Applications of microbial surfactants

Biosurfactants are amphiphilic compounds produced by microorganisms that are capable of decreasing surface and interfacial tensions. They are useful in remediation of insoluble organic pollutants in soil and marine environments. There are also a large number of industrial uses for biosurfactants. This paper reviews recent research on applications of microbially-produced surfactants.     

Biodegradability of bacterial surfactants

This work aimed at evaluating the biodegradability of different bacterial surfactants in liquid medium and in soil microcosms. The biodegradability of biosurfactants by pure and mixed bacterial cultures was evaluated through CO₂ evolution. Three bacterial strains, Acinetobacter baumanni LBBMA ES11, Acinetobacter haemolyticus LBBMA 53 and Pseudomonas sp. LBBMA 101B, used the biosurfactants produced by Bacillus sp. LBBMA 111A (mixed lipopeptide), Bacillus subtilis LBBMA 155 (lipopeptide), Flavobacterium sp. LBBMA 168 (mixture of flavolipids), Dietzia Maris LBBMA 191(glycolipid) and Arthrobacter oxydans LBBMA 201(lipopeptide) as carbon sources in minimal medium. The synthetic surfactant sodium dodecyl sulfate (SDS) was also mineralized by these microorganisms, but at a lower rate. CO₂ emitted by a mixed bacterial culture in soil microcosms with biosurfactants was higher than in the microcosm containing SDS. Biosurfactant mineralization in soil was confirmed by the increase in surface tension of the soil aqueous extracts after incubation with the mixed bacterial culture. It can be concluded that, in terms of biodegradability and environmental security, these compounds are more suitable for applications in remediation technologies in comparison to synthetic surfactants. However, more information is needed on structure of biosurfactants, their interaction with soil and contaminants and scale up and cost for biosurfactant production.     

Effect of surfactants on peroxidase activity. III. Effect of nonionic surfactants

The effect of a series of nonionic surfactants on the initial rate of the peroxide oxidation of 5-aminosalicylic acid in solution catalyzed by horseradish peroxidase was studied. As the surfactant concentration increases, the peroxidation rate first increases, then decreases, and the increase/decrease cycle is repeated. The primary increase may be induced by a change in properties of the medium under the action of surfactants, and the following decrease, by the enzyme inhibition. The secondary increase may be explained by to a change in the enzyme conformation and an increase in the accessibility of its active site for the substrate due to the immobilization of the protein in the surfactant aggregates, whereas the secondary decrease, by a shielding of the protein with these aggregates. For communication II, see [1].     

Development of synthetic lung surfactants

We have previously reported the development of a reconstituted lung surfactant consisting of an organic solvent extract of natural bovine lung surfactant supplemented with synthetic lipids. This "artificial" surfactant was used successfully to treat surfactant deficiency states both in animals and humans. We now report on the successful testing of a synthetic lung surfactant consisting of a lipid-bound protein isolated from natural lung surfactant and the lipids present in the "artificial" lung surfactant and now used in the same concentration but in a synthetic, commercially available form. The synthetic lung surfactant possessed the in vitro and in vivo surface properties characterizing the "artificial" lung surfactant. In order to identify the components of the synthetic lung surfactant that are responsible for the required surface properties, a series of 25 simple mixtures was prepared. Of these, three possessed surface properties very similar to those of the "artificial" lung surfactant and the synthetic lung surfactant, in vitro as well as in vivo. These three mixtures had four components in common. Besides dipalmitoyl phosphatidylcholine and the lipid-bound protein, they each had a saturated fatty acid, palmitic or stearic, and they each had an acidic phospholipid, phosphatidylglycerol or phosphatidylserine.     

Adjuvant activity of water-insoluble surfactants

A series of cationic amine and diamine surfactants, nonionic surfactants, and traditional vaccine adjuvants were compared for capacity to induce serum IgG antibody. With one exception, none of the aliphatic primary, secondary, tertiary or quaternary amines or diamines exhibited adjuvant activity beyond that of the dilute hexadecane emulsion vehicle nor was a structure-activity relationship determined. Avridine, a lipoidal diamine, potentiated the antibody response, but not the level of some nonionic surfactant adjuvants or Freund's adjuvants. Among the nonionic surfactants, T1501 tetronic block copolymer, trehalose dimycolate, sorbitan trioleate, and glycerol trioleate were equivalent (P greater than 0.05) to Freund's complete adjuvant in their capacity to stimulate antibody. The latter two surfactants have not been reported previously. The results suggest that certain nonionic surfactants in dilute oil-in-water emulsions are effective replacements for Freund's adjuvants. Such adjuvant emulsions are easily prepared, easily injected and do not produce the grossly adverse reaction observed with Freund-type water-in-oil emulsions.     

酶法合成表面活性剂

用生物技术来研制表面活性剂是当前国际生物工程领域中发展起来的一个新课题。本文概述了用酶法合成五种类型的表面活性剂,单酰化甘油酯类表面活性剂,糖酯类表面活性剂,氨基酸类表面活性剂,磷酯类表面活性剂及氨基酸糖类表面活性剂。     

Analysis of supercooling activities of surfactants

Supercooling-promoting activities (SCAs) of 25 kinds of surfactants including non-ionic, anionic, cationic and amphoteric types were examined in solutions (buffered Milli-Q water, BMQW) containing the ice nucleation bacterium (INB) Erwinia ananas, silver iodide (AgI) or BMQW alone, which unintentionally contained unidentified ice nucleators, by a droplet freezing assay. Most of the surfactants exhibited SCA in solutions containing AgI but not in solutions containing the INB E. ananas or BMQW alone. SCAs of many surfactants in solutions containing AgI were very high compared with those of previously reported supercooling-promoting substances. Cationic surfactants, hexadecyltrimethylammonium bromide (C16TAB) and hexadecyltrimethylammonium chloride (C16TAC), at concentrations of 0.01% (w/v) exhibited SCA of 11.8 °C, which is the highest SCA so far reported. These surfactants also showed high SCAs at very low concentrations in solutions containing AgI. C16TAB exhibited SCA of 5.7 °C at a concentration of 0.0005% (w/v).     

Control of membrane-attached biofilms using surfactants

The effect of surfactants on membrane-attached biofilms (MABs) was studied in a lab-scale extractive membrane bioreactor (EMB). Twenty-two surfactants were screened for their potential of increasing the cell wall negative charge (i.e. the electrostatic repulsion between bacteria) of Burkholderia sp. JS150 bacterial strain. Surfactants resulting in increased bacterial negative charge were further investigated for their effects on MAB population morphology and MAB attachment behaviour. Microscopic investigation of the bacterial population in MABs showed that surfactants affect the development of flagella, suggesting changes in the attachment capability of the JS150 strain in the presence of different surfactants. Among the screened surfactants, teepol showed the best characteristics in relation to the reduction of MAB accumulation, and it was tested in an EMB system for the extraction of monochlorobenzene from a synthetic wastewater. Comparison with a control EMB, operated without surfactants under the same conditions, proved that teepol effectively reduces MAB accumulation on the membrane walls. As a result, the overall mass transfer coefficient in the presence of teepol was 53% higher than in the control EMB.     

碱性脂肪酶与表面活性剂相互作用的研究

研究洗涤剂中常见的非离子表面活性剂、阴离子表面活性剂和阳离子表面活性剂对由扩展静霉（Ｐｅｎｉｃｉｌｌｉｕｍ ｅｘｐａｎｓｕｍ）产生碱性脂肪酶活性的影响及该酶在各种常见的洗涤剂溶液中的稳定性。     

Effect of surfactants on cellulose hydrolysis

The effect of surfactants on the heterogeneous enzymatic hydrolysis of Sigmacell 100 cellulose and of steam-exploded wood was studied. Certain biosurfactants (sophorolipid, rhamnolipid, bacitracin) and Tween 80 increased the rate of hydrolysis of Sigmacell 100, as measured by the amount of reducing sugar produced, by as much as seven times. The hydrolysis of steam-exploded wood was increased by 67% in the presence of sophorolipid. At the same time, sophorolipid was found to decrease the amount of enzyme adsorbed onto the cellulose at equilibrium. Sophorolipid had the greatest effect on cellulose hydrolysis when it was present from the beginning of the experiment and when the enzyme/cellulose ratio was low. (c) 1993 John Wiley & Sons, Inc.     

Biophysical inhibition of synthetic lung surfactants

The biophysical activity and inhibition of a series of synthetic surfactant mixtures was studied and correlated with physiological effectiveness in restoring pressure-volume (P-V) mechanics of excised lungs. Results showed that several simple mixtures of dipalmitoyl phosphatidylcholine (DPPC) with fatty acids or diacylglycerols could be formulated to give good adsorption facility and dynamic surface tension lowering to less than 1 mN/m in pulsating bubble measurements at 37 degrees C. However, although biophysical activity approached that of natural lung surfactant (LS) and a related surfactant extract (CLSE) under normal conditions, surface properties were sharply inhibited by relatively small amounts of the plasma protein albumin (2 mg/ml) with minimum surface tensions greater than 30 nM/m even at high surfactant concentrations (5-20 mg lipids/ml). This sensitivity to biophysical inhibition was markedly increased compared to LS and CLSE, and had direct consequences for physiological efficacy: in spite of initially high activity, synthetic surfactants did not exert beneficial effects on P-V mechanics when instilled into surfactant-deficient excised rat lungs. Endogenous protein material was shown to be present upon surfactant recovery by lavage, and bubble measurements confirmed surface activity well below pre-instillation levels. Moreover, full biophysical activity was restored when lavage fluid was extracted to separate the synthetic surfactants from endogenous inhibitors. These results show that it is important to define relative sensitivity to biophysical inhibition in the development of effective lung surfactant substitutes. In addition, the existence of inhibition effects can generate an apparent lack of correspondence between initial biophysical activity and ultimate physiological actions of exogenous surfactant mixtures.     

Towards commercial production of microbial surfactants

Biosurfactants or microbial surfactants are surface-active biomolecules that are produced by a variety of microorganisms. Biosurfactants have gained importance in the fields of enhanced oil recovery, environmental bioremediation, food processing and pharmaceuticals owing to their unique properties--higher biodegradability, lower toxicity, and effectiveness at extremes of temperature, pH and salinity. However, large-scale production of these molecules has not been realized because of low yields in production processes and high recovery and purification costs. This article describes some practical approaches that have been adopted to make the biosurfactant production process economically attractive: these include the use of cheaper raw materials, optimized and efficient bioprocesses and overproducing mutant and recombinant strains for obtaining maximum productivity. The application of these strategies in biosurfactant production processes, particularly those using hyper-producing recombinant strains in the optimally controlled environment of a bioreactor, might lead towards the successful commercial production of these valuable and versatile biomolecules in near future.     

Synthesis of positively charged galactose-bearing surfactants

An approach to the synthesis of cationic carbohydrate surfactants with potential antimicrobial and transfecting activities is proposed.     

Bacterial destruction of anionic sulfoethoxylate surfactants

A Pseudomonas putida strain G was isolated and its activity in the destruction of sulfoethoxylates (surfactants) was studied as a function of the cultivation conditions. Ultrastructural changes were found in the cells utilizing sulfoethoxylates. Sulfoethoxylates were found to be decomposed by P. putida G via two pathways: (a) desulfation of the molecule and (b) cleavage of the alkyl ester bond. The intermediate products were not toxic and did not pollute the habitat. The strain can be used for microbiological purification of sewage.     

Enzymatic synthesis of arginine-based cationic surfactants

A novel enzymatic approach for the synthesis of arginine N-alkyl amide and ester derivatives is reported. Papain deposited onto solid support materials was used as catalyst for the amide and ester bond formation between Z-Arg-OMe and various long-chain alkyl amines and alcohols (H2N-Cn2, HO-Cn; n = 8-16) in organic media. Changes in enzymatic activity and product yield were studied for the following variables: organic solvent, aqueous buffer content, support for the enzyme deposition, presence of additives, enzyme loading, substrate concentration, and reaction temperature. The best yields (81-89%) of arginine N-alkyl amide derivatives were obtained at 25 degrees C in acetonitrile with an aqueous buffer content ranging from 0 to 1% (v/v) depending on the substrate concentration. The synthesis of arginine alkyl ester derivatives was carried out in solvent-free systems at 50 or 65 degrees C depending on the fatty alcohol chain length. In this case, product yields ranging from 86 to 89% were obtained with a molar ratio Z-Arg-OMe/fatty alcohol of 0.01. Papain deposited onto polyamide gave, in all cases, both the highest enzymatic activities and yields. Under the best reaction conditions the syntheses were scaled up to the production of 2 g of final product. The overall yields, which include reaction, Nalpha-benzyloxycarbonyl group (Z) deprotection and purification, varied from 53 to 77% of pure (99.9% by HPLC) product.     

Potential commercial applications of microbial surfactants

Surfactants are surface-active compounds capable of reducing surface and interfacial tension at the interfaces between liquids, solids and gases, thereby allowing them to mix or disperse readily as emulsions in water or other liquids. The enormous market demand for surfactants is currently met by numerous synthetic, mainly petroleum-based, chemical surfactants. These compounds are usually toxic to the environment and non-biodegradable. They may bio-accumulate and their production, processes and by-products can be environmentally hazardous. Tightening environmental regulations and increasing awareness for the need to protect the ecosystem have effectively resulted in an increasing interest in biosurfactants as possible alternatives to chemical surfactants. Biosurfactants are amphiphilic compounds of microbial origin with considerable potential in commercial applications within various industries. They have advantages over their chemical counterparts in biodegradability and effectiveness at extreme temperature or pH and in having lower toxicity. Biosurfactants are beginning to acquire a status as potential performance-effective molecules in various fields. At present biosurfactants are mainly used in studies on enhanced oil recovery and hydrocarbon bioremediation. The solubilization and emulsification of toxic chemicals by biosurfactants have also been reported. Biosurfactants also have potential applications in agriculture, cosmetics, pharmaceuticals, detergents, personal care products, food processing, textile manufacturing, laundry supplies, metal treatment and processing, pulp and paper processing and paint industries. Their uses and potential commercial applications in these fields are reviewed. Received: 29 July 1999 / Received revision: 8 November 1999 / Accepted: 9 November 1999     

表面活性剂对林可霉素发酵生产的影响

在林可霉素发酵过程中,当向培养基中加入表面活性剂十二烷基磺酸钠(SDS)、吐温80(Tween 80)和曲拉通(Triton X-100)时,林可霉素的产量受到较大影响。本研究应用响应面设计法(Response surface design)对表面活性剂的配比进行了优化,得到的优化配比为:十二烷基磺酸钠为31.13 mg/100 mL,吐温80为51.97 mg/100 mL,曲拉通为16.9 mg/100 mL。将该优化配比应用于林可霉素发酵,产量提高了36.67%。