Mesenterocin 52, a bacteriocin produced by Leuconostoc mesenteroides ssp. mesenteroides FR 52

F. MATHIEU, I.S. SUWANDHI, N. REKHIF, J.B. MILLIERE AND G. LEFEBVRE. 1993. One hundred and sixty-five isolates of Leuconostoc spp. were tested for bacteriocin production. Only one strain, Leuc. mesenteroides ssp. mesenteroides FR 52, isolated from a raw milk, produced a bacteriocin which was named Mesenterocin 52. This bacteriocin inhibited other Leuconostoc strains and several strains of Enterococcus and Listeria spp. No activity was found against lactococci and lactobacilli. The antibacterial spectrum differed from that of previously described Leuconostoc bacteriocins. Mesenterocin 52 was secreted into the medium during the growth phase. It was inactivated with protease treatments. At pH 7.0 it had a relative stability after heating at 100C (15 min), but it had a greater stability at pH 4.5 than at pH 7.0 after 6 h at 80C. The apparent molecular mass was estimated to be less than 10 kDa by ultrafiltration. Mesenterocin 52 showed a bactericidal effect on Leuconostoc paramesenteroides DSM 20288.     

Effect of Ammonium Ions on Egg Hatching and Second-Stage Juveniles of Meloidogyne incognita in Axenic Tomato Root Culture

Eggs, either dispersed or in masses, and second-stage juveniles (J2) of Meloidogyne incognita were exposed to different concentrations of ammonium ions in a nutrient agar medium upon which excised tomato roots were growing. Egg hatch and J2 penetration of the roots was slowed or inhibited at high (54 and 324 mg/liter) but not at low (1.5 and 9 mg/liter) concentrations of ammonium nitrate. The effect of ammonium on J2 appeared to be temporary and reversible. High potassium nitrate concentration (1,116 mg/liter) did not modify egg hatch or J2 penetration. There was no adverse effect from the high ammonium nitrate concentrations or an equivalent potassium nitrate concentration on root dry weight. Ammonium ions influence nematodes both directly and via plant roots and do so independently of microbial organisms.     

Properties of two bacteriocins synthesized byLeuconostoc strains

Mesenterocin 52 (Mes-52), was produced byLeuconostoc mesenteroides ssp.mesenteroides strain FR52 and dextranicin 24 (Dex-24) byLeuconostoc mesenteroides ssp.dextranicum strain J24. Dex-24 had a very narrow spectrum of antibacterial activity: it inhibited only some other strains ofLeuconostoc, contrary to Mes-52, which antagonized alsoListeria andEnterococcus sp. Mes-52 was partially purified by ammonium sulfate precipitation, gel filtration, cation exchange, and hydrophobic interaction chromatography. Mes-52 was biosynthesized and excreted into the medium during growth phase. At different temperatures media, there was an inverse relationship between the final bacteriocin-specific productivity and the mean growth rate. After novobiocin treatment, different mutants of strain FR 52 were obtained: nonproducing-sensitive (Bac^–Imm^–) and nonproducingimmune (Bac^–Imm⁺) strains. Many changes in the plasmid profiles of several mutants were detected by electrophoresis.     

Detection and properties of curvaticin 13, a bacteriocin-like substance produced byLactobacillus curvatus SB13

Lactobacillus curvatus SB13 biosynthetized during growth and excreted into the culture medium an inhibitor active againstListeria monocytogenes, Staphylococcus aureus, and some other Gram-positive bacteria. The native activity was linked to a non-dialyzable proteinaceous complex, destroyed by proteases, with an apparent molecular weight greater that 10 kDa. It showed a hydrophobic character, being soluble in alcohols and not denaturated by several organic solvents. The molecule was partially purified by ammonium sulfate precipitation and hydrophobic interaction chromatography.     

Purification of antibiotics produced byLentinus squarrosulus and preliminary characterization of a compound active againstRigidoporus lignosus

Purification and study of the antibiotic substances produced byLentinus squarrosulus have been carried out. The substances, excreted in the culture medium, were extracted withn-butanol. The butanolic extract inhibited growth ofRigidopurus lignosus, the agent of white rot ofHevea brasiliensis, and also ofMucor ramannianus, Rhodotorula mucilaginosa, Saccharomyces cerevisiae, andBacillus subtilis. The antibiotic fractions were purified by silicic acid column chromatography, then by reversed-phase (C18) high performance liquid chromatography (HPLC) followed by preparative adsorption thin-layer chromatography on silica gel. Two purified compounds were obtained: Ls1, which was active againstB. subtilis, and Ls2, which in addition was also active againstR. lignosus, M. ramannianus, and yeasts. Only the Ls2 compound is analyzed in this work. It was characterized by chemical reactions, ultraviolet spectroscopy, infrared spectroscopy, and proton nuclear magnetic resonance spectroscopy, which indicated the hydrophilic character of the molecule and the presence of alcoholic functions as well as a glycosidic moiety. The properties differed from those of already known antibiotics produced by different species ofLentinus.