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Review
. 2021 Oct;44(10):2003-2034.
doi: 10.1007/s00449-021-02597-5. Epub 2021 Jun 16.

Fungal biosurfactants, from nature to biotechnological product: bioprospection, production and potential applications

André Felipe da Silva  1   2 , Ibrahim M Banat  3 , Admir José Giachini  1 , Diogo Robl  4
Affiliations
Review

Fungal biosurfactants, from nature to biotechnological product: bioprospection, production and potential applications

André Felipe da Silva et al. Bioprocess Biosyst Eng. 2021 Oct.

Abstract

Biosurfactants are in demand by the global market as natural commodities that can be added to commercial products or use in environmental applications. These biomolecules reduce the surface/interfacial tension between fluid phases and exhibit superior stability to chemical surfactants under different physico-chemical conditions. Biotechnological production of biosurfactants is still emerging. Fungi are promising producers of these molecules with unique chemical structures, such as sophorolipids, mannosylerythritol lipids, cellobiose lipids, xylolipids, polyol lipids and hydrophobins. In this review, we aimed to contextualize concepts related to fungal biosurfactant production and its application in industry and the environment. Concepts related to the thermodynamic and physico-chemical properties of biosurfactants are presented, which allows detailed analysis of their structural and application. Promising niches for isolating biosurfactant-producing fungi are presented, as well as screening methodologies are discussed. Finally, strategies related to process parameters and variables, simultaneous production, process optimization through statistical and genetic tools, downstream processing and some aspects of commercial products formulations are presented.

Keywords: Bioprocess; Biosurfactants; Downstream; Filamentous fungi; Screening; Yeasts.

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Conflict of interest statement

The authors declare no financial or commercial conflict of interest.

Figures

Fig. 1
Fig. 1
Biosurfactants are amphiphilic molecules, their composition consists of hydrophilic (carboxylic acids, alcohols, amino acids, phosphates, peptides, mono-, di- or polysaccharide cations or anions) and hydrophobic (hydrocarbon chains or saturated/unsaturated fatty acids) moieties (a). These molecules accumulate at phase interfaces of different polarities and stabilise heterogeneous phases (oil/air bubble droplets). b Thus, adsorption reduces the free energy per unit area needed to create a new surface, a reduction that is closely related to surface tension (liquid–air) and interfacial tension (liquid–liquid) [note the displacement of surface oil over water in c] [34]. Biosurfactant monomers (d) due to their self-assembly properties on reaching the Critical Micellar Concentration (CMC) (e), can form aggregated micellar structures (f) [35]. Micelle formation and solubility occur just above the Krafft temperature (g), i.e., the critical temperature at which micellar self-assembly occurs due to dissolution of the hydrated surfactant crystals (h) [36]. Bioemulsifiers are less effective in reducing surface tension and are involved in the formation and stabilization of emulsions between two immiscible phases (i) [31, 32]
Fig. 2
Fig. 2
Chemical structure of fungal glycolipids and polyol lipids (adapted from [12] and [39]). The hydrophilic portions are highlighted in blue
Fig. 3
Fig. 3
Collapse drop test occurs with the addition of oil and samples (3:1 v/v) to the wells of the microplate. First, oil is added to form a hydrophobic surface. Afterwards, drops of samples containing biosurfactants will collapse on contact with this surface as shown in a, and Parafilm-M test in b, where rn=1,2,3,4 = drop radius and n analyzed sample
Fig. 4
Fig. 4
The oil spread test occurs with the addition of water and a smaller volume of oil to form a thin hydrophobic layer. Then, the test sample is added over the oil layer and provides the displacement of the area on the oil surface
Fig. 5
Fig. 5
EI24 test: addition of equal volumes (1:1) of hydrophobic substrates and samples containing biosurfactants in graduated tubes. Subsequently, the mixture is stirred at high speed, being maintained in the absence of disturbance for phase separation and stability of the formed emulsion (a). The emulsification percentage value can be measured according to (b)
Fig. 6
Fig. 6
The microbial adhesion to hydrocarbon test is initiated by washing fungal cells to remove contaminants, followed by a resuspension in buffer solution (PUM) until reaching a standardized optical density (DO). Thereafter, the hydrocarbon is added, and the mixture is stirred. After complete separation of phases, the organic phase is removed, and the optical density is measured again (a). The percentage value of microbial cell adhesion to hydrocarbons is obtained as in (b)
Fig. 7
Fig. 7
Methylene blue-CTAB agar test (a) and blood hemolysis test (b). Biosurfactant-producing strains produce a halo when grown in a solid medium of defined composition. The cultivation period for obtaining the results varies according to culture strain
Fig. 8
Fig. 8
Microplate assay is initiated by placing a grid paper under a microplate. The culture medium/water in a microplate well is considered to have a flat surface. A sample with biosurfactant will have a change at the well edge and the fluid surface will become concave, and consequently distorts the image (a). The penetration test occurs by adding a hydrophobic paste to the wells of the microplate, which is covered with mineral oil. Then, the sample is stained with red solution and added to the hydrophobic surface. The presence of biosurfactants is detected through its influence on the rupture of the barrier (interface) of the oil layer in the paste, which favors the entry of silica into the hydrophilic phase, and the upper phase changes the color from light red to cloudy white (b)
Fig. 9
Fig. 9
The double diffusion agar test occurs with the addition of biosurfactant samples in wells in a row regularly spaced against another row of wells filled with a known cationic or anionic element. The appearance of precipitation lines (48 h) between the wells indicates the ionic character of the biosurfactants
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