## 1 Introduction  
Exopolysaccharides (EPSs) represent the most significant group of biopolymers found outside the microbial cell wall. EPS components are predominantly carbohydrates produced by bacteria, cyanobacteria, and fungi [1, 2, 3], which possess many valuable biological activities, such as antimicrobial, immunoregulatory, and antioxidant activities [4, 5]. In recent years, EPSs have been receiving greater attention from the pharmaceutical industry as immune-stimulators, antitumor agents, and blood cholesterol-lowering agents. Moreover, EPSs are used as biomaterials for drug delivery due to their ability to conjugate to hydrophobic molecules and drugs [6, 7]. EPSs also have outstanding applications in the food industry as natural thickeners, stabilizers, emulsifiers, and texturizers [3]. Moreover, EPSs play important role in producing food additives and functional food ingredients [8; 9]. Recently, there has been increasing interest in the exploitation of bacterial EPSs. Bioactive EPSs are well-studied in many strains belonging to the genus _Lactobacillus_, _Bacillus_, _Lactococcus_, and _Streptococcus_[3; 5; 10]. Among them, EPSs produced by _Bacillus_ species have been recognized as safe, cost-effective, and stable. EPS extracted from a sponge-associated _B. licheniformis_ reduced the biofilm development of pathogenic bacteria, such as _Escherichia coli_ and _Pseudomonas fluorescens_[11]. Endophytic _B. amyloliguefaciens_ derived from the medicinal plant _Ophiapogon japonicus_ is a producer of EPS that showed great antitumoral activity against gastric cancers [12]. Of note, members of the genus _Bacillus_ produce complex EPSs. Different types of EPS, such as glucan, \(\gamma\)-polyglutamic acid (\(\gamma\)-PGA), levan, and fructan are found in _B. subtilis_, but their productivities rely on a substrate supplemented in the medium [13; 14]. _Bacillus subtilis_ EPS synthesized by a 15-gene operon _espA-O_ is found in the supernatant, which is rich in glucose and galactose [15]. EPS biosynthesis by the _eps_ gene cluster is a complex process, requiring genes responsible for the regulation, determination of chain length, synthesis, polymerization, and exportation of the repeating sugar units. While this EPS is produced by various sugar sources, levan is only synthesized when sucrose is supplied [3; 16]. Levan is classified as a homopolysaccharide that is mainly composed of \(\beta\)-(2\(\rightarrow\)6) fructan linkages with occasional \(\beta\)-(2\(\rightarrow\)1) branching, which is catalyzed by levansucrase in sucrose-rich environments [17; 18]. The levan produced by _B. licheniformis_ exhibited strong hypoglycemic and antioxidant activities, protecting the main organs in alloxan-induced diabetic rats [19]. _B. subtilis_ strains derived from honey were reported to produce levan that exhibited antiviral activity on avian influenza and type 40 adenovirus [20]. However, levan production capacity remains low and the production cost high due to the small amounts of levansucrase expressed in the wild-type strain. Thus, screening for _Bacillus_ species with high EPS production rates is required. One of the important therapeutic properties of EPSs is its antioxidant capacity. Excess of oxygen-derived hydroxyl radical, superoxide-free radical, and reactive oxygen species are the main factors contributing to various disorders including inflammation, lung injury, cancer, aging, and atherosclerosis [21; 22]. To prevent the generated oxidative stress, it is an urgent need to develop natural antioxidant agents for applications in the pharmaceutical and food industries, since synthetic antioxidants are suspected to be involved in carcinogenesis and liver damage. _L. reuteri_ and _L. vaginalis_ isolated from the gutecum of healthy poultry birds produced low EPS yields that showed potent in vitro antioxidant activity [4]. EPSs extracted from _Leuconostoc mesenteroides_ present during early kimchi fermentation displayed DPPH radical-scavenging activity, a lipid peroxidation inhibition effect, and a ferrous chelating ability.