Enhanced production of poly-γ-glutamic acid by a newly-isolated Bacillus subtilis

Abstract

Application of poly-gamma-glutamic acid (γ-PGA), an unusual macromolecular anionic polypeptide, is limited due to the high cost associated with its low productivity. Screening bacterial strains to find a more efficient producer is one approach to overcome this limitation. Strain MJ80 was isolated as a γ-PGA producer among 1,500 bacterial colonies obtained from soil samples. It was identified as Bacillus subtilis, based on the biochemical and morphological properties and 16S rDNA gene sequencing. It produced γ-PGA from both glutamic acid and soybean powder, identifying it as a facultative glutamic acid-metabolizing bacterium. After optimization of its culture conditions, B. subtilis MJ80 showed γ-PGA productivity of 75.5 and 68.7 g/l in 3 and 300 l jar fermenters for 3 days cultivation, respectively, the highest productivity reported to date, suggesting MJ80 to be a promising strain for γ-PGA production.

Effects of media components and agricultural by-products on γ-polyglutamic acid production by Bacillus toyonensis As8

“…There was an increase in γ-PGA production when 10% of the γ-PGA producer was cultivated under optimal culture conditions in a medium that now contained either cassava peel, fructose or Coix leaves with ammonium sulfate, at 25°C and a pH of 5.5, over 48 h to yield 26.45 g/L, 23.23 g/L and 16.87 g/L of γ-PGA, respectively. at 1639.38 cm −1 , carbonyl absorption at 1439.00 cm −1 and hydroxyl absorption at 3417.00 cm −1 -are in agreement with those of other authors 17,19,26 who independently reported a strong amide (N-H) absorption at ~1620-1655 cm −1 , a weaker carbonyl (C=O) absorption at ~1394-1454 cm −1 , a strong hydroxyl (OH) absorption at ~3400-3450 cm −1 , and a characteristically strong amine (C-N) absorption in the range of 1085-1165 cm −1 . Characterization of the γ-PGA produced…”

“…These findings may be attributed to the fact that simple sugars are more desirable for bacterial metabolism since less energy is required to incorporate them into the metabolism of a cell. However, Ju et al 19 obtained a higher γ-PGA yield with 30 g/L of starch in the fermentation medium and B. subtilis MJ80, yielding 48.3 g/L of γ-PGA. The findings that citric acid and starch supported bacterial growth may be attributed to the ease with which these compounds convert into glutamic acids, through the tricarboxylic acid cycle and finally into poly-γ-glutamate.…”

“…5A,B). Ju et al 19 reported the highest γ-PGA yield by a B. subtilis strain at the end of a 5-day incubation before a fall in yield and concluded that -for that strain -the longer the incubation time, the higher the production of γ-PGA. There was a progressive increase in optical density proportional to increasing incubation time.…”

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

“…For an exogenous glutamate-independent producer, yeast extract proved to be an excellent nitrogen source for bacterial cell growth and γ-PGA production, but the high cost is a barrier to commercial production [ 51 ]. Therefore, attempts have been made to reduce the dosage or replace it with other media supplements such as (NH 4 ) 2 SO 4 or NH 4 Cl [ 56 ] (Table 1 ). As well as carbon and nitrogen sources, inorganic salts can affect the production, productivity, and quality of γ-PGA.…”

Isolation, Identification and Evaluation of Egyptian Bacillus sp. Isolates for Producing Poly-γ-glutamic Acid

“…, respectively). This high production of PGA may be related to the consumption of glucose and NH 4 Cl 2 as carbon and nitrogen sources in this media that classified as one of the most efficient C and N 2 sources [41].…”