Sequential Optimization Approach for Enhanced Production of Poly(γ-Glutamic Acid) from Newly Isolated Bacillus subtilis

Ishwar B. Bajaj and Rekha S. Singhal*

Food Engineering and Technology Department, Institute of Chemical Technology, University of Mumbai, Matunga, IN-400019 Mumbai, India

Article history:

Received December 24, 2008
Accepted March 19, 2009

Key words:

poly(γ-glutamic acid), Bacillus subtilis, biopolymer, response surface methodology


A bacterial strain of marine origin showing production of poly(γ-glutamic acid) (PGA) has been identified by taxonomical and 16S rRNA studies as Bacillus subtilis. A sequential optimization approach was applied for improving the PGA production. The effect of carbon sources, nitrogen sources and pH on the production of PGA was investigated by one factor-at-a-time method. Plackett-Burman design was then adopted to select the most important nutrients influencing the yield of PGA. After identifying the most significant nutrients, response surface methodology (RSM) was used to develop a mathematical model to identify the optimum concentrations of the key nutrients for higher PGA production, and confirm its validity experimentally. PGA production was further improved by supporting the medium with α-ketoglutaric acid. The PGA production increased from 7.64 to 25.38 g/L by using the sequential optimization methods.


*Corresponding author: 
                                               ++91 22 24 145 616
                                               ++91 22 24 145 614

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