Abstract
Poly-γ-glutamic acid (γ-PGA) is a biodegradable biopolymer produced by several bacteria, including Bacillus subtilis and other Bacillus species; it has good biocompatibility, is non-toxic, and has various potential biological applications in the food, pharmaceutical, cosmetic, and other industries. In this review, we have described the mechanisms of γ-PGA synthesis and gene regulation, its role in fermentation, and the phylogenetic relationships among various pgsBCAE, a biosynthesis gene cluster of γ-PGA, and pgdS, a degradation gene of γ-PGA. We also discuss potential applications of γ-PGA and highlight the established genetic recombinant bacterial strains that produce high levels of γ-PGA, which can be useful for large-scale γ-PGA production.
Highlights
Poly-γ-glutamic acid (γ-PGA) is a natural anionic biopolymer without a fixed molecular weight comprised of only glutamic acid residues [1]
In addition to its several advantageous properties, γ-PGA is mainly produced by non-harmful bacteria, and can be safely used in industrial applications. γ-PGA fermentation or production can be achieved using different strains, substrates, and bioreactors through various processes
Comparing high-yield γ-PGA strains reported in various studies under the same growth conditions can help identify the strains that are the most efficient fermentation starters
Summary
Poly-γ-glutamic acid (γ-PGA) is a natural anionic biopolymer without a fixed molecular weight comprised of only glutamic acid residues [1]. Γ-PGA is produced by bacteria, especially Bacillus species. Deletion of pgsB, pgsC, or pgsA, which are located in the same operon (Figure 2), blocks γ-PGA synthesis in baTcatbelreia1l. The pgdS gene did not broadly exist in the Bacillus strains but was found in B. amyloliquefaciens, B. atrophaeus, B. axarquiensis, B. gibsonii, B. licheniformis, B. malacitensis, B. mojavensis, B. nakamurai, B. paralicheniformis, B. subtilis subsp. The fact that B. anthracis and other species do not harbor pgsE (Figure 8) may explain the fact that it does not secrete γ-PGA, which is instead anchored to the cell membrane. The results of the phylogenetic diversity revealed that the conservation of genes decreased in the following order: pgsC > pgdS > pgsE > pgsA > pgsB (Figures 3–7). Γ-PGA production is increased in recombinant strains, the culture medium must be supplemented with antibiotics to maintain the enhanced or disrupted genes, which increases the cost of fermentation
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