Involvement of fengycin-type lipopeptides in the multifaceted biocontrol potential of Bacillus subtilis

in Applied Microbiology & Biotechnology (2005), 69(1), 29-38

In this work, the potential of Bacillus subtilis strain M4 at protecting plants against fungal diseases was demonstrated in different pathosystems. We provide evidence for the role of secreted ... [more ▼]

In this work, the potential of Bacillus subtilis strain M4 at protecting plants against fungal diseases was demonstrated in different pathosystems. We provide evidence for the role of secreted lipopeptides, and more particularly of fengycins, in the protective effect afforded by the strain against damping-off of bean seedlings caused by Pythium ultimum and against gray mold of apple in post-harvest disease. This role was demonstrated by the strong biocontrol activity of lipopeptide-enriched extracts and through the detection of inhibitory quantities of fengycins in infected tissues. Beside such a direct antagonism of the pathogen, we show that root pre-inoculation with M4 enabled the host plant to react more efficiently to subsequent pathogen infection on leaves. Fengycins could also be involved in this systemic resistance-eliciting effect of strain M4, as these molecules may induce the synthesis of plant phenolics involved in or derived from the defense-related phenylpropanoid metabolism. Much remains to be discovered about the mechanisms by which Bacillus spp suppress disease. Through this study on strain M4, we reinforce the interest in B. subtilis as a pathogen antagonist and plant defense-inducing agent. The secretion of cyclic fengycin-type lipopeptides may be tightly related to the expression of these two biocontrol traits. [less ▲]

Influence of moderate temperatures on myristoyl-CoA metabolism and acyl-CoA thioesterase activity in the psychrophilic antarctic yeast Rhodotorula aurantiaca.

in Journal of Biological Chemistry (2001), 276(16), 12691-6

The inability of psychrophilic microorganisms to grow at moderate temperatures (>20 degrees C) presently represents an unresolved thermodynamic paradox. Here we report for the psychrophilic yeast ... [more ▼]

The inability of psychrophilic microorganisms to grow at moderate temperatures (>20 degrees C) presently represents an unresolved thermodynamic paradox. Here we report for the psychrophilic yeast Rhodotorula aurantiaca A19, isolated from Antarctic ice, that the inability to grow at temperatures close to 20 degrees C is associated with profound alterations in cell morphology and integrity. High performance liquid chromatography analysis of the intracellular acyl-CoA esters revealed an abnormal accumulation of myristoyl-CoA (C14-CoA) in cells cultivated close to the nonpermissive temperature. Its concentration (500 microm) was found to be 28-fold higher than in cells cultivated at 0 degrees C. If one considers its ability to disrupt membrane bilayers and to inhibit many cellular enzymes and functions, intracellular myristoyl-CoA accumulation in the psychrophile R. aurantiaca represents one of the principal causes of growth arrest at moderate temperatures. Intracellular acyl-CoA concentrations are believed to be regulated by thioesterase activity. Thus in an attempt to explore the mechanism by which temperature disrupts myristoyl-CoA metabolism, we isolated and characterized a long chain acyl-CoA thioesterase. The monomeric 80-kDa thioesterase from the psychrophilic yeast shows a very strong specificity for myristoyl-CoA. The affinity for substrate and the catalytic efficiency of the thioesterase are optimal below 5 degrees C (temperatures habitually experienced by the strain) and dramatically decrease with increasing temperature. The loss of affinity for substrate is related to the intracellular increase of myristoyl-CoA concentration. Our observations reveal one of the probable mechanisms by which temperature fixes the limit of growth for this psychrophilic yeast. [less ▲]

Production process of a new bacteriocin. Effect of bioreactor scale up on biological activity against E. amylovora, phytopathogen agent of fruit tree fire blight.

Poster (1997, August)

The efficacy in vitro and in vivo of bacteriocin against Erwinia amylovora : comparison of biological and chemical control of fire blight

in Acta Horticulturae (1996), 411

A screening technique to isolate bacterial strains producing high molecular weight bacteriocins.

in Biotechnology Techniques (1994), 8(10), 751-754