Abstract
Polyglutamic acid (PGA) is water-soluble and biodegradable polymer with high production cost. For feasible PGA production, feather hydrolysate (FH) was used as fermentation substrate. 30L fermentation of native feather was realized to obtain keratinase enzyme using Streptomyces pactum DSM 40530. Fermentation broth was concentrated by cross-flow filtration where the enzyme activity increased by 8.75-fold and 8×103UL-1d-1 of enzyme activity was the optimum for achieving 75% degradation per gram of feather. 40g/L of FH was used with different media compositions to produce PGA using Bacillus licheniformis 9945a. Among four different cultivation where L-glutamate, tri-sodium citrate and glycerol were used as the constituents of Medium E, highest yields of γ-PGA and cell dry matter (CDM) were obtained from cultivation-1, at 5.4±0.4 and 8.6±0.5g/L, respectively, despite the culture media did not contain glutamic acid. In cultivation-2, which was not only missing glutamate but also citrate, the γ-PGA and CDM yielded 3.2±0.2 and 7.8±0.4g/L, respectively whereas it was only 1.9±0.2 and 4.2+0.4g/L when FH was used as the sole substrate in cultivation-3. When cultivation-4 was adopted where only glycerol was missing, the γ-PGA and CDM yields slightly increased to 2.3±0.2 and 5.5±0.3g/L, respectively. This is the first study that achieved the production of γ-PGA from FH.
Highlights
Polyglutamic acid (PGA) is a biodegradable, protease-resistant, non-immunogenic and unusual anionic homopolyamide that is made of D- and Lglutamic acid units with nylon-like properties upon esterification of its carboxyl side chains
It can either be in the form of only L-glutamic acid residues or D-glutamic acid residues. γ-PGA is a ribosome-independent synthesized protein since glutamate is polymerized inside the cell via the γ-amide linkages which results in eliminating the inhibiting effect of substances like chloramphenicol during protein translation. γ-PGA can be in the watersoluble free acid or salt form with a variety of cations such as Na+, Mg2+, K+, NH4+ or Ca2+ where the latter is completely soluble (Ashiuchi et al 2006, Ogunleye et al 2015)
Despite the recalcitrance structure of keratin, it can be degraded efficiently by certain bacteria by means of their keratinolytic proteases or keratinases. While established methods such as steam pressure cooking requires high-energy input and the resulted feather meal is deficient in methionine and histidine which restricts to be used as animal feed, hydrolysis of keratinous waste by keratinolytic activity represents an attractive method for its bioconversion and improved nutritional value (Kornillowicz-Kowalska & Bohacz 2011)
Summary
Polyglutamic acid (PGA) is a biodegradable, protease-resistant, non-immunogenic and unusual anionic homopolyamide that is made of D- and Lglutamic acid units with nylon-like properties upon esterification of its carboxyl side chains. Γ-PGA has been produced extensively using especially Bacillus species It can either be in the form of only L-glutamic acid residues or D-glutamic acid residues. Despite the recalcitrance structure of keratin, it can be degraded efficiently by certain bacteria by means of their keratinolytic proteases or keratinases. While established methods such as steam pressure cooking requires high-energy input and the resulted feather meal is deficient in methionine and histidine which restricts to be used as animal feed, hydrolysis of keratinous waste by keratinolytic activity represents an attractive method for its bioconversion and improved nutritional value (Kornillowicz-Kowalska & Bohacz 2011)
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