Erwinia herbicola CHS1065 produces antifungal compounds highly related to herbicolin A. In 11 Tn5 mutants that have lost the antifungal activity, the transposon insertion is located on a 170-kb plasmid present in CHS1065. This plasmid was designated pHER1065. When analyzing these antifungal mutants, it was found that the genes for the biosynthesis of the antifungal compounds were organized in at least two clusters on pHER1065. Upon insertion of the aphII gene of Tn5 and genes for plasmid mobilization in pHER1065, the plasmid could be stably introduced into Escherichia coli. All the E. coli exconjugants expressed an antifungal activity that was quantitatively and qualitatively comparable to the activity produced by E. herbicola CHS1065. Amino acid analysis and molecular weight determinations of the antifungal compound produced by CHS1065 were identical to those of herbicolin A.

We inserted kanamycin resistance (Km) gene and mobilized function (Mob) gene on the plasmid of E. herbicola CSH1065 by using DNA molecular cloning and genetic recombination techniques. Therefore, the plasmid of E. herbicola CSH1065 to E. coli HB101 could be transferred by conjugation. The expression of those genes concerning fungi inhibition function (Fib) of E. herbicola CSH1065 in E. coli HB101 was observed. This result confirmed again the fungi inhibition genes of E. herbicola CSH1065 is only related to its plasmid genome not to its chromosome genome. Meanwhile those yellow pigment genes located on the plasmid don't involve the antifungi function of E. herbicola CSH1065. All those results were convinced by DNA molecular hybridizations.

AbstractA search for micro‐organisms associated in high numbers with roots or leaves of corn, grapevine, chicory, soybean, sunflower, barley and sugarbeet yielded a collection of over 10 000 bacterial strains. Within this collection, antifungal strains have been selected, using direct or indirect in‐vitro assays against one target fungus per crop. The target fungi were selected based on their agronomic relevance as pests.Isolates with antifungal activity were tested for their spectrum of activity against a set of phytopathogenic fungi. In 15 bacterial strains with broad‐spectrum activity, belonging to the species Erwinia herbicola. Serratia plymuthica, Pseudomonas fluorescens, P. aureofaciens, P. cepacia and Bacillus subtilis, the active compounds have been identified. Bacterial strains belonging to the same taxon, but isolated from different ecological niches and/or different places in Europe, produce identical compounds. In two bacterial taxa (Erwinia and Serratia) this was reflected in a genetic conservation of the regions coding for antifungal activity. In both cases, the biosynthetic pathways proved to be genetically complex.All of the compounds identified in this study have been described previously in bacterial strains isolated from analogous or completely different ecosystems.

Antifungal rhizobacteria were obtained from maize, barley and chicory using direct or indirect isolation procedures. Effective isolates were tested for broad‐spectrum activity against a set of phytopathogenic fungi. Isolates with broad‐spectrum activity were identified as Pseudomonas fluorescens, P. cepacia, Serratia liquefaciens, S. plymuthica and Bacillus sp. Broad‐spectrum compounds produced by P. cepacia and Erwinia herbicola were characterized as pyrrolnitrin and herbicolin‐like compounds respectively.