has been an exclusive task for industrial organic chemistry. However, just as microorganisms have been used in industrial processes to afford enzymes, vaccines, antibiotics, wine, and beer, the production of surfactants can also be carried out in this way. Furthermore, the rapid and recent advance on bioprocesses envisions the feasibility of producing BS on a large scale. Research and technological developments have tried to look for cost competitiveness proposing cheaper raw materials and more affordable downstream processes. For example, it has been demonstrated that some agro‐industrial wastes such as molasses from sugar industry [10] or whey from dairy industry [11] can be useful. Other aspect on BS is the possibility to improve physicochemical properties or the productivity of microorganisms via biochemical or genetic engineering techniques.
BS have very attractive properties such as low toxicity and high biodegradability (degraded by other microorganisms); which is very well aligned to current needs imposed by international regulations. It now is considered that biocompatibility of a product is a parameter as important as its cost and performance, so the chemical industry is compelled to implement new strategies for manufacturing more sustainable materials without scarifying efficiency. The numerous advantages of versatile BS compared to synthetic surfactants explain the increasing attention on the topic from the early twenty‐first century (Figure 2.4). Although publishable activity on BS dates back 57 years, the boom has emerged for the last 20 years. Only in the last eight years, more than half of the known references on BS have been reported. BS are recognized for resisting a wide range of pH, salt concentration, and temperature [12] and have the ability to reduce surface tension in exactly the same way as chemical and oleochemical surfactants, so these can find the same application niches, i.e. as the key components of countless formulations for almost any sector of the contemporary industry [13]. Hence, BS are excellent candidates for different industrial applications like oil recovery, detergents, cleaning products, degreasers, fertilizers, agrochemicals, textile products, paints, mining, inter alia. Moreover, BS can attend applications where strong eco‐friendly features are demanded, e.g. bioremediation of soil and water due to hydrocarbon spills [14, 15], water treatment, food processing [16], health, sanitizers, cosmetics, and pharmaceuticals [17].
Figure 2.3 General chemical structures for four types of rhamnolipids: monorhamnose‐monolipid, monorhamnose‐dilipid, dirhamnose‐monolipid, and dirhamnose‐dilipid.
As it has been observed, classification for a surfactant molecule comprises all the chemical species that share a binary amphiphilic feature. The production of microbial surfactants involves a strong character of sustainability and circular economy. Its production seems to be the right choice that will revolutionize the way the chemical industry, applications, and markets work. Glycolipids such as SL and rhamnolipids appear to be the species with the greatest potential to be developed at larger scales in the coming years. In addition, there are some synergies with other chemical compounds that can enhance surface activities and performances, which makes ipso facto possible the introduction of BS in the market via innovative formulations.
Figure 2.4 Number of publications on biosurfactants from 1963 to April 2020.
Among all primary and secondary metabolites, BS play interesting roles for microbial life. Some authors suggest that their emulsifying properties help microorganisms to adapt to environments, enhancing nutrient availability in soil or water and allowing cell adherence for water‐insoluble substrate transport [18]. Since BS can inhibit microbial growth, those microorganisms producing BS can become predominant in their environment [19].
As mentioned above, BS are biodegradable and suitable for different industrial applications; for this reason, there is abundant research about their production and natural sources. Biosynthesis of BS are distributed among archaea, bacteria, yeasts, and molds, but depending on the group, genus, and species of microorganisms, BS structures become significantly different.
2.2 Biosynthesis of BS by Archaea and Bacteria
There are few papers related to Archaea as BS producers, compared to bacteria. Those who have been studied are alkaliphiles from the marine environment [20]. In contrast, bacteria produce mainly glycolipids, such as rhamnolipids, trehalolipids, and glucolipids; biosynthesis is restricted to actinobacteria, proteobacteria, cyanobacteria, and firmicutes (87%), other phyla represent between 1.0 and 2.5% of glycolipid‐producing bacteria [21]. On the other hand, lactic acid bacteria (LAB), produce BS showing important roles in LAB colonization due to antimicrobial activities against fungi and bacteria. LAB BS are constituted by polysaccharides, glycolipids, glycolipopeptides, and proteins [22, 23]. Figure 2.5 depicts the distribution of prokaryote‐producing BS. A broad review of scientific literature proved that prokaryotes are the predominant group of microorganisms related to BS production (Table 2.2), particularly bacteria.
Figure 2.5 Phyla of prokaryote producers of biosurfactants.
Source: Sharma et al. [22] and Satpute et al. [23].
Table 2.2 Archaea and bacteria as biosurfactant producers.
| Biosurfactant | Microorganism | Carbon source |
|---|---|---|
| Rhamnolipids | Pseudomonas aeruginosa | Oil residues, corn oil, waste frying oil [24–26] |
| Pseudomonas fluorescens | Hexadecane, olive oil [26] | |
| Pseudomonas luteola | Molasses [26] | |
| Pseudomonas chlororaphis | Glucose [26] | |
| Pseudomonas putida | Molasses, glucose [26] | |
| Pseudomonas stutzeri | Palm oil mill effluent [27] | |
| Pseudomonas pachastrellae | Barley pulp [28] | |
| Pseudomonas desmolyticum | Hexadecane [29] | |
| Burkholderia glumae | Canola oil [26] | |
| Burkholderia plantarii | Glucose [26] | |
