Earthworm polysaccharide and its antibacterial function on plant-pathogen microbes in vitro

The experiment was conducted to study earthworm (Eisenia fetida) polysaccharides and their antibacterial function on plant-pathogen microbes in vitro. The following results were obtained. (1) Polysaccharides isolated from common earthworms and induced earthworms had broad-spectrum antibacterial activities on plant-pathogen microbes in vitro. (2) Antibacterial activities of earthworm polysaccharides were assayed by the Disk method. The diameter of bacteriostasis circle to Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Pseudomonas solanacearum Smith, Sclerotinia sclerotiorum, Colletotrichum lagenarium, Fusarum oxysporum, Phytophthora boehmeriae Sawada, Rhizoctonia solani Kühn and Botrytis cinerea was 2.10 ± 0.08, 2.33 ± 0.05, 3.30 ± 0.08, 4.28 ± 0.10, 4.15 ± 0.06, 1.53 ± 0.05, 2.15 ± 0.06, 4.58 ± 0.10, 2.40 ± 0.08, and 2.48 ± 0.10 cm, respectively. (3) Antibacterial function of mucopolysaccharide for Pseudomonas aeruginosa and Staphylococcus aureus increased significantly (P < 0.05) after earthworms were induced by Escherichia coli, while minimum inhibitory concentrations (MIC) did not change for Escherichia coli. (4) The antibacterial component of polysaccharides isolated from both earthworms and induced earthworms were composed of five molecules by HPLC-MS. The composition at retention time 5.3 min was Glu-Xyl-Glu-Xyl, with a molecular weight of 533 Da, while that at 6.0 min was 452 Da, which was composed of Glu-Rha-Rha or Rha-Glu-Rha. The molecular weight of the 6.7 min composition was 678 Da, which was composed of Glu-Glu-Glu-Xyl-Xyl.