**4. Biosynthesis**

Several excellent research articles [22, 31] have analysed recent progress in bacterial alginates biosynthesis. The oxidation of a carbon source to acetyl-CoA, which enters the TCA cycle and is converted to fructose-6-phosphate through gluconeogenesis, is the first step in alginate biosynthesis. Fructose-6-phosphate is then transformed to GDP-mannuronic acid, which is a precursor to alginate synthesis, through a sequence of biosynthetic transformations. The biosynthetic process can be divided into four stages in general: (a) synthesis of the GDP-mannuronic acid precursor; (b) cytoplasmic membrane transfer and polymerisation of polymannuronic acid; (c) periplasmic transfer and modification; and (d) export through the outer membrane. Polymannuronic acid is acetylated at the O−2 and/or O−3 positions by multiple transacetylases at stage (c), resulting in post-polymerisation modification of alginates [35, 36]. A family of epimerase enzymes then performs epimerization to transform certain non-acetylated M residues to G residues [37–40]. Finally, transmembrane porin sallow alginate to exit the cell [25].

Alginate is generally available in sodium, potassium, or calcium forms in the market. Both alginate salts are widely used as biopolymers in medical, biomedical, medicinal, and cosmeceutical applications [1, 41–43]. In the presence of divalent and trivalent metal cations in the aqueous setting, sodium alginate can form ionotropic hydro-gelled matrices [44, 45]. Alginate is a biopolymeric excipient widely used in pharmaceutical and biomedical products such as capsules, hydrogels, gels, managed release systems, beads, bio-adhesives, pellets, patches, microparticles, and nanoparticles as an emulsifying agent, disintegrant, thickener, coating content, stabiliser, and so on [46–49]. Based on the cross-linkers used and cross-linking techniques used, alginates can entrap drug molecules and release them in a rate-controlled pattern. It's used in managed drug release systems and targeted drug delivery systems to ensure that drugs have the best bioavailability at their target sites [12]. Sodium alginate, calcium alginate, and alginate derivatives have also been used in the manufacture of wound dressings. Water absorption power, swelling and gelling capabilities, ability to be crosslinked, controllable porosity, biodegradability, and biocompatibility nonimmunogenic, haemostatic nature, bioactivity (support the proliferation process), bio-similarity to extracellular matrices, bio-adhesivity, ability to encapsulate drugs and control of drug releasing, cost-effective, etc. are all important properties that make these biopolymeric materials ideal for wound dressing formulations. Alginate has the ability to absorb up to 20 times its weight in body fluids and liquids, creating a hydrophilic gel. Alginate's excellent gelling properties made it suitable for wound dressing applications [12, 50].
