Abstract
Bacillus sp. SW1-2 producing poly glutamic acid (PGA), locally isolated from Eastern province in Saudi Arabia, was characterized and identified based on 16S rRNA gene sequencing. Phylogenetic analysis revealed its closeness to Bacillus megaterium. The homopolymer consists mainly of glutamic as indicated in the analysis of amino acid. Preliminary optimization of PGA production, through a series of one-variable-at-a-time (OVAT) experiments, revealed maximum PGA production of 10.5 (g/L). Statistically based experiments were applied to optimize culture conditions for production of PGA. Effect of 15 variables were examined for their significance on PGA production using Plackett-Burman factorial design. Among those variables; Na-citrate, (NH4)2SO4, glutamic acid and CaCl2.2H2O were most significant variables that encouraged PGA production, while those negatively affected were; glycerol, glucose and phosphate buffer. Significant parameters were further investigated using Box-Behnken design to define the optimal medium composition. Based on statistical analysis, maximal PGA production on optimized medium was 36.5 (g/L) which was more than 4-folds the basal production medium. Verification experiment was carried out to examine model validation and revealed more than 95% validity. Key words: Poly glutamic acid, Bacillus megaterium, statistical experimental design, optimization, one-variable-at-a-time (OVAT).
Highlights
(γ-glutamic acid) (γ-poly glutamic acid (PGA)) is a homopolymer of Dand L-glutamic acid units naturally produced by severalBacillus species as an extracellular polymer (Cheng et al, 1989; Kunioka and Goto, 1994; Young and Gross, 1997; Ashiuchi and Misono, 2002; Oppermann-Sanio and Steinbüchel, 2002; Yong et al, 2011)
Purified strains were tested for PGA production by cultivation on basal production medium supplemented with glutamic acid or ammonium sulfate as nitrogen source
Data on PGA production were subjected to multiple linear regressions using Microsoft Excel 97 to estimate t-value, P-value and confidence level
Summary
(γ-glutamic acid) (γ-PGA) is a homopolymer of Dand L-glutamic acid units naturally produced by several. Bacillus species as an extracellular polymer (Cheng et al, 1989; Kunioka and Goto, 1994; Young and Gross, 1997; Ashiuchi and Misono, 2002; Oppermann-Sanio and Steinbüchel, 2002; Yong et al, 2011). It is biodegradable, edible, and non-toxic to human and the environment. Series of OVAT experiments were carried out to determine critical variables level affecting PGA production. Special emphasis was given to the impact of significant variables interactions on biopolymer production applying BoxBehnken design
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