Abstract
Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made from repeating units of l-glutamic acid, d-glutamic acid, or both. Since some bacteria are capable of vigorous γ-PGA biosynthesis from renewable biomass, γ-PGA is considered a promising bio-based chemical and is already widely used in the food, medical, and wastewater industries due to its biodegradable, non-toxic, and non-immunogenic properties. In this review, we consider the properties, biosynthetic pathway, production strategies, and applications of γ-PGA. Microbial biosynthesis of γ-PGA and the molecular mechanisms regulating production are covered in particular detail. Genetic engineering and optimization of the growth medium, process control, and downstream processing have proved to be effective strategies for lowering the cost of production, as well as manipulating the molecular mass and conformational/enantiomeric properties that facilitate screening of competitive γ-PGA producers. Finally, future prospects of microbial γ-PGA production are discussed in light of recent progress, challenges, and trends in this field.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0537-7) contains supplementary material, which is available to authorized users.
Highlights
Poly-γ-glutamic acid (γ-PGA) is an unusual anionic homopolyamide made from d-and l-glutamic acid units connected through amide linkages between α-amino and γ-carboxylic acid groups [1] (Additional file 1: Fig. S1)
Based on the glutamate residues present, poly-γ-glutamic acid (γ-PGA) may be classified as γ-l-PGA, γ-dPGA, and γ-LD-PGA
Another similar study was carried out using Corynebacterium glutamicum as the host, clone, and expression of the γ-PGA synthase genes pgsBCA from Bacillus subtilis TKPG011
Summary
Poly-γ-glutamic acid (γ-PGA) is an unusual anionic homopolyamide made from d-and l-glutamic acid units connected through amide linkages between α-amino and γ-carboxylic acid groups [1] (Additional file 1: Fig. S1). Most recent research on γ-PGA production is focused on optimizing growth conditions to increase yield, manipulate enantiomeric composition, and alter the molecular mass. The cost of production (including both productivity and substrates) is a major limitation for microbial γ-PGA production To this end, most research on γ-PGA fermentation has focused on optimizing growth conditions to improve γ-PGA yield, alter the enantiomeric composition, and manipulate the molecular mass of γ-PGA [25]. The engineered strain could produce γ-PGA from both glucose and l-glutamate, and co-expression of the racE gene further increased the production of γ-PGA to 0.65 g/L Another similar study was carried out using Corynebacterium glutamicum as the host, clone, and expression of the γ-PGA synthase genes pgsBCA from Bacillus subtilis TKPG011. Cane molasses may provide an even higher γ-GPA yield following optimization of the strain and fermentation process
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