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Glycolipids

From Biosynthesis to Biological Activity toward Therapeutic Application Maria H. Ribeiro, Eva Fahr, and Sara Lopes

Research Institute for Medicines (iMed.ULisboa), Department of Pharmaceutical Sciences and Medicines, Faculty of Pharmacy, Universidade Lisboa, Lisbon, Portugal
*Corresponding author: mhribeiro@ff.ulisboa.pt

1.1 Introduction

Biosurfactants are surface active biomolecules, mostly produced by microorganisms, with a wide range of industrial applications. Biosurfactants are usually designed with a hydrophilic moiety composed of amino acids or peptides, anions, or cations; mono-, di-, or polysaccharides; and a hydrophobic moiety consisting of unsaturated, saturated, or fatty acids (Banat et al. 2010).

Since biosurfactants are a wide group of biocompounds, there are different methods of classification. The most usual is classification according to the nature, chemical composition and microbial origin of the biosurfactants. They can be divided into five major categories: glycolipids, fatty acid/phospholipid, lipopeptide/lipoprotein, polymeric and surfactant particles (Cortés-Sánchez et al. 2013).

Among the biosurfactants, glycolipids have been intensively studied and are one of the most promising categories for commercial production and utilization (Warnecke and Heinz 2010). Glycolipids with one or two sugar residues attached to different lipid backbones can be found in cell membranes of bacteria, fungi, plants and animals in the form of sterylglycosides, glycosylceramides, and diacylglycerolglycosides (Warnecke and Heinz 2010). The most well-known glycolipids are sophorolipids (Bogaert et al. 2007; Oliveira et al. 2015), mannosylerythritol lipids (Im et al. 2001), rhamnolipids and trehalose lipids (Figure 1.1). The glycolipods that this chapter will focus on is a case study of trehalose lipids, also known as trehalolipids.

Figure 1.1 The chemical structures of the most common glycolipids.

The amphiphilic character triggers them to aggregate at liquid interfaces with different degrees of polarity and hydrogen bridges, giving them the ability to reduce surface- and interfacial-tension between solids, liquids and gases.

Furthermore most biosurfactants exhibit characteristics such as tolerance to pH, temperature and ionic strength, biodegradability, low toxicity, detergency, emulsification, de-emulsification and foaming. There is considerable interest in potential applications, due to their environmental friendly character and sustainability (Geys et al. 2014; Makkar et al. 2011; Santos et al. 2016; Smyth et al. 2010). Nowadays the preservation of the Earth as a sustainable planet is one of humanities greatest concerns. In line with this concern about the environment, many industries are changing to a global viewpoint on the future of manufacturing. In fact, they have recognized the potential of living cells in the pre-treatment of raw materials, processing operations, product modifications, selective waste management, energy recycling and conservation.

Biosurfactants are quite adaptable, their performance is versatile in a wide range of applications, in different areas, such as pharmaceutics, cosmetics, agronomy, food, beverages, metallurgy, agrochemicals, organic chemicals, petrochemicals, fertilizers, and others (Abdel-Mawgoud and Stephanopoulos 2018). The main applications in the pharmaceutical field are as anti-microbial, anti-cancer, anti-viral and anti-adhesive agents, immunological adjuvants, and in drug and gene delivery (Abdel-Mawgoud and Stephanopoulos 2018).

1.1.1 Application of Biosurfactants

The most commonly used surfactants are chemically produced from petroleum, these synthetic derived agents are generally toxic and not biodegradable. This problem motivates the search for more environmentally friendly surfactants, such as biosurfactants produced by microorganisms, which provides a wide range of applications (Santos et al. 2016; Vijayakumar and Saravanan 2015).

Biosurfactants have several advantages over petroleum based surfactants, such as structural diversity, low toxicity, greater biodegradability, the ability to function in wide ranges of pH, temperature and salinity, as well as greater selectivity, lower protein denaturing potency and lower critical micellar concentration (CMC). The wide range of industrial applications include the field of petroleum industry as well as bioremediation, agricultural, food processing, health, chemical, and cosmetic industries (Abdel-Mawgoud and Stephanopoulos 2018; Santos et al. 2016). The following sections present an overview of the most investigated application fields for biosurfactants.

1.1.1.1 Petroleum Industry

The major accruing market for biosurfactants is currently the petroleum industry, which offers different applications for them (Santos et al. 2016).

Petroleum, also known as crude oil is a natural energy source found beneath the earth´s surface. It is a resource that is in great demand, and has become the leading raw material for development and the economy in the past century. It basically consists of two to three phases (liquid/solid and gas), the industry uses several mechanisms to separate these (Almeida et al. 2016). Biosurfactants have shown promising applications in this industry, such as extraction, transportation or petrochemical manufacturing (Makkar et al. 2011).

Approximately 50-65% of oil residues are found in porous rocks, caused by high forces of capillarity, interfacial tension between the aqueous and the hydrocarbon phases and the high viscosity of the crude oil. These residues can often not be recovered by conventional oil recovery methods (Almeida et al. 2016; Santos et al. 2016). Biosurfactants can lower the interfacial tension between oil/rock and oil/water interfaces, in that way the oil-recovery can be enhanced. A mixture containing the producing microorganism can be injected into the porous rock, which will be sealed for a certain time to allow microbial growth. Therefore, the production of biosurfactants allows the breakdown of the oil film in the rocks and oil flow can be re-established. Experiments have shown that the use of indigenous microorganisms Arthobacter sp, Pseudomonas sp and Bacillus sp resulted in a reduction of paraffin from 29.8 to 25.5 % in 9 months (Bachmann et al. 2014).

Because of their amphipilic structure, biosurfactants have highly emulsifying properties which are important for the extraction of oil, to form stable water-oil emulsions (Bachmann et al. 2014).

1.1.1.2 Bioremediation

Oil spills during the transport, exploration or refining of petroleum products cause huge environmental hazards. The primary transportation method of oil products is via ship, which increases marine oil contamination due to the routine operations of ship washing, and accidents during exploration and transportation (Souza et al. 2014). Conventionally the spilled oil is removed via physicochemical methods, which doesn't solve the problem in the long term, since the contaminants are simply removed from one environment to another, which often results in the development of even more toxic byproducts. For this reason, the search for biological alternatives, such as biosurfactants, is important to contribute to environmental health (Silva et al. 2014).

Generally, bioremediation is a process where toxic compounds are fully or partially degraded through living organisms such as bacteria or plants.

The production of biosurfactants generally requires a hydrophobic and hydrophilic carbon source in the culture medium. This process is economically and environmentally friendly when using waste products as substrates (Silva et al. 2014). The biodegradation of the oil-derived compounds is based on different mechanisms. Through the production of biosurfactants the bioavailability of the hydrophobic substrate for the producing bacterium increases, whereby the surface tension of the medium around the bacteria reduces, which results in a lower interfacial tension. Another mechanism is a membrane modification through an interaction of the cell surface and the biosurfactant, which increases the hydrophobicity of the cell wall by reducing the lipopolysaccharide index through an adhesion of the hydrocarbons, without damaging the membrane. Through these mechanisms the formation of hydrogen bonds is blocked and the surface/interfacial tension is reduced, enhancing the dispersion of the hydrocarbon into micelles (which breaks down the biomass into drops) and amplifies the bioavailability and biodegradability (Aparna et al. 2011; Santos et al. 2016).

Regarding the environmental industry trehalose lipids are used as microbial-enhanced oil recovery, biodegradation of polycyclic aromatic hydrocarbons or oil-spill treatments, in the cosmetics industry and most importantly in the biomedical field with biologic properties, like anti-microbial, anti-viral (Azuma et al. 1987) and anti-tumor activities (Franzetti et al. 2010; Gudiña et al. 2013; Kadinov et al. 2020). Moreover, they can act as therapeutic agents due to their functions in cell membrane interactions (Franzetti et al. 2010).

1.1.1.3 Agriculture

Great agricultural damage can be caused by plant pathogens, which results in the use of chemical pesticides that have a number of negative effects on the health of humans and the environment. This is why the requirement and search for natural and environmental friendly pesticides is highly relevant. Biosurfactants, show anti-microbial properties against a...