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Table 2 Exemplar engineering of homologous and heterogeneous hosts

From: Microbial synthesis of poly-γ-glutamic acid: current progress, challenges, and future perspectives

Strains

Engineering methods

Fermentation medium

Production (g/L)

Ref.

B. licheniformis WX-02

Expression of glr gene encoding glutamate racemase

Glucose, l-glutamic acid, sodium citrate, NH4Cl, MgSO4, K2HPO4, CaCl2, ZnSO4, MnSO4

14.38

[75]

B. amyloliquefaciens LL3

Double-deletion of genes pgdS and cwlO

Sucrose, (NH4)2SO4, MgSO4, KH2PO4, K2HPO4

7.12

[84]

B. amyloliquefaciens LL3

Deletion of genes (rocR, rocG, gudB, odhA)

Sucrose, (NH4)2SO4, MgSO4, KH2PO4, K2HPO4,

5.68

[85]

B. subtilis ISW1214

Bearing the plasmid-borne PGA synthetic system

Sucrose, NaCl, MgSO4, KH2PO4, NaHPO4,xylose

9.0

[47]

E. coli BL21

Cloning and overexpressing γ-PGA biosynthesis genes

Glucose, yeast extract, l-glutamic acid, (NH4)2SO4

3.7

[76]

E. coli JM 109

Co-expressing γ-PGA synthetase and glutamate racemase

LB medium supplemented with l-glutamate or glucose

0.65

[48]

B. amyloliquefaciens

Deletions of genes (epsA-O, sac, lps, pta, pgdS, cwlO, luxS, and rocG gene, expression of synthetic small regulatory RNAs which repressed the rocG and glnA gene

Sucrose, (NH4)2SO4, MgSO4, KH2PO4, K2HPO4

20.3

[86]

B. subtilis PB5249

Knockout of genes (pgdS and ggt)

l-glutamic acid, citric acid, glucose, NH4Cl, K2HPO4, MgSO4·7H2O, FeCl3·6H2O, CaCl2·2H2O, MnSO4·H2O, pH 6.5

40

[87]

Bacillus licheniformis WX-02

Enhanced expression of pgdS gene

Glucose, sodium glutamate, sodium citrate, NH4Cl, MgSO4, K2HPO4, CaCl2, ZnSO4, MnSO4

20.16

[88]

Corynebacterium glutamicum

Cloning and expressing γ-PGA biosynthesis genes

Glucose, (NH4)2SO4, KH2PO4, MgSO4·7H2O, FeSO4·7H2O, MnSO4·4H2O, soy protein hydrolysate, thiamine hydrochloride, CaCO3

18

[54]

  1. Despite some progress, γ-PGA production remains low in these strains