Isolation and characterization of an antimicrobial endophytic bacterium ME-2 from mulberry twig in China

An antimicrobial endophytic bacterium strain, ME-2, was isolated from fresh mulberry twig tissues, and was identified. In addition, antimicrobial activities of the isolated strain were evaluated against Bacillus thuringiensis, Escherichia coli, Staphylococcus aureus,Beauveria bassiana and Mycoid bacillus using the antagonism test method. The results showed that, strain ME-2 was gram-positive, aerobic, motile, nitrate-reduction-positive, spore-formation-positive, methyl-red-negative, 0.6-0.7 × 1.5-1.6 μm long and rods. The strain could utilize D-glucose, D-lactose, sucrose, starch, citrate, gelatin and casein, and it was slightly halophilic with growth occurring at 10% (w/v) NaCl. According to the morphological, biochemical and physiological properties and sequence analysis of 16S rRNA gene, the strain was identified as Bacillus subtili (GeneBank accession No. JQ900623). Moreover, the results also showed that strain ME-2 exhibited strong antimicrobial activities against B. thuringiensis (76.0%), E. coli (69.8%), S. aureus(45.8%), B. bassiana (64.2%) and M. bacillus (86.3%). It was concluded that, strain ME-2 and its antimicrobial materials might be considered as a potential antimicrobial agents in the food and pharmaceutical industries.   Key words: Antimicrobial endophytic bacterium, identification, biochemical and physiological properties, 16S rRNA gene, antimicrobial activity.