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Table 3 Application of different strategies for improving γ-PGA production

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

Starting sources

Fermentation strategies

Main results

Ref.

B. licheniformis NCIM 2324

Optimization via one factor at a time

γ-PGA production increased from 5.27 to 26.12 g/L

[89]

B. subtilis CGMCC 0833

Applying pH-shift control strategy

Glutamate utilization increased from 24.3 to 29.5 g/L; γ-PGA production increased from 22.2 to 27.7 g/L

[62]

B. subtilis NX-2

Using a two-stage strategy for agitation speed control

The concentration of γ-PGA reached 40.5 g/L with increases of 17.7 %

[90]

B. subtilis NX-2

Adding different oxygen vectors

The concentration of γ-PGA reached 39.4 g/L with increase of 25.1 %

[59]

B. subtilis BL53

Adding some precursors

The production of γ-PGA increased to 25.2 g/L

[91]

B. subtilis C10

Addition of organic acid

The concentration of γ-PGA increased from 17.3 to 27.7 g/L

[92]

B. licheniformis NCIM 2324

Addition of metabolic precursors

The concentration of γ-PGA reached 35.75 from 26.12 g/L

[81]

B. licheniformis TISTR 1010

Using different feeding strategies

The γ-PGA concentration reached 27.5 g/L with increase of fivefold

[83]

B. subtilis NX-2

Using co-fermentation strategy

The production and productivity of γ-PGA reached 73.0 g/L and 0.81 g/L/h, respectively

[50]

B. subtilis CCTCC M 2012347

Solid-state fermentation

Using soybean residue and cane molasses to produce 103.5 g/kg of γ-PGA at 24 h under non-sterilized condition

[93]

B. amyloliquefaciens C1

Solid-state fermentation

Producing 0.0437 g γ-PGA per gram of substrates at 48 h

[94]

B. subtilis GXA-28

Addition of KCl

The γ-PGA yield increased from 18.36 to 25.62 g/L by 39.5 %

[95]

B. licheniformis

Heat stress and alkaline stress treatment

The maximum γ-PGA yield reached 29.34 g/L, 185 % higher than the control

[78]

B. licheniformis WX-02

Alkaline pH stress treatment

The maximum γ-PGA yield reached 36.26 g/L in the 50 L bioreactor, increased by 79 % compared with the control

[96]

B. subtilis NX-2

Adding hydrogen peroxide

The maximum concentration of 33.9 g/L γ-PGA was obtained by adding 100 µM H2O2 to the medium after 24 h. This concentration was 20.6 % higher than that of the control

[97]