Production of a Specific Bacteriocin by Xanthomonas campestris pv. citri

Among phytopathogenic bacteria, some species such as Agrobacterium tumefaciens,1,2) Corynebacterium spp.,3) C. michiganense pv. michiganense,4) Pseudomonas spp.,5,6) Ps. solanacearum,7) Ps. syringae pv. syringae8) and Erwinia carotovora9,10) were reported to probuce bacteriocins. In most of these reports, bacteriocins were utilized for taxonomical purposes, namely, the plant pathogenic bacteria were grouped on the basis of the productivity of bacteriocins or susceptibility to them. In our previous papers11,12), we have reported two kinds of antibacterial subsances produced by Xanthomonas campestris pv. citri treated with chloroform vapor. Of these antibacterial substances, the one composed of a protein having molecular weight of ca. 300,00012) was found to be a kind of specific bacteriocin only produced by X. campestris pv. citri in this experiment. The isolates of xanthomonads shown in Table 1 were inoculated on the plate of YPDA medium (peptone 0.6g, dextrose 3g, yeast extract 3g, agar 15g, pH 7.2) at a distance of 2 to 3cm from one other and incubated at 30C for 48hr. The Petri dish thus prepared was placed upside down and the lid of it was poured with 1ml of chloroform to sterilize bacteria. The plate was then overlaid with 1ml of the suspension of indicator bacteria (conc.: ca. 107-8cells/ml) mixed with 5ml of 0.5% YPDA medium. The plate was incubated at 30C for 24hr. The productivity of antibacterial substance was detected by inhibition zone formed around colony. All of the 19 isolates of X. campestris pv. citri used in this experiment produced antibacterial substance active against several pathovars of X. campestris as shown in Table 2. The antibacterial substance produced clear inhibition zones on the lawns of X. campestris pv. campestris X1-1-1, X. campestris pv. oryzae H5809 and H5854, and X. campestris pv. cucurbitae X1-3-1. Very weak activity was observed on