Abstract: A total of twelve endophytic actinomycetes and thirty-one endophytic bacteria were isolated from the surface-sterilized Ammodendron bifolium (Pall.) Jakovl roots, and the anti-microbial activity of the endophytic actinomycetes was screened, taking Escherichia coli, Staphylococcus aureus, and Bacillus subtilis as the indicator strains. Three of the 12 isolated endophytic actinomycetes could inhibit the growth of the three indicators, and two did not
show any anti-bacterial activity. The antagonism of the endophytic actinomycetes against the endophytic bacteria isolated from same plane was significant different. About 44.9% pairing showed inhibiting activity, with the diameters of inhibition zone from 8.25 mm to 28.5 mm, and the main targets were gram negative and bacillus bacteria, while 55.1% pairing did not show exhibiting activity, indicating that the interactions between endophytic actinomycetes and bacteria were quite diversified.

Key words: endophytic actinomycetes, anti-microbial activity, endophytic bacteria, Ammodendron bifolium, carbon and nitrogen stable isotopes, Coreius, interspecies diet relationship, Yibin reach.