Acetan and Acetan-Like Polysaccharides: Genetics, Biosynthesis, Structure, and Viscoelasticity

Abstract

Bacteria produce a variety of multifunctional polysaccharides, including structural, intracellular, and extracellular polysaccharides. They are attractive for the industrial sector due to their natural origin, sustainability, biodegradability, low toxicity, stability, unique viscoelastic properties, stable cost, and supply. When incorporated into different matrices, they may control emulsification, stabilization, crystallization, water release, and encapsulation. Acetan is an important extracellular water-soluble polysaccharide produced mainly by bacterial species of the genera Komagataeibacter and Acetobacter. Since its original description in Komagataeibacter xylinus, acetan-like polysaccharides have also been described in other species of acetic acid bacteria. Our knowledge on chemical composition of different acetan-like polysaccharides, their viscoelasticity, and the genetic basis for their production has expanded during the last years. Here, we review data on acetan biosynthesis, its molecular structure, genetic organization, and mechanical properties. In addition, we have performed an extended bioinformatic analysis on acetan-like polysaccharide genetic clusters in the genomes of Komagataeibacter and Acetobacter species. The analysis revealed for the first time a second acetan-like polysaccharide genetic cluster, that is widespread in both genera. All species of the Komagataeibacter possess at least one acetan genetic cluster, while it is present in only one third of the Acetobacter species surveyed.

Keywords: Acetobacter; Komagataeibacter; acetan; acetan genetic cluster; acetan structure; acetan synthesis; acetan viscoelasticity; acetan-like polysaccharide; acetan-like polysaccharide genetic cluster; applications of acetan; extracellular polysaccharide.

Figure 1

Growing of Komagataeibacter pomaceti T5K1^T in static culture for production of acetan-containing biofilm.

Figure 2

Schematic linkage between two repeat units (framed in blue) in acetan of Komagataeibacter xylinus.

Figure 3

Schematic presentation of acetan secretion. The acetan oligosaccharide repeat unit is transported across the cytoplasmic membrane, assembled in periplasm, and transported out of the cell. The figure was created with Biorender.com.

Figure 4

Biochemical steps in acetan repeat unit synthesis by Komagataeibacter xylinus. In each step, an addition of a specific activated monosaccharide (in gray) to a growing intermediate chain of acetan repeat unit is catalyzed by a specific enzyme (in yellow).

Figure 5

AceH phylogeny reconstruction showing the divergence of the two acetan loci in Komagataeibacter and Acetobacter as deduced by PhyML using an LG substitution table and 1000 bootstrap replicates. The archetypal K. xylinus acetan locus and the newly found locus branches are colored in red and blue, respectively. The strains where acetan locus lateral transfer events may have occurred are in green color. Open and closed node circles indicate bootstrap values above 50% and 90%, respectively. For each AceH, its gene locus tag is also given. The tree was drawn using Iroki [45].

Figure 6

Potential applications of acetan-like polysaccharides. The figure was created with Biorender.com.