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.
The consumers' demand for natural flavour and fragrances rises. To be natural, compounds have to result from the extraction of natural materials and/or to be transformed by natural means such as the use of enzymes or whole cells. Fungi are able to transform some fatty acids into lactones that can thus be natural. Although some parts of this subject have been reviewed several times, the present article proposes to review the different pathways utilised, the metabolic engineering strategies and some current concerns on the reactor application of the transformation including scaling up data. The main enzymatic steps are hydroxylation and β-oxidation in the traditional way, and lactone desaturation or Baeyer-Villiger oxidation. Although the pathway to produce γ-decalactone is rather well known, metabolic engineering strategies may result in significant improvements in the productivity. For the production of other lactones, a key step is the hydroxylation of fatty acids. Beside the biotransformation, increasing the production of the various lactones requires from biotechnologists to solve two main problems which are the toxicity of lactones toward the producing cell and the aeration of the emulsified reactor as the biochemical pathway is very sensitive to the level of available oxygen. The strategies employed to resolve these problems will be presented.
Aims: To analyse the influence of nitrogen and carbon sources on extracellular lipase production by Yarrowia lipolytica-overproducing mutant in order to optimize its production in large-scale bioreactors. Methods and Results: The level of lipase production and LIP2 induction, measured using an LIP2-LacZ reporter gene, were compared for different carbon and nitrogen sources and for different concentrations. The localization of the enzyme during growth was also determined by Western blotting analysis using a six-histidinetagged lipase. Significance and Impact of the Study: Tryptone N1 and oleic acid are the most suitable nitrogen and carbon sources for the production of the extracellular lipase by the Y. lipolytica mutant. Higher levels of lipase production were obtained as the tryptone concentration increased in the culture medium. Such a positive correlation was not observed with oleic acid media where the highest lipolytic productivities were obtained in the presence of low concentration. We also demonstrate that in the presence of oleic acid, lipase is cell-bound during the growth phase before being released in the media. Conclusions: This work provides a better understanding of the mechanism controlling LIP2 expression and, thus, extracellular lipase production in the yeast Y. lipolytica.
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