Effect of Lead and γ-Polyglutamic Acid Produced from Bacillus subtilis on Growth of Brassica chinensis L.

γ-Polyglutamic acid (γ-PGA) has been reported to be an effective biosorbent for metal ions. In vitro binding of lead (II) (Pb) by γ-PGA produced from Bacillus subtilis NBRC16449 was examined and the effect of Pb and γ-PGA on Brassica chinensis L. grown in the laboratory was investigated. The results revealed that the optimal pH for Pb adsorption was 5.0. γ-PGA was stable at 35-50 °C and pH 5-7. The maximum removal efficiency was 87.9%. Brassica chinensis L. seeds were germinated and grown at 28±1 oC on filter paper soaked with Pb solution at 0, 50, 100 and 250 μM and γ-PGA at 0, 100, 500 and 1,000 mg/L for 7 days. The results indicated that Pb markedly inhibited growth of roots by reducing root length (P<0.05). However; the addition of 500 mg/L γ-PGA significantly protected seedlings from the adverse effects of Pb (P<0.05). Thus, γ-PGA has high potential as a biopolymer to be used for alleviation of Pb toxicities in plants.