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Poly-y-glutamic acid (y-PGA) is a biodegradable biopolymer which can be used in the medicine, food and cosmetics industries as well as in agriculture. Animal manure and waste from glutamic acid production are mass-produced solid organic waste and have high potential to pollute water environments if not properly disposed. These wastes contain high amount of carbohydrate, protein and other nutrients, and therefore can be used as substrate for producing y-PGA bio-organic fertilizer that is fermented by y-PGA producing bacteria.The strain C1, which was isolated and screened from soil samples, was confirmed to be able to produce high amount ofγ-PGA. The purified y-PGA from the metabolic products of C1, was made up of glutamic alone characterized by amino acid analysis, while its absorption peak was 210 nm determined by ultraviolet absorption spectrum analysis. The volumetric yield of y-PGA reached 18.3 g·L-1 at 37℃in the fermentation medium. The strain C1 was identified as a Bacillus subtilis by morphological, physiological and biochemistry experiments and 16S rDNA gene sequence analysis. The optimal growth conditions for strain C1 were: 37℃, pH 6.5,20 mL to 30 mL of medium volume per 150 mL Erlenmeyer flask and 20 h of incubation.. The optimal carbon, organic nitrogen and inorganic nitrogen source for the growth of C1 were sucrose, yeast extract and ammonium sulfate, respectively.Results from hydroponic experiments showed that there had no significant effects on the biomass, height and accumulation of N, P and K of maize seedlings, when bacterium y-PGA was added in the whole-strength nutrient solution. In contrast, remarkablely increase of above- and under-ground biomass, height and accumulation of N, P and K of the maize seedlings were obtained under the half- and the quarter-strength nutrient solution. All y-PGA treatments increased the values of relative chlorophyll content (SPAD), furthermore, the pronounced enhancement were found when bacterium y-PGA was added in either the half- or the quarter-strength nutrient solution. The biomass and SPAD value were increased with the increase of y-PGA level until the y-PGA level was 0.30 g·L-1, while the root activity maintained higher values in all y-PGA treatments than in the control without y-PGA and was not related to the amount ofγ-PGA added.The results from pot experiments showed that the biomass and height of maize seedlings, length and width of leaf, and stem thickness were significantly increased by application of theγ-PGA bio-organic fertilizer (C1OF). The dry weights of shoots and roots in the C1OF treatment were 2.53 and 2.13 times more than those in the treatment with chemical fertilizer (CF), while increased by 24.75% and 38.17% more than those in the treatment with non-C1-fermented organic fertilizer (OF). The accumulation of N, P and K in maize seedlings also was significantly increased by application of C1OF. The N accumulation in shoot and root of maize seedlings were increased by 16.92% and 27.81% compared to the application of CF, while increased by 65.51% and 85.08% compared to the OF treatment. The P and K accumulation had the same trend as N accumulation. Besides, the contents of soluble protein and sugar, the SOD and root activity, and both soil microbial biomass C and N were all increased in the C1OF treatment.In conclusion, Bacillus subtilis C1 showed highγ-PGA productivity, andγ-PGA and theγ-PGA bio-organic fertilizer had significant growth-promotion effects on maize seedlings. Thus, the strain C1 and the C1 fermented organic fertilizer had a great potential in solid waste utilization in agriculture.
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