RLs were applied to a liquid detergent formulation model, and a cleaning power (∆E) of 245.95 and SRI of 36.28% were achieved. The present work showed that the produced RLs could be exploited as a powerful and alternative eco-friendly cleaning agent in many industries.

Characterization of Enterobacter cloacae BAGM01 Producing a Thermostable and Alkaline-Tolerant Rhamnolipid Biosurfactant from the Gulf of Mexico

The search for novel biosurfactants (Bs) requires the isolation of microorganisms from different environments. The Gulf of Mexico (GoM) is a geographical area active in the exploration and exploitation of hydrocarbons. Recent metagenomic and microbiologic studies in this area suggested a potential richness for novel Bs microbial producers. In this work, nineteen bacterial consortia from the GoM were isolated at different depths of the water column and marine sediments. Bs production from four bacterial consortia was detected by the CTAB test and their capacity to reduce surface tension (ST), emulsion index (EI₂₄), and hemolytic activity. These bacterial consortia produced Bs in media supplemented with kerosene, diesel, or sucrose. Cultivable bacteria from these consortia were isolated and identified by bacterial polyphasic characterization. In some consortia, Enterobacter cloacae was the predominant specie. E. cloacae BAGM01 presented Bs activity in minimal medium and was selected to improve its Bs production using a Taguchi and Box-Behnken experimental design; this strain was able to grow and presented Bs activity at 35 g L^-1 of NaCl. This Bs decreased ST to around 34.5 ± 0.56 mNm^-1 and presented an EI₂₄ of 71 ± 1.27%. Other properties of this Bs were thermal stability, stability in alkaline conditions, and stability at high salinity, conferring important and desirable characteristics in multiple industries. The analysis of the genome of E. cloacae BAGM01 showed the presence of rhlAB genes that have been reported in the synthesis of rhamnolipids, and alkAB genes that are related to the degradation of alkanes. The bioactive molecule was identified as a rhamnolipid after HPLC derivatization, ¹H NMR, and UPLC-QTOF-MS analysis.

Recent progress and trends in the analysis and identification of rhamnolipids

Rhamnolipids have extensive potential applications and are the most promising biosurfactants for commercialization. The efficient and accurate identification and analysis of these are important to their production, application and commercialization. Accordingly, significant efforts have been made to identify and analyse rhamnolipids during screening of producing strains, fermentation and application processes. Cationic cetyltrimethylammonium bromide-methylene blue (CTAB-MB) test combines a series of indirect assays to efficiently assist in the primary screening of rhamnolipids-producing strains, while the secretion of rhamnolipids by these strains can be identified through TLC, FTIR, NMR, electrospray ionization mass spectrometry (ESI-MS) and HPLC-MS analysis. Rhamnolipids can be quantified by colorimetric methods requiring the use of concentrated acid, and this approach has the advantages of reliability, simplicity, low-cost and excellent reproducibility with very low technological requirements. HPLC-MS can also be employed as required as a more accurate quantification method. In addition, HPLC-ELSD has been established as the internationally acceptable measure of rhamnolipids for commercial purposes. The preparation of well-accepted rhamnolipids standards and modifications of analysis operations are essential to further enhance the accuracy and improve the simplicity of rhamnolipid analysis.Key points• Current status of R&D works on determination of rhamnolipids is listed• Advantages and disadvantages of various types analysis are summarized• Limitations of current rhamnolipid quantification are discussed Graphical abstract.

Remediation of Aviation Kerosene-Contaminated Soil by Sophorolipids from Candida bombicola CB 2107

Yeast-derived biosurfactants may substitute or complement chemical surfactants as green reagents to extract petroleum hydrocarbons from contaminated soil. The effectiveness of contaminant clean-up by sophorolipids was tested on kerosene-contaminated soil with reference to traditional synthetic surfactants. The sophorolipids produced by the yeast Candida bombicola CB 2107, cultivated with the carbon sources 10 g/L glucose and 10 g/L rapeseed oil, were most effective in contaminant removal. This biosurfactant revealed a critical micelle concentration of 108 mg/L which was close to that of Triton X-100 (103 mg/L), the synthetic surfactant considered as reference. It outperformed Triton X-100 in reducing kerosene concentrations (C10–C40) in contaminated soils. In a soil initially containing 1080 mg/kg of C10–C40, the concentration was reduced to 350 mg/kg using the biosurfactant, and to 670 mg/kg using Triton-X. In the soil with initial concentration of 472 mg/kg, concentrations were reduced to 285 and 300 mg/kg for biosurfactant and Triton X-100, respectively. Sophorolipids have the potential to replace synthetic surfactants. Properties and performance of the biosurfactants, however, strongly differ depending on the yeast and the growing conditions during production.

High Di-rhamnolipid Production Using Pseudomonas aeruginosa KT1115, Separation of Mono/Di-rhamnolipids, and Evaluation of Their Properties

Rhamnolipids (RLs) are important bioproducts that are regarded as promising biosurfactant for applications in oil exploitation, cosmetics, and food industry. In this study, the newly isolated Pseudomonas aeruginosa KT1115 showed high production of di-RLs. The highest yield of RLs by P. aeruginosa KT1115, reaching 44.39 g/L after 8 days of fermentation in a 5 L bioreactor, was obtained from rapeseed oil-nitrate medium after process optimization. Furthermore, we established a new separation process that achieved up to 91.82% RLs recovery with a purity of 89% and further obtained mono/di-rhamnolipids. Finally, ESI-MS analysis showed that the RLs produced by strain KT1115 have a high proportion of di-RLs (mono-RLs: di-RLs = 11.47: 88.53), which have a lower critical micelle-forming concentration (8 mN/m) and better emulsification ability with kerosene (52.1% EI₂₄) than mono-RLs (167 mN/m and 41.4% EI₂₄, respectively). These results demonstrated that P. aeruginosa KT1115 is a potential industrial producer of di-RLs, which have improved applicability and offer significant commercial benefits.

Desorption and solubilization of anthracene by a rhamnolipid biosurfactant from Rhodococcus fascians

The rhamnolipid biosurfactant-producing bacterium, strain SDRB-G7, was isolated from the sediment of Sindu-ri beach and identified as Rhodococcus fascians based on a phylogenetic analysis. Optimal activity, with the highest yield (2.441 g/L) and surface tension-reducing activity (24.38 mN/m), was observed when the cells were grown on olive oil as their sole source of carbon at pH 8.0. The rhamnolipid biosurfactant showed environmental stability at a variety of NaCl concentrations (2-20%) and pH values (2-12) even under acidic conditions. Of the initial anthracene, 66% was solubilized by 100% crude biosurfactant. Furthermore, 100% crude biosurfactant desorbed 81% of the anthracene in sediment into the aqueous phase. These results suggest that the rhamnolipid biosurfactant produced from R. fascians SDRB-G7 is a promising candidate for polycyclic aromatic hydrocarbon (PAH) removal from the sediment and can be an effective agent for processes that bioremediate PAHs such as surfactant-enhanced remediation. PRACTITIONER POINTS: Biosurfactants can accelerate desorption of PAHs and improve their solubility. BS-producing R. fascians SDRB-G7 was selected by screening of biochemical tests. Solubility of anthracene was enhanced by rhamnolipid produced by strain SDRB-G7. Microbial surfactant is a promising alternative for bioremediation of PAH-polluted sites.

Hyperthermophilic Clostridium sp. N-4 produced a glycoprotein biosurfactant that enhanced recovery of residual oil at 96 °C in lab studies

Biosurfactant producing hypethermophilic microorganisms are essentially required for Microbial Enhanced Oil Recovery (MEOR) from high temperature oil reservoirs (above 90 °C). In the present study, biosurfactant producing Clostridium sp. N-4, optimally growing at 96 °C was isolated from a high temperature oil reservoir. Effect of pH, temperature and salinity on production and activity of N-4 biosurfactant was investigated. Biosurfactant produced by N-4 was partially purified by acid precipitation, characterized using FT-IR spectroscopy; and evaluated for its ability to enhance oil recovery in sand pack studies. The strain N-4 produced biosurfactant over a wide range of pH (5.0-9.0) and salinity (0-13%) at high temperature (80-100 °C) and optimally at pH 7, 96 °C and 4% salinity. N-4 biosurfactant was active at 37-101 °C; pH, 5-10 and salinity of 0-12 % (w/v). N-4 biosurfactant, characterized as glycoprotein reduced the surface tension of water by 32 ± 0.4 mN/m at critical micelle concentration of 100 μg/ml. N-4 biosurfactant mobilized 17.15% of residual oil saturation in sand pack studies. Similarly, the strain N-4 also recovered 36.92% of the residual oil in sand pack studies under the conditions mimicking the environment of depleted high temperature oil reservoir. Thus, the biosurfactant producing Clostridium sp. N-4 was identified as a suitable agent for enhanced oil recovery from high temperature oil reservoirs.

Cytotoxic effects of mono- and di-rhamnolipids from Pseudomonas aeruginosa MR01 on MCF-7 human breast cancer cells

Rhamnolipids produced by P. aeruginosa MR01 were fractionated into mono- and di-rhamnolipids, and their dominant congeners, Rha-C₁₀-C₁₀ and Rha-Rha-C₁₀-C₁₀, were shown by mass spectrometry. Minimum surface tensions and critical micelle concentrations (CMC) were determined as "≃34 mN/m; ≃26.17 mg/l;" and "≃29 mN/m; ≃29.63 mg/l" for mono- and di-rhamnolipids, respectively. Spectrophotometry measurements provided a close approximation of CMC. Contact angle and diameter of wet area were determined for rhamnolipid-containing drops on hydrophobic paper to display their capability for alteration of surface wettability. Wet area measurement is a simple, reliable method not requiring a Drop Shape Analyzer. Cell viabilities determined by MTT assay showed a decline in a dose-dependent manner and estimated IC₅₀ values were 25.87 μg/ml and 31.00 μg/ml for mono- and di-rhamnolipids treating MCF-7 cells for 48 h. Morphological observations using the inverted phase-contrast microscopy and fluorescence microscopy via Hoechst staining revealed the apoptotic characteristics in treated MCF-7 cells. The semi-quantitative RT-PCR method demonstrated that expression of the p53 gene in mRNA levels significantly (P < 0.05) increased when treated with 30 μg/ml of each rhamnolipid compound for 12 h. It can be concluded that rhamnolipids derived from MR01 show significant anticancer potential against MCF-7 cell line and should be further investigated as natural, therapeutic anti-tumor agents.

High-Yield Di-Rhamnolipid Production by Pseudomonas aeruginosa YM4 and its Potential Application in MEOR

Rhamnolipids are a mixture of the homologs species due to variations in the rhamnose units and β-hydroxy fatty acid moieties, mainly including Rha-C10-C10, Rha-Rha-C10-C10, and Rha-C10. In this study, strain P. aeruginosa YM4 was selected for its capacity to efficiently produce di-rhamnolipid (Rha-Rha-C10-C10) as the predominant component with soybean oil and glycerol as carbon source, accounting for 64.8% and 85.7% of total products, respectively. The critical micelle concentration (CMC) of rhamnolipid products varies with the content of di-rhamnolipid, whereby lower CMC values corresponding to higher di-rhamnolipid contents. The rhamnolipids containing 85.7% di-rhamnolipid had the lowest CMC value of 50 mg/L. Accordingly the viscosity-reducing efficiency and oil-washing efficiency of rhamnolipids increased with higher di-rhamnolipid component. At a concentration of 500 mg/L, the rhamnolipids containing 85.7% di-rhamnolipid worked best and showed 82.5% oil-washing efficiency, which offered great promise for applications in enhanced oil recovery. The results showed the variation of structure and composition of rhamnolipids had a significant effect on their application.

A novel rhamnolipid-producing Pseudomonas aeruginosa ZS1 isolate derived from petroleum sludge suitable for bioremediation

Petroleum pollutants emulsified by biosurfactants facilitate uptake and biodegradation by environmental microbes. In this report, we show the characterization of an indigenous surfactant-producing crude-oil-eating microbe isolated from petroleum-sludge in Zhoushan islands, China, where one of the national strategic petroleum reservoirs is located. We examined biosurfactant activities using surface tension analysis on mixed culture originated from oil-sludge microbes. In parallel, dynamics of individual microbial populations in cultures were monitored using the terminal fluorescence labeled (TFL)-RFLP method. Biosurfactant activity was found to be associated with a dominant microbial species designated as ZS1 (Zhou-Shan isolate 1). Cell-free supernatant from the ZS1 culture exhibited 100% emulsification index against crude oil and reduces surface tension to 26.5 mN/m. Sequence-based analysis suggested that the ZS1 belongs to the group of Pseudomonas aeruginosa. LC–MS/MS analysis indicated that the rhamnolipids produced by the ZS1 consisted of 7 monorhamnolipid and 11 dirhamnolipid homologues (RL7-11), two of which were novel. Maximum yield of rhamnolipids in shake-flask ZS1 culture could reach 44 g/l. Furthermore, we showed that ZS1 was capable of growing in MS medium supplemented with 1% crude oil as sole carbon source, in which cell mass increase coincided with the formation of crude-oil emulsion. Half of the crude oil was consumed by the ZS1 in 12 days. Taken together, our results show that ZS1 produces high level of rhamnolipids that effectively emulsify crude oil accelerating its uptake and degradation. Hence, it is suitable for bioremediation of petroleum pollutants in Zhoushan coastal areas.

Simultaneous valorization and biocatalytic upgrading of heavy vacuum gas oil by the biosurfactant-producing Pseudomonas aeruginosa AK6U

Heavy vacuum gas oil (HVGO) is a complex and viscous hydrocarbon stream that is produced as the bottom side product from the vacuum distillation units in petroleum refineries. HVGO is conventionally treated with thermochemical process, which is costly and environmentally polluting. Here, we investigate two petroleum biotechnology applications, namely valorization and bioupgrading, as green approaches for valorization and upgrading of HVGO. The Pseudomonas aeruginosa AK6U strain grew on 20% v/v of HVGO as a sole carbon and sulfur source. It produced rhamnolipid biosurfactants in a growth-associated mode with a maximum crude biosurfactants yield of 10.1 g l-1 , which reduced the surface tension of the cell-free culture supernatant to 30.6 mN m-1 within 1 week of incubation. The rarely occurring dirhamnolipid Rha-Rha-C12 -C12 dominated the congeners' profile of the biosurfactants produced from HVGO. Heavy vacuum gas oil was recovered from the cultures and abiotic controls and the maltene fraction was extracted for further analysis. Fractional distillation (SimDist) of the biotreated maltene fraction showed a relative decrease in the high-boiling heavy fuel fraction (BP 426-565 °C) concomitant with increase in the lighter distillate diesel fraction (BP 315-426 °C). Analysis of the maltene fraction revealed compositional changes. The number-average (Mn) and weight-average (Mw) molecular weights, as well as the absolute number of hydrocarbons and sulfur heterocycles were higher in the biotreated maltene fraction of HVGO. These findings suggest that HVGO can be potentially exploited as a carbon-rich substrate for production of the high-value biosurfactants by P. aeruginosa AK6U and to concomitantly improve/upgrade its chemical composition.

Rhamnolipid CMC prediction

Relationships between the purity, pH, hydrophobicity (logK_ow) of the carbon substrate, and the critical micelle concentration (CMC) of rhamnolipid type biosurfactants (RL) were investigated using a quantitative structure-property relationship (QSPR) approach and are presented here for the first time. Measured and literature CMC values of 97 RLs, representing biosurfactants at different stages of purification, were considered. An arbitrary scale for RLs purity was proposed and used in the modelling. A modified evolutionary algorithm was used to create clusters of equations to optimally describe the relationship between CMC and logK_ow, pH and purity (the optimal equation had an R² of 0.8366). It was found that hydrophobicity of the carbon substrate used for the biosynthesis of the RL had the most significant influence on the final CMC of the RL. Purity of the RLs was also found to have a significant impact, where generally the less pure the RL the higher the CMC. These results were in accordance with our experimental data. Therefore, our model equation may be used for controlling the biosynthesis of biosurfactants with properties targeted for specific applications.

Biosurfactants and surfactants interacting with membranes and proteins: Same but different?

Biosurfactants (BS) are surface-active molecules produced by microorganisms. For several decades they have attracted interest as promising alternatives to current petroleum-based surfactants. Aside from their green profile, they have remarkably low critical micelle concentrations, reduce the air/water surface tension to very low levels and are excellent emulsifiers, all of which make them comparable or superior to their synthetic counterparts. These remarkable physical properties derive from their more complex chemical structures in which hydrophilic and hydrophobic regions are not as clearly separated as chemical surfactants but have a more mosaic distribution of polarity as well as branched or circular structures. This allows the lipopeptide surfactin to adopt spherical structures to facilitate dense packing at interfaces. They are also more complex. Glycolipid BS, e.g. rhamnolipids (RL) and sophorolipids, are produced biologically as mixtures which vary in the size and saturation of the hydrophobic region as well as modifications in the hydrophilic headgroup, such as the number of sugar groups and different levels of acetylation, leading to variable surface-active properties. Their amphiphilicity allows RL to insert easily into membranes at sub-cmc concentrations to modulate membrane structure and extract lipopolysaccharides, leading to extensive biofilm remodeling in vivo, sometimes in collaboration with hydrophobic RL precursors. Thanks to their mosaicity, even anionic BS like RL only bind weakly to proteins and show much lower denaturing potency, even supporting membrane protein refolding. Nevertheless, they can promote protein degradation by proteases e.g. by neutralizing positive charges, which together with their biofilm-combating properties makes them very promising detergent surfactants. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.

Strategies for improved rhamnolipid production by Pseudomonas aeruginosa PA1

Rhamnolipids are biosurfactants with potential for diversified industrial and environmental uses. The present study evaluated three strategies for increasing the production of rhamnolipid-type biosurfactants produced by Pseudomonas aeruginosa strain PA1. The influence of pH, the addition of P. aeruginosa spent culture medium and the use of a fed-batch process were examined. The culture medium adjusted to pH 7.0 was the most productive. Furthermore, the pH of the culture medium had a measurable effect on the ratio of synthesized mono- and dirhamnolipids. At pH values below 7.3, the proportion of monorhamnolipids decreased from 45 to 24%. The recycling of 20% of the spent culture medium in where P. aeruginosa was grown up to the later stationary phase was responsible for a 100% increase in rhamnolipid volumetric productivity in the new culture medium. Finally, the use of fed-batch operation under conditions of limited nitrogen resulted in a 3.8-fold increase in the amount of rhamnolipids produced (2.9 g L(-1)-10.9 g L(-1)). These results offer promising pathways for the optimization of processes for the production of rhamnolipids.

Rhamnolipid Adsorption in Soil: Factors, Unique Features, and Considerations for Use as Green Antizoosporic Agents

In aqueous solutions, rhamnolipids effectively kill the motile zoospores responsible for spreading many pathogens, including soy-infecting Phytophthora sojae. For use in soil, adsorption properties need to be considered. Having low critical micelle concentrations, rhamnolipids tend to form micelles/aggregates with unknown effects on soil adsorption. Effects of soil pH, rhamnolipid congener structure, and concentration were examined. Congeners were identified and each quantitated for adsorptive partitioning. The adsorption isotherm at pH 6.5 showed a multi-stage profile plateauing at 1700 μg/g of soil. Less hydrophilic congeners adsorbed preferentially: R-C10-C12 > R-C10-C12:1 > RR-C10-C12:1 > RR-C10-C12 > R-C10-C10 > RR-C10-C10 > R-C8-C10 > RR-C8-C10 (where R is rhamnose and C# is the carbon number of β-hydroxy fatty acid). Adsorptive selectivity among congeners was very clear in dilute solutions but diminished with increasing concentrations. Results were interpreted with aggregate formation in solutions and on the soil surface. The cost estimate made accordingly supported the economic feasibility of rhamnolipid antizoosporic uses in soil.

Sorption/desorption behavior of triclosan in sediment-water-rhamnolipid systems: Effects of pH, ionic strength, and DOM

Effects of pH, ionic strength and DOM on the sorption and desorption of triclosan (TCS) in sediment-water-rhamnolipid systems were systematically investigated through controlled batch experiments. Results showed that solubilization enhancement of TCS by rhamnolipid was higher in acid pH range than in alkaline pH range and was the highest at the ionic strength of 5×10(-2) M. Sorption of rhamnolipid onto sediment decreased with the increase of pH while the result was contrary to ionic strength. Moreover, the apparent distribution coefficients of TCS (Kd(*)) decreased from 73.35 to 32.30 L/kg with an increase of solution pH, as varying pH had significant influence on sorption of RL onto sediment and degree of ionization of TCS. Rhamnolipid presented the largest distribution capacity of TCS into the aqueous phase at moderate ionic strength (5×10(-2) M) with the Kd(*) of 17.26 L/kg. Further results also indicated that the presence of humic acid in aqueous phase could increase the desorption of TCS from contaminated sediment. The desorption enhancement was much higher in the system containing both rhamnolipid and DOM than in the single system. These findings provide meaningful information for enhanced migration of TCS from sediment to water by rhamnolipid.

Biosurfactant production by Pseudomonas aeruginosain kefir and fish meal

The aim of this study was to increase rhamnolipid production by formulating media using kefir and fish meal for Pseudomonas aeruginosa strains isolated from different environmental resources. The strains, named as H1, SY1, and ST1, capable of rhamnolipid production were isolated from soil contaminated with wastes originating from olive and fish oil factories. Additionally, P. aeruginosa ATCC 9027 strain, which is known as rhamnolipid producer, was included in the study. Initially, rhamnolipid production by the strains was determined in Mineral Salt Medium (MSM) and then in media prepared by using kefir and fish meal. The obtained rhamnolipids were purified and quantified according to Dubois et al. (1956). The quantity of rhamnolipids of ATCC, H1 and SY1 strains in kefir media were determined as 11.7 g/L, 10.8 g/L and 3.2 g/L, respectively, and in fish meal media as 12.3 g/L, 9.3 g/L and 10.3 g/L, respectively. In addition, effect of UV light exposure on rhamnolipid production was also investigated but contrary a decrease was observed. The results indicate that P. aeruginosa strains isolated from various environmental resources used in this study can be important due to their rhamnolipid yield, and fish meal, which is obtained from waste of fish, can be an alternative source in low cost rhamnolipid production.

Stimulation of rhamnolipid biosurfactants production in Pseudomonas aeruginosa AK6U by organosulfur compounds provided as sulfur sources

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Organosulfur compounds promote biosurfactants production when provided as sulfur sources.

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Quantitative and qualitative changes in biosurfactants production depending on the sulfur source.

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Simultaneous production of biosurfactants and biodesulfurization.

A Pseudomonas aeruginosa AK6U strain produced rhamnolipid biosurfactants to variable extents when grown on MgSO₄ or organosulfur compounds as sulfur sources and glucose as a carbon source. Organosulfur cultures produced much higher biosurfactants amounts compared to the MgSO₄ cultures. The surface tension of the growth medium was reduced from 72 mN/m to 54 and 30 mN/m in cultures containing MgSO₄ and 4,6-dimethyldibenzothiophene (4,6-DM-DBT), respectively. AK6U cultures produced different rhamnolipid congener profiles depending on the provided sulfur source. The dibenzothiophene (DBT) culture produced more diverse and a higher number of rhamnolipid congeners as compared to the DBT-sulfone and MgSO₄ cultures. The number of mono-rhamnolipid congeners in the DBT culture was also higher than that detected in the DBT-sulfone and MgSO₄ cultures. Di-rhamnolipids dominated the congener profiles in all the analyzed cultures. The sulfur source can have a profound impact on the quality and quantity of the produced biosurfactants.

Identification of lipopeptide isoforms by MALDI-TOF-MS/MS based on the simultaneous purification of iturin, fengycin, and surfactin by RP-HPLC

A three-stage linear gradient strategy using reverse-phase high-performance liquid chromatography (HPLC) was optimized for rapid, high-quality, and simultaneous purification of the lipopeptide isoforms of iturin, fengycin, and surfactin, which may differ in composition by only a single amino acid and/or the fatty acid residue. Matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS) was applied to detect the lipopeptides harvested from each reversed-phase HPLC peak. Amino acid analysis based on phenyl isothiocyanate derivatization was further used for confirmation of the amino acid species and molar ratio in a certain HPLC fraction. By this MALDI-TOF-MS/MS coupled with amino acid analysis, it was revealed that iturin at m/z 1,043 consists of a circular Asn-Tyr-Asn-Gln-Pro-Asn-Ser peptide and C14 β-OH fatty acid. Surfactin homologs from Bacillus subtilis THY-7 at m/z 1,030, 1,044, 1,058, and 1,072 possess a circular Glu-Leu-Leu-Val-Asp-Leu-Leu peptide and the β-OH fatty acid with a different length (C13-C16). Fengycin species at m/z 1,463 and 1,477 are homologs possessing the circular peptide Glu-Orn-Tyr-Thr-Glu-Ala-Pro-Gln-Tyr-Ile linked to a C16 or C17 γ-OH fatty acid, whereas fengycin at m/z 1,505 contains a Glu-Orn-Tyr-Thr-Glu-Val-Pro-Gln-Tyr-Ile sequence with a Val instead of Ala at position 6. The method developed in this work provided an efficient approach for characterization of diverse lipopeptide isoforms from the iturin, fengycin, and surfactin families.

Rhamnolipids Production by a Pseudomonas eruginosa LBI Mutant: Solutions and Homologs Characterization

This paper evaluates the effect of additives (NaCl and ethanol) on the solution properties of rhamnolipids. The properties are the surface activity, aggregate formations and emulsifying activity as well as the synergistic effects of additives and pH variations on the physical properties of rhamnolipids. Additionally, analysis of fatty acids and rhamnolipid homologues produced using different carbon sources was performed by mass spectrometry. The results indicate that this biosurfactant maintain its properties in the presence of additives. NaCl decreases the size and number of aggregates formed in solutions without pH control, while ethanol to rhamnolipid solutions reduces critical micelle concentration and favors aggregation of monomers. The profiles of fatty acids produced by P. aeruginosa LBI 2A1 varied according to the carbon source used, however for rhamnolipids there was no difference.

Rhamnolipids elicit the same cytotoxic sensitivity between cancer cell and normal cell by reducing surface tension of culture medium

Biosurfactant rhamnolipids have been claimed to show biological activities of inhibiting the proliferation of cancer cells. In this study, the cytotoxicity of rhamnolipids was examined on four cancer cells (HepG2, Caco-2, Hela, MCF-7 cells) and two normal cells (HK-2 cell, primary hepatocyte). Interestingly, both cancer cells and normal cells exhibited similar sensitivities to the addition of rhamnolipids in culture medium, and the cytotoxicity was largely attenuated by the presence of fetal bovine serum (FBS) in culture medium. In correlation of the mono-/di-rhamnolipid cytotoxicity with the surface tension of culture medium, it was found that rhamnolipids triggered cytotoxicity whenever the surface tension of culture medium decreased below 41 mN/m irrespective of the FBS content in culture medium, cell line, or rhamnolipid congener. Similarly, each chemical surfactant (Tween-80, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate) could cause cytotoxicity on HepG2 cells whenever its addition made the surface tension under 41 mN/m in culture medium with or without the presence of FBS. It seems that rhamnolipids, like chemical surfactants, exhibited cytotoxicity by reducing the surface tension of culture medium rather than by changing its specific molecular structure, which had no selection on tumor cells. This study could offer helps to correct the misleading biological activity of rhamnolipids and to avoid the possible large wastes of time and expenses on developing the applications in antitumor drugs.

Quantitative analyses of the isoforms of surfactin produced by Bacillus subtilis HSO 121 using GC-MS

Lipopeptide is one of the most important biosurfactants. The content of each isoform of a lipopeptide is crucial to the study of the properties of metabolites as well as the biological and biochemical characters of microbes. However, this information has not been accurately provided by the current analysis method. A new method for the quantitative determination of each isoform in the surfactin family has been established. The surfactin was firstly hydrolyzed in an acid solution at 90°C for 20 h, dried and then treated with bis(trimethylsilyl)trifluoroacetamide at 60°C for 20 min. The derived hydrolysates were then analyzed by GC-MS for a quantitative determination via comparison with working curves made with amino acids. GC-MS analyses show that the nine isoforms with an amount of 4.80 × 10(-7) mol (493 µg) in a 500 µg surfactin sample were detected, in which the mole fractions of surfactin isoforms with different fatty acid chains were 0.32% (n C(12)), 4.89% (iso C(13)), 6.27% (anteiso C(13)), 23.05% (iso C(14)), 8.95% (n C(14)), 17.69% (iso C(15)), 38.69% (anteiso C(15)), 0.07% (iso C(16)), and 0.07% (n C(16)), respectively. This approach can be applied to quantitative analyses for other families of lipopeptides as long as the sequence of amino acid residues in the peptide is determined.