# Microbial Biopolymers: From Production to Environmental Applications--A Review
## 2 Microbial Polymers
### Alginate  
Alginate is majorly extracted from seaweed species, e.g., _Sargassum cristafolium_, _Laminaria digitata_, and _Ascophyllum nodosum_[13; 38; 39], and from some bacterial strains, e.g., _Pseudomonas_ spp. and _Azotobacter_ spp. Alginate is an unbranched water-soluble hydrocolloid that belongs to the polysaccharide category. Guluronic and mannuronic acid-repeating monomeric units are adjoined by glycosidic connections to form alginate. The arrangement and composition of monomers designate the overall characteristics of alginate [142]. Alginate could provide a cross-link (egg-box) structure through ionic interactions and trapping cations. This chelating structural arrangement provides alginate with the capability of quenching heavy metals from wastewater. Hydrogels can be formed from alginate with the addition of calcium ions, which are usually stimulated by the incorporation of acids such as acetic acid. The potential of alginate-based hydrogels and their usage in the removal of dyes and heavy metals have been extensively studied by numerous researchers [143; 144; 145; 146; 147; 148; 149; 150]. Furthermore, alginate is considered to remove toxic pollutants from wastewater [151; 152]. Also, after contaminant elimination, algal biorefinery is a sustainable approach to recovering biochemicals (carotenoids, acetic acid, lactic acid, and eugenol), bioenergy (biohydrogen, biomethane, bioethanol, and biogas), and biomaterials(biochar, films, coatings, and carbon fiber) from biomass [153; 154] from algal biomass. As for environmental applications, [PERSON] et al. [155] developed sodium alginate beads for wastewater treatment, which were pH-sensitive and had controllable swelling behavior, using a post-cross-linking approach. The smart polysaccharide was found to be efficient for Cu\({}^{2+}\), Ag\({}^{+}\), Fe\({}^{3+}\), and methylene blue with a maximum adsorption capacity of 54.9, 82.8, 135.5, and 572.7 mg/g, respectively. In another study, [PERSON] et al. [156] fabricated pH-stimuli-responsive alginate/chitosan microcapsules containing linseed oil for the active corrosion protection of carbon steel. Benzotriazole, used as a corrosion inhibitor, was added through a layer-by-layer approach. The use of such smart biopolymers, known for their instantaneous response to pH variations, led to an observed enhancement in the release of the corrosion inhibitor at pH levels below 5. In the study conducted by [PERSON] et al. [157], sodium alginate and polyvinyl alcohol were used to create thin, porous hydrogel films with tiny pores. Due to the stimuli-responsive properties of sodium alginate, these smart hydrogel films demonstrated an ability to regulate the dimensions of the pores in response to changes in pH, thereby enhancing their efficiency in the process of separation. From advanced drug delivery systems to adaptable separation membranes, smart biopolymers hold great promise in shaping the future of technology and science. As ongoing research delves deeper into their potential, we can anticipate even more ground-breaking developments that capitalize on their unique properties. There are some limitations involved in using alginate as a biomaterial, such as mechanical stability, broad ranges of pore size distribution, mechanical stability, and osmotic swelling when subjected to physiological conditions. Additionally, due to changing environmental conditions, it is susceptible to variability in the proportion of gluuronic to mannuronic acid residues and their molecular weight [63; 158]. [PERSON] et al. [63] found that under diazotrophic conditions, its yield can be increased, and its constant molecular weight can be controlled by utilizing a continuous culture approach.