Kinetic studies on surfactant production byPseudomonas aeruginosa 44T1

Recent progress towards industrial rhamnolipids fermentation: Process optimization and foam control

The global market for rhamnolipids production holds great promise, and is in need of an economically viable mass-production scheme. Accordingly, several strategies have been employed to improve the efficiency of rhamnolipid production in the past few decades. Currently, rhamnolipids can be produced by Pseudomonas aeruginosa at a high yield (over 70 g/L) when vegetable oil is used as the carbon source under optimized fed-batch cultivations. However, severe foaming during rhamnolipid fermentation inhibits scaling-up and production efficiency. Stop valve was found to effective break the extremely stable rhamnolipids foams during fermentation, and production efficiency of rhamnolipids was highly improved, while its scale-up mechanism needs further study. In addition, the combination of both chemical and mechanical approaches is likely to be more efficiently resolving the foam problem existed in rhamnolipids fermentation than either chemical or mechanical methods alone.

Maximize rhamnolipid production with low foaming and high yield

Rhamnolipids are well-known microbial surfactants with many potential applications. Their production cost, however, remains high due to the severe foaming tendency in aerobic fermentation and the relatively low productivity and yield. In this study, we assessed the boundaries set by these constraints after optimization of basic parameters such as dissolved oxygen concentration (DO), pH and carbon sources. DO 10% and pH 5.5-5.7 were found optimal; cell growth and/or rhamnolipid production were slower at lower DO (5%) or pH (5.0) while foaming became hard to control at higher DO (30%) or pH (6.0 and 6.5). Although the Pseudomonas aeruginosa strain used was selected for its high rhamnolipid production from glycerol as substrate, soybean oil was still found to be a better substrate that increased specific rhamnolipid productivity to 25.8mg/g cells-h from the glycerol-supported maximum of 8.9mg/g cells-h. In addition, the foam volume was approximately halved by using soybean oil instead of glycerol as substrate. Analysis by liquid chromatography coupled with mass spectrometry revealed that rhamnolipid compositions from the two carbon sources were also very different, with primarily (82%) monorhamnolipids from soybean oil and more (64%) dirhamnolipids from glycerol. The optimized fermentation produced 42g/l rhamnolipids at a yield of approximately 47% and a volumetric productivity of 220mg/l-h. These values are among the highest reported.

Enhancement of Biosurfactant Production from Pseudomonas cepacia CCT6659 Through Optimisation of Nutritional Parameters Using Response Surface Methodology

The aim of the present study was to optimise the production of a biosurfactant by a new strain of Pseudomonas cepacia CCT6659 with aid of a combination of central composite rotatable design (CCRD) and response surface methodology (RSM). The factors selected for optimisation of the growth conditions were canola waste frying oil, corn steep liquor and NaNO3 substrate concentrations. Surface tension was chosen as the response variable. All factors studied were important within the ranges investigated. The empirical forecast model developed through RSM regarding effective nutritional factors was adequate for explaining 89 % of the variation observed in biosurfactant production. Maximal reduction in surface tension of 26 mN m–1 was obtained under the optimal conditions of 2 % waste frying oil, 3 % corn steep liquor and 0.2 % NaNO3. The accumulation of isolated biosurfactant increased from 2 g L–1 to 8.0 g L–1 under these conditions, demonstrating that the factorial design is adequate for identifying the optimal conditions for biosurfactant production.

Optimization of Nutrient Requirements and Culture Conditions for the Production of Rhamnolipid from Pseudomonas aeruginosa (MTCC 7815) using Mesua ferrea Seed Oil

Environmental awareness has led to a serious consideration for biological surfactants and hence non-edible vegetable oils may serve as a substitute carbon source for bio-surfactant production (rhamnolipid) which might be an alternative to complex synthetic surfactants. There are reports of rhamnolipid production from plant based oil giving higher production than that of glucose because of their hydrophobicity and high carbon content. Therefore the contribution of non-edible oil such as Mesua ferrea seed oil could serve as a good carbon source for rhamnolipid production. Moreover the use of rhamnolipid production from non-edible plant based seed oil has not been reported elsewhere. The present work focus on the optimal production of rhamnolipid by considering both micro and macro nutrients and culture conditions using response surface methodology. The study observes that micronutrients play a significant role in rhamnolipid production from Pseudomonas aeruginosa (MTCC 7815). The investigation results with the statistically optimize parameters able to produce a higher rhamnolipid production and this methodology could be used to optimize the nutrients requirements and culture conditions. The present findings would assist in bioremediation of crude oil contaminated ecosystems.

Production and characterization of rhamnolipid biosurfactant from waste frying coconut oil using a novel Pseudomonas aeruginosa D

AIM

To improve biosurfactant production economics by the utilization of potential low-cost materials.

METHODS AND RESULTS

In an attempt to utilize cost-effective carbon sources in the fermentative production of biosurfactants, various pure and waste frying oils were screened by a standard biosurfactant producing strain. Considering the regional significance, easy availability and the economical advantages, waste frying coconut oil was selected as the substrate for further studies. On isolation of more competent strains that could use waste frying coconut oil efficiently as a carbon source, six bacterial strains were isolated on cetyltrimethyl ammonium bromide-methylene blue agar plate, from a soil sample collected from the premises of a coconut oil mill. Among these, Pseudomonas aeruginosa D was selected as the potential producer of rhamnolipid. Spectrophotometric method, TLC, methylene blue active substance assay, drop collapse technique, surface tension measurement by Du Nouy ring method and emulsifying test confirmed the rhamnolipid producing ability of the selected strain and various process parameters were optimized for the production of maximum amount of biosurfactant. Rhamnolipid components purified and separated by ethyl acetate extraction, preparative silica gel column chromatography, HPLC and TLC were characterized by fast atom bombardment mass spectrometry as a mixture of dirhamnolipids and monorhamnolipids. The rhamnolipid homologues detected were Rha-Rha-C(10) -C(10) , Rha-C(12) -C(10) and Rha-C(10) -C(8) /Rha-C(8) -C(10) .

CONCLUSION

These results indicated the possibility of waste frying coconut oil to be used as a very effective alternate substrate for the economic production of rhamnolipid by a newly isolated Ps. aeruginosa D.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results of this study throws light on the alternate use of already used cooking oil as high-energy source for producing a high value product like rhamnolipid. This would provide options for the food industry other than the recycling and reuse of waste frying oils in cooking and also furthering the value of oil nuts.

Why do microorganisms produce rhamnolipids?

We review the environmental role of rhamnolipids in terms of microbial life and activity. A large number of previous research supports the idea that these glycolipids mediate the uptake of hydrophobic substrates by bacterial cells. This feature might be of highest priority for bioremediation of spilled hydrocarbons. However, current evidence confirms that rhamnolipids primarily play a role in surface-associated modes of bacterial motility and are involved in biofilm development. This might be an explanation why no direct pattern of hydrocarbon degradation was often observed after rhamnolipids supplementation. This review gives insight into the current state of knowledge on how rhamnolipids operate in the microbial world.

Regulatory and metabolic network of rhamnolipid biosynthesis: traditional and advanced engineering towards biotechnological production

During the last decade, the demand for economical and sustainable bioprocesses replacing petrochemical-derived products has significantly increased. Rhamnolipids are interesting biosurfactants that might possess a broad industrial application range. However, despite of 60 years of research in the area of rhamnolipid production, the economic feasibility of these glycolipids is pending. Although the biosynthesis and regulatory network are in a big part known, the actual incidents on the cellular and process level during bioreactor cultivation are not mastered. Traditional engineering by random and targeted genetic alteration, process design, and recombinant strategies did not succeed by now. For enhanced process development, there is an urgent need of in-depth information about the rhamnolipid production regulation during bioreactor cultivation to design knowledge-based genetic and process engineering strategies. Rhamnolipids are structurally comparable, simple secondary metabolites and thus have the potential to become instrumental in future secondary metabolite engineering by systems biotechnology. This review summarizes current knowledge about the regulatory and metabolic network of rhamnolipid synthesis and discusses traditional and advanced engineering strategies performed for rhamnolipid production improvement focusing on Pseudomonas aeruginosa. Finally, the opportunities of applying the systems biotechnology toolbox on the whole-cell biocatalyst and bioprocess level for further rhamnolipid production optimization are discussed.

Evaluation of rhamnolipid production capacity of Pseudomonas aeruginosa PAO1 in comparison to the rhamnolipid over-producer strains DSM 7108 and DSM 2874

A lack of understanding of the quantitative rhamnolipid production regulation in bioreactor cultivations of Pseudomonas aeruginosa and the absence of respective comparative studies are important reasons for achieving insufficient productivities for an economic production of these biosurfactants. The Pseudomonas strains DSM 7108 and DSM 2874 are described to be good rhamnolipid over-producers. The strain PAO1 on the other hand is the best analyzed type strain for genetic regulation mechanisms in the species P. aeruginosa. These three strains were cultivated in a 30-L bioreactor with a medium containing nitrate and sunflower oil as sole C-source at 30 and 37 °C. The achieved maximum rhamnolipid concentrations varied from 7 to 38 g/L, the volumetric productivities from 0.16 to 0.43 g/(L·h), and the cellular yield from 0.67 to 3.15 g/g, with PAO1 showing the highest results for all of these variables. The molar di- to mono-rhamnolipid ratio changed during the cultivations; it was strain dependent but not significantly influenced by the temperature. This study explicitly shows that the specific rhamnolipid synthesis rate per cell follows secondary metabolite-like courses coinciding with the transition to the stationary phase of typical logistic growth behavior. However, the rhamnolipid synthesis was already induced before N-limitation occurred.

Biosurfactant's role in bioremediation of NAPL and fermentative production

Surfactants and biosurfactants are amphipathic molecules with both hydrophilic and hydrophobic moieties that partition preferentially at the interface between fluid phases that have different degrees of polarity and hydrogen bonding which confers excellent detergency, emulsifying, foaming and dispersing traits, making them most versatile process chemicals. One of the major applications of (bio)surfactants is in environmental bioremediation field. Most synthetic organic compounds present in contaminated soils are only weakly soluble or completely insoluble in water, so they exist in the subsurface as separate liquid phase, often referred as a non-aqueous phase liquids (NAPL), which poses as threat to environment. Several studies have revealed the use of surfactants for remediation; however, several factors limit the use of surfactants in environmental remediation, mainly persistence of surfactants or their metabolites and thus potentially pose an environmental concern. Biosurfactants may provide a more cost-effective approach for subsurface remediation when used alone or in combination with synthetic surfactants. There are several advantages of biosurfactants when compared to chemical surfactants, mainly biodegradability, low toxicity, biocompatibility and ability to be synthesized from renewable feedstock. Despite having many commercially attractive properties and clear advantages compared with their synthetic counterparts, biosurfactants have not yet been employed extensively in industry because of their low yields and relatively high production and recovery costs. However, the use of mutants and recombinant hyperproducing microorganisms along with the use of cheaper raw materials and optimal growth and production conditions and more efficient recovery processes, the production of biosurfactant can be made economically feasible. Therefore, future research aiming for high-level production of biosurfactants must be focused towards the development of appropriate combinations of hyperproducing microbial strains, optimized cheaper production media and optimized process conditions, which will lead to economical commercial level biosurfactant production.

Analysis of rhamnolipid biosurfactants produced through submerged fermentation using orange fruit peelings as sole carbon source

The fermentative production of rhamnolipid biosurfactant from Pseudomonas aeruginosa MTCC 2297 was carried out by submerged fermentation using various cost-effective waste materials such as orange peelings, carrot peel waste, lime peelings, coconut oil cake, and banana waste. The orange peel was found to be the best substrate generating 9.18 g/l of rhamnolipid biosurfactant with a surface tension reduction up to 31.3 mN/m. The production was growth independent, and optimum conditions were standardized. The emulsifying activity was highest against kerosene (73.3%). Rhamnolipid components were purified and separated by ethyl acetate extraction, preparative silica gel column chromatography, high-performance liquid chromatography and thin-layer chromatography. The major rhamnolipid components were characterized, by fast atom bombardment mass spectrometry, as a mixture of dirhamnolipids and monorhamnolipids.

Pseudomonas aeruginosa LBI production as an integrated process using the wastes from sunflower-oil refining as a substrate

Pseudomonas aeruginosa LBI produced surface active rhamnolipids when cultivated on waste from the sunflower-oil process under different conditions. These biosurfactants, which reduce the superficial and interfacial tensions between fluids, offer advantages over their chemical counterparts, especially because of their ecological acceptability. These molecules can be used in fields as diverse as chemical, pharmaceutical and petrochemical industries. In this work, we present the effect of C/N ratio on growth and production yield. The best production yields (Y P/S) were achieved for C/N ratios (in g/g) of 8/1 (0.22) and 6.4/1 (0.23). The product concentration was very satisfactory (7.3g/L) at C/N ratio of 8/1, especially when considering that the substrate was basically composed of wastes that would otherwise constitute an environmental disposal problem.

Optimization of surfactin production by Bacillus subtilis isolate BS5

Bacillus subtilis BS5 is a soil isolate that produces promising yield of surfactin biosurfactant in mineral salts medium (MSM). It was found that cellular growth and surfactin production in MSM were greatly affected by the environmental fermentation conditions and the medium components (carbon and nitrogen sources and minerals). Optimum environmental conditions for high surfactin production on the shake flask level were found to be a slightly acidic initial pH (6.5-6.8), an incubation temperature of 30 degrees C, a 90% volumetric aeration percentage, and an inoculum size of 2% v/v. For media components, it was found that the optimum carbon source was molasses (160 ml/l), whereas the optimum nitrogen source was NaNO(3) (5 g/l) and the optimum trace elements were ZnSO(4).7H(2)O (0.16 g/l), FeCl(3).6H(2)O (0.27 g/l), and MnSO(4).H(2)O (0.017 g/l). A modified MSM (molasses MSM), combining the optimum medium components, was formulated and resulted in threefold increase in surfactin productivity that reached 1.12 g/l. No plasmid could be detected in the tested isolate, revealing that biosurfactant production by B. subtilis isolate BS5 is chromosomally mediated but not plasmid-mediated.

Repeated pH-stat fed-batch fermentation for rhamnolipid production with indigenous Pseudomonas aeruginosa S2

Rhamnolipid is one of the most commonly used biosurfactants with the ability to reduce the surface tension of water from 72 to 30 mN/m. An indigenous isolate Pseudomonas aeruginosa S2 possessing excellent ability to produce rhamnolipid was used as a model strain to explore fermentation technology for rhamnolipid production. Using optimal medium and operating conditions (37 degrees C, pH 6.8, and 250 rpm agitation) obtained from batch fermentation, P. aeruginosa S2 was able to produce up to 5.31 g/l of rhamnolipid from glucose-based medium. To further improve the rhamnolipid yield, a pH-stat fed-batch culture was performed by maintaining a constant pH of 6.8 through manipulating glucose feeding. The effect of influent glucose concentration on rhamnolipid yield and productivity was investigated. Using the pH-stat culture, a maximum rhamnolipid concentration (6.06 g/l) and production rate (172.5 ml/h/l) was obtained with 6% glucose in the feed. Moreover, combining pH-stat culture with fill-and-draw operation allowed a stable repeated fed-batch operation for approximately 500 h. A marked increase in rhamnolipid production was achieved, leading to the best rhamnolipid yield of approximately 9.4 g/l during the second repeated run.

Production of rhamnolipids by Pseudomonas aeruginosa

Pseudomonas aeruginosa produces glycolipidic surface-active molecules (rhamnolipids) which have potential biotechnological applications. Rhamnolipids are produced by P. aeruginosa in a concerted manner with different virulence-associated traits. Here, we review the rhamnolipids biosynthetic pathway, showing that it has metabolic links with numerous bacterial products such as alginate, lipopolysaccharide, polyhydroxyalkanoates, and 4-hydroxy-2-alkylquinolines (HAQs). We also discuss the factors controlling the production of rhamnolipids and the proposed roles this biosurfactant plays in P. aeruginosa lifestyle.

Screening and production of rhamnolipids by Pseudomonas aeruginosa 47T2 NCIB 40044 from waste frying oils

World production of oils and fats is about 2.5 million tonnes, 75% of which are derived from plants. Most of them are used in the food industry for the manufacture of different products, or directly as salad oil. Great quantities of waste are generated by the oil and fat industries: residual oils, tallow, marine oils, soap stock, frying oils. It is well known that the disposal of wastes is a growing problem and new alternatives for the use of fatty wastes should be studied. Used frying oils, due to their composition, have great potential for microbial growth and transformation. The use of economic substrates such as hydrophobic wastes meets one of the requirements for a competitive process for biosurfactant production. In the Mediterranean countries, the most used vegetable oils are sunflower and olive oil. Here we present a screening process is described for the selection of micro-organism strains with the capacity to grow on these frying oils and accumulate surface-active compounds in the culture media. From the 36 strains screened, nine Pseudomonas strains decreased the surface tension of the medium to 34-36 mN/M; the emulsions with kerosene remained stable for three months. Two Bacillus strains accumulated lipopeptide and decreased the surface tension to 32-34 mN/m. Strain Ps. aeruginosa 47T2 was selected for further studies. The effect of nitrogen and a C/N of 8. 0 gave a final production of rhamnolipid of 2.7 g l-1 as rhamnose, and a production yield of 0.34 g g-1.