## 1 Introduction  
Sugar fatty acid esters, the so-called sugar esters (SEs), are biodegradable, odorless, non-irritating and non-toxic surfactants with broad applications in the food [1, 2], cosmetic [3] and pharmaceutical [4] industries. Moreover, SEs have gained attention thanks to their anti-bacterial (e.g., against numerous pathogenic species of Gram-positive and Gram-negative bacteria) and antifungal activity [5], while they are also reported as insecticides and miticides [6]. SEs are synthesized from renewable resources, such as sugars and fatty acids (FAs). Different types of sugars (e.g., sucrose, fructose, glucose and lactose) can be used as acyl-acceptors to produce SEs by esterification with FAs or transesterification with FA esters used as acyl-donors [7; 8; 9]. Glucose (Glc), a cheap and broadly available carbohydrate, has only one primary hydroxyl group, which predetermines a highly regioselective synthesis of SEs called glucose fatty acid esters (GEs) [10; 11]. Concerning acyl-donors, polyunsaturated fatty acids (PUFAs) can be used for this purpose, as it is known that PUFAs or PUFA derivatives have interesting biological properties, including their role in protecting against cardiovascular diseases, as well as antimicrobial and anticancer activities [12; 13; 14]. GEs can be synthesized both chemically and enzymatically [15; 16]. Lately, the main efforts in the processing of GEs have been focused on enzymatic synthesis because this is an advantageous method, requiring less energy and reducing solvent toxicity [11; 17], with lipases being the most important enzymes used for this synthesis [18; 19]. Commercially available immobilized lipases, such as _Candida antarctica_ B lipase, are used to catalyze the acylation of glucose with various FAs [20; 21]. Different sources of PUFAs can be used as sources of acyl groups, in the form of either FAs or FA esters, for GE production. Whilst terrestrial plant oils have been used as a source of PUFAs [22; 23], alternative and non-food supply sources, such as microalgae [24; 25] and fungi [26] could be used, thanks to their ability to produce microbial lipids rich in PUFAs of medicinal and nutritional interest. The microbial lipids, the so-called single-cell oils (SCOs), are synthesized by oleaginous microorganisms that are capable of producing substantial amounts of lipid stored within their cells [27; 28]. The genus of _Nammochloropsis_ includes various marine microalgae species, such as _N. salina_[29], _N. gaditana_[30; 31] and _N. oculata_[32], which are able to grow efficiently under a variety of culture conditions on low-quality waters, even on wastewaters, and accumulate lipids rich in PUFAs, such as eicosapentaenoic acid (EPA). Furthermore, oleaginous fungal species, such as _Cumtingham echinulata_ and _Umbelopsis isabellina_ are able to synthesize PUFAs, especially \(\gamma\)-linolenic acid (GLA) [13; 25], and are thus regarded as promising candidates for SCO production [33; 34; 35]. In a previous paper [36], we produced FA amides (FAAs) using lipids containing PUFAs as acyl group donors in different percentages and we concluded that FAAs can be used as bioactive compounds in various biological applications depending on their FA composition. The aim of the current paper was to enzymatically synthesize GEs using SCOs as acyl group donors similar to those used in FAA, either in the form of free fatty acids (FFAs) or in the form of fatty acid methyl esters (FAMEs). The reaction was carried out under various conditions, using two immobilized lipases as catalysts. SCOs, produced from various sources as described in [PERSON] et al. [36], contained EPA, GLA or oleic acid in high percentages. The biological activity of the aforementioned GEs against important human pathogens, the larvae of _Aedes aegypti_ and the SKOV-3 cancer cell line was studied and compared with GEs synthesized using olive oil and an EPA concentrate (i.e., a fish oil derivative containing EPA in very high percentages) as acyl group donors.