## 1 Introduction  
Biosurfactants (BSs) are surface-active molecules produced by microorganisms covering a wide range of chemical compounds including carbohydrates, lipids, peptides, and fatty acids. Biosurfactants show diversity in their structures but all of them can reduce interphase tension. Biosurfactants are surface-active substances produced by microorganisms. They possess unique properties such as low toxicity, biodegradability, and effectiveness at extreme temperatures, pH levels, and salinities. These compounds have diverse structures, including glycolipids, lipoproteins, and phospholipids, which contribute to their versatility. Biosurfactants reduce surface and interfacial tension, promoting emulsification and enhancing the bioavailability of hydrophobic compounds, making them valuable in environmental remediation, pharmaceuticals, and the food industry [1, 2]. Acid oil, derived from the refining processes of vegetable oils, is a valuable feedstock in MEL production due to its high fatty acid content. Its properties include good solubility and the availability of essential nutrients for microbial growth. The advantages of using acid oil in MEL production include its cost-effectiveness, as it is a byproduct of the oil refining industry, and its sustainability, reducing waste and promoting circular economy practices. Additionally, acid oil's composition enhances the yield and quality of MEL, making it an efficient choice for industrial applications. Environmentally, utilizing acid oil promotes waste valorization by converting a byproduct that might otherwise be discarded into valuable biosurfactants. This process not only minimizes waste but also reduces the environmental impact associated with disposal, contributing to a more sustainable and circular economy. These biomolecules comprise hydrophilic and hydrophobic moieties linked together. The most common hydrophobic moieties used for the production of biosurfactants are vegetable oils, fatty acids, waste frying oil, and oil refinery waste [3]. Waste oils from households, vegetable oil refineries, and the soap industry are suitable for microbial growth and bio-surfactant production [4]. Acid oil has been identified as an economic resource as it is readily available in large quantities at most vegetable oil refineries; about 1060 vegetable oil refineries in India process about 25 million tons of vegetable oils and generate about 4-4.2 million tons of acid oil at their sites, and these acid oils are considered as unwanted and are disposed of at 40-42,000 INR/ton. Manosylerithrytol lipid (MEL) is one of the glycolipid biosurfactants abundantly produced by several kinds of microorganisms [5; 6]. The biosynthesis of MEL includes \(\beta\) oxidation pathway intermediates and also a new type of chain-shortening pathway (partial \(\beta\) oxidation). This newly supposed pathway is also studied using enzyme inhibitors, and it has been found that it has a significant effect on MEL production [7]. The productivity of MEL varies with the nutritional environment of the growing microorganism and carbon substrate provided: either hydrophilic or hydrophobic. Moreover, the fatty acid composition of the hydrophobic part depends upon the characteristics of the producing microbial strain. The constitutional diversification of MEL executes remarkable changes in its physicochemical properties including the surface-active, self-assembling properties and versatile biochemical actions like anticancer and cellular differentiation [8; 9]. MEL has also been applied in various industrial products like cosmetic products for skin care and hair repair and has also been used as an antimicrobial agent [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33]. As per one study [34], _Pseudozyme antarctica_ is a top producer of mannosylerythitol lipids (MELs). In a study examining various _Pseudozyme species_ for MEL production from soybean oil, _P. fusiformata, P. parametarctica_, and _P. tsukubaensis_ were identified as new MEL producers. _P.