Promising substitute of inconsistent algal alginates: exploring the biocompatible properties of di-O-acetylated, poly-L-guluronate-deficient alginate from soil bacterium Pseudomonas aeruginosa CMG1418.

Abstract

The structural inconsistencies in commercial algal alginates have limited their reliability and quality for various applications. Therefore, the biosynthesis of structurally consistent alginates is crucial to replace the algal alginates. Thus, this study aimed to investigate the structural and alginate's structural and functional properties of Pseudomonas aeruginosa CMG1418 as a substitute. To achieve this, the CMG1418 alginates were physiochemically characterized using various techniques such as transmission electron microscopy, Fourier-transform infrared ¹H-NMR, ¹³C-NMR, and gel permeation chromatography. The synthesized CMG1418 alginate was then subjected to standard tests to evaluate its biocompatibility, emulsification, hydrophilic, flocculation, gelling, and rheological properties. The analytical studies revealed that CMG1418 alginate is an extracellular and polydisperse polymer with a molecular weight range of 20 000-250 000 Da. It comprises 76% poly-(1-4)-β-D-mannuronic acid (M-blocks), no poly-α-L-guluronate (G-blocks), 12% alternating sequences of β-D-mannuronic acid and α-L-guluronic acid (poly-MG/GM-blocks), 12% MGM-blocks, 172 degrees of polymerization, and di-O-acetylation of M-residues. Interestingly, CMG1418 alginate did not show any cytotoxic or antimetabolic activity. Moreover, compared to algal alginates, CMG1418 alginate exhibited higher and more stable flocculation efficiencies (70-90%) and viscosities (4500-4760 cP) over a wide range of pH and temperatures. Additionally, it displayed soft to flexible gelling abilities and higher water-holding capacities (375%). It also showed thermodynamically more stable emulsifying activities (99-100%) that surpassed the algal alginates and commercial emulsifying agents. However, only divalent and multivalent cations could slightly increase viscosity, gelling, and flocculation. In conclusion, this study explored a structurally di-O-acetylated and poly-G-blocks-deficient, biocompatible alginate, and its pH and thermostable functional properties. This research suggests that CMG1418 alginate is a superior and more reliable substitute for algal alginates in various applications, such as viscosifying, soft gelling, flocculating, emulsifying, and water-holding.