Odeniyi Olubusola A, Avoseh David S
University of Ibadan, Nigeria.
Polim Med. 2018 Jul-Dec;48(2):91-97. doi: 10.17219/pim/105555.
Poly-γ‑glutamic acid (γ‑PGA) provides an environmentally friendly alternative to plastic materials which have widely polluted the environment.
The microbial production of γ‑PGA, an amino acid biopolymer with glutamic acid subunits, was investigated using renewable agricultural residues in an attempt to find cheaper substitutes for conventional synthetic media components.
Bacteria which produce γ‑PGA were isolated through depolymerizing Coix lacryma-jobi, a cellulosic grass, and the effects of various carbon and nitrogen sources, temperature, inoculant load, incubation period, and pH on γ‑PGA yield were determined after submerged fermentation. Bacterial growth was measured turbidimetrically at 550 nm. The γ‑PGA produced was characterized using Fourier transform infrared (FT-IR) spectroscopy and the polymer shape was determined using scanning electron microscopy (SEM).
The best γ‑PGA producer was molecularly identified as Bacillus toyonensis As8. The conditions which produced the highest γ‑PGA yield were glucose, ammonium sulfate, 25°C, a pH of 5.5, and an incubation period of 48 h. This bacterium yielded the most γ‑PGA (26.45 g/L) on cassava peels, while other agro-wastes (corn cob, sorghum leaves, Coix noir leaves, and rice bran) also supported bacterial growth with lower γ‑PGA yields than conventional carbon sources. The wrinkled γ‑PGA had absorbance peaks of hydroxyl, amide, carbonyl, and amine groups comparable with the ranges of those found in commercial γ‑PGA.
The use of agricultural by-products as fermentation substrates increased γ‑PGA yield and may therefore be used as substitute components in γ‑PGA production.
聚-γ-谷氨酸（γ-PGA）为广泛污染环境的塑料材料提供了一种环保替代品。
研究利用可再生农业残留物微生物生产γ-PGA（一种具有谷氨酸亚基的氨基酸生物聚合物），试图找到比传统合成培养基成分更便宜的替代品。
通过解聚纤维素草本植物薏苡分离出产生γ-PGA的细菌，在深层发酵后测定各种碳源、氮源、温度、接种量、培养时间和pH对γ-PGA产量的影响。通过在550nm处进行比浊法测量细菌生长情况。使用傅里叶变换红外光谱（FT-IR）对产生的γ-PGA进行表征，并使用扫描电子显微镜（SEM）确定聚合物形状。
产γ-PGA能力最强的菌株经分子鉴定为东洋芽孢杆菌As8。产生最高γ-PGA产量的条件为葡萄糖、硫酸铵、25°C、pH值5.5和培养时间48小时。该细菌在木薯皮上产生的γ-PGA最多（26.45g/L），而其他农业废弃物（玉米芯、高粱叶、黑薏苡仁叶和米糠）也支持细菌生长，但γ-PGA产量低于传统碳源。皱缩的γ-PGA的羟基、酰胺、羰基和胺基的吸收峰与市售γ-PGA中的吸收峰范围相当。
使用农业副产品作为发酵底物可提高γ-PGA产量，因此可作为γ-PGA生产中的替代成分。
