PGA can be produced only through the microbial route, unlike alpha poly glutamic acid, which can be chemically synthesized. Among PGA producers, a broad classification was established in the form of glutamic acid-dependent PGA producers and glutamic acid — independent PGA producers, depending on the manda­tory requirement or nonrequirement for glutamic acid as a major component in the nutrient medium. Examples of glutamic acid-dependent producers of PGA include B. subtilis IFO 3335, B. subtilis NX-2, and Bacillus licheniformis ATCC 9945A and examples of glutamic acid-independent PGA producers include B. subtilis TAM-4 and B. licheni — formis SAB-26. Initial studies for the production of PGA was carried out using the strain B. licheniformis ATCC 9945A. The production medium formulated for PGA production contains a relatively high concentration (20—1230 mM) of Mn+2 and the more it was, the amount of D-glutamic acid present as well (Leonard et al., 1958a, b). Bacillus subtilis IFO 3335 was originally isolated from natto, a traditional fermented food in Japan, which has mucilage containing PGA and a levan. PGA produc­tivity of this strain was higher than that of B. licheniformis ATCC 9945A. Bacillus subtilis IFO 3335 could produce PGA at levels of 9.6 g/l, with an optimized medium with major components including 30 g/l of L-glutamic acid, 20 g/l of citrate, and 5 g/l ammonium sulfate. It was found that L-glutamic acid merely stimulated the production of PGA, which could initiate PGA produc­tions at lower concentrations (0.1 g/l), without the addi­tion of 30 g/l of L-glutamic acid (Kunioka and Goto, 1994; Kunioka, 1995). Cheng et al. (1989) isolated B. lichenifor­mis A35 while looking for amino acid producer under denitrifying conditions. A strain with extremely high production rates of PGA was isolated from fermented bean curd (Shi et al., 2006). The strain was found to be B. subtilis ZJU7. In an optimized culture medium contain­ing 60 g/l sucrose, 60 g/l tryptone and 80 g/l L-glutamic acid and after cultivated at 37 °C for 24 h, the yield of g-PGA reached 54.4 g/l. In an interesting study, a cocul­ture of C. glutamicum S9114 along with B. subtilis ZJU7 was attempted to reduce the input costs of addition of L-glutamic acid into the medium, and it yielded 32.8 g/l of PGA after 24 h of fermentation (Shi et al., 2007).

Various studies regarding the fermentative production, downstream processing and characterization of PGA have been reported in the literature. The review by Bajaj and Singal (2011) provides updated information on fermentative production of PGA by various bacterial strains and effect of fermentation conditions and media component on production of PGA in submerged as well as solid state fermentation.

PGA can be extracted from the fermentation medium by two different methods. A crude method involves centrifuging cells followed by precipitation of PGA by methanol or ethanol (chilled) (Goto and Kunioka,

1992) . Subsequent purification steps, involving gel permeation chromatography followed by reprecipita­tion have to be used to get PGA in a pure form. Another method exploiting the specific interaction of Cu+2 ions with PGA, gives relatively purer PGA (Troy, 1973). Further, the purity of the polymer is checked through peptide hydrolysis, followed by thin layer chromatog­raphy, to assess the constituent amino acids. Large amounts of PGA are produced microbially by the Japanese company Meiji Seika Kaisha Ltd employing B. subtilis strain F-021.