Characterization of Bacillus subtilis RB14, coproducer of peptide antibiotics iturin A and surfactin.

Concerns about potentially harmful effects of long-term treatment of chemical insecticides and pesticides and the emergence of pathogens resistance to these agents make the use of natural bacterial antagonists specific to the pathogens-i.e.biological control of plant diseases-attractive to protect the environment.Bacillus subtilis, a Gram-positive, spore-forming bacterium, has proven safe over many years, because it is a non-pathogenic bacterium (3) and is even consumed in large quantities as the Japanese food natto (5).In recent years, there has been considerable interest in using B, subtilis as a biocontrol agent because of its ability to antagonize and repress plant diseases (13,14,16).We have also isolated several B. subtilis strains from suppressive composts, and shown that the bacteria were actually effective against plant pathogens (10-12).Whereas no correlation was usually observed between the size of the inhibition zone in vitro and the protective effect in glasshouse trials (16), we have observed a positive correlation between the strength of inhibition in vitro and the one of suppressiveness in vivo in our screening system (10,11).Isolating another bacterium with much stronger suppressiveness will be stimulating and beneficial for the biological control of plant deseases.A newly isolated bacterium B. subtilis RB 14 inhibited the growth of Fusarium oxysporum more significantly than any other bacteria isolated.In this paper, we describe the characterization of the bacterium RB 14 which produces lipopeptides, surfactin and iturin A.Suppressive effects in vitro on various phytopathogenic microorganisms by B. subtilis RB 14 were tested as shown in Table 1.Ten phytopathogenic fungi were grown on potato-dextrose agar (PDA) medium (potato-dextrose agar 39 g, distilled